On Wed, Mar 30, 2022 at 10:52:54AM +0200, Maxime Ripard wrote:

On Tue, Mar 29, 2022 at 11:38:32PM +0530, Jagan Teki wrote:

...

Hi all,

I have implemented runtime display switching in the MIPI switch design where LVDS and HDMI bridges are selected with the help of runtime GPIO.

Initial discussion on the same can be found here, https://www.spinics.net/lists/dri-devel/msg318524.html

The implementation has been done by creating each connector at runtime. The default boot will create the LVDS connector and based on the HDMI plug-in the ISR.

1. forcing the LVDS to disconnect
2. call drm_kms_helper_hotplug_event
3. detach the bridge chain
4. attach the new bridge chain (HDMI)
5. call drm_kms_helper_hotplug_event

do the reverse when we unplug the HDMI cable.

So, the bridge chains are attached and detached based on GPIO Interrupt which is indeed identified based on the physical HDMIA connector.

Pipeline for LVDS, mxfsb => nwl-dsi => display-switch => sn65dsi83=> panel-bridge

Pipeline for HDMI, mxfsb => nwl-dsi => display-switch => adv7511 => display-connector

With this, implementation and I can able switch the displays with default DRM (without specific DRM applications) where the LVDS is ON by default and when HDMI plug-in the LVDS OFF/HDMI ON, and when HDMI unplug the HDMI OFF/LVDS ON.

However, with QT5 I can see the DRM Master ignoring hotplug event by returning 0 on drm_master_internal_acquire in drm_fb_helper_hotplug_event. With this the hotplug returned early so it cannot able to disconnect and connect the new switching connector.

Any help?

I'm not sure why you started another discussion with pretty much the same content, but you can't rely on userspace handling the hotplug event. You'll have to deal with the case where it just doesn't.

Well I missed the old thread, so I'm replying here.

You should not handle this at all from a hotplug.

The way kms works is roughly as follows:

1. hw output state changes 2. driver detects this (either through hpd interrupt or polling) 3. driver sends out hotplug uevent

That's it. Nothing else, no bridge rebinding, no link retaining is required.

Then either userspace or fbcon emulation reacts to this hotplug event by doing an atomic modeset, where it hopefully disables the old output and re-enables the new output. Your atomic_check needs to validate that everything is all right (i.e. not enabling both at the same time).

Note that if you change stuff underneath, then that tends to seriously upset atomic users. Also you should try to continue supporting at least page flips with the wrong config, compositors otherwise tend to crash.

This also means that if userspace doesn't handle hotplug events, then you might end up with a black screen. That's ok. We try to avoid that when it's practical (e.g. dp sst link retraining), but not when it's too hard (dp mst hot-replug relies on userspace restoring everything).

Finally exchanging the bridge chain isn't supported, there's no locking for that since it's assumed to be invariant over the lifetim of the drm_device instance. The simplest way to make that happen right now is to have 2 drm_encoder instances, one with the lvds bridge chain, the other with the hdmi bridge chain, and select the right encoder/bridge chain depending upon which output userspace picks.

Also ofc your atomic_check needs to make sure that they're not both enabled at the same time :-)

I wouldn't try to make bridge chains exchangeable instead, that's headaches - e.g. with dp mst we've also opted for a bunch of fake drm_encoders to model that kind of switching. -Daniel

On Thu, Mar 31, 2022 at 12:14:31AM +0530, Jagan Teki wrote:

On Wed, Mar 30, 2022 at 3:27 PM Daniel Vetter daniel@ffwll.ch wrote:

...

On Wed, Mar 30, 2022 at 10:52:54AM +0200, Maxime Ripard wrote:

...

On Tue, Mar 29, 2022 at 11:38:32PM +0530, Jagan Teki wrote:

...

Hi all,

I have implemented runtime display switching in the MIPI switch design where LVDS and HDMI bridges are selected with the help of runtime GPIO.

Initial discussion on the same can be found here, https://www.spinics.net/lists/dri-devel/msg318524.html

The implementation has been done by creating each connector at runtime. The default boot will create the LVDS connector and based on the HDMI plug-in the ISR.

1. forcing the LVDS to disconnect
2. call drm_kms_helper_hotplug_event
3. detach the bridge chain
4. attach the new bridge chain (HDMI)
5. call drm_kms_helper_hotplug_event

do the reverse when we unplug the HDMI cable.

So, the bridge chains are attached and detached based on GPIO Interrupt which is indeed identified based on the physical HDMIA connector.

Pipeline for LVDS, mxfsb => nwl-dsi => display-switch => sn65dsi83=> panel-bridge

Pipeline for HDMI, mxfsb => nwl-dsi => display-switch => adv7511 => display-connector

With this, implementation and I can able switch the displays with default DRM (without specific DRM applications) where the LVDS is ON by default and when HDMI plug-in the LVDS OFF/HDMI ON, and when HDMI unplug the HDMI OFF/LVDS ON.

However, with QT5 I can see the DRM Master ignoring hotplug event by returning 0 on drm_master_internal_acquire in drm_fb_helper_hotplug_event. With this the hotplug returned early so it cannot able to disconnect and connect the new switching connector.

Any help?

I'm not sure why you started another discussion with pretty much the same content, but you can't rely on userspace handling the hotplug event. You'll have to deal with the case where it just doesn't.

Well I missed the old thread, so I'm replying here.

You should not handle this at all from a hotplug.

Just to be clear. ISR is handling bridge detach and attach management and call hotplug not the hotplug don't know anything about bridges here.

...

The way kms works is roughly as follows:

1. hw output state changes
2. driver detects this (either through hpd interrupt or polling)
3. driver sends out hotplug uevent

That's it. Nothing else, no bridge rebinding, no link retaining is required.

Then either userspace or fbcon emulation reacts to this hotplug event by doing an atomic modeset, where it hopefully disables the old output and re-enables the new output. Your atomic_check needs to validate that everything is all right (i.e. not enabling both at the same time).

Does it mean the userspace knows when to disconnect and connect the LVDS or HDMI? What if display-switch ISR will disconnect LVDS and connect HDMI when HPD is On and connect LVDS and disconnect HDMI when HDP is Off of-course it makes only one enable at a time.

...

Note that if you change stuff underneath, then that tends to seriously upset atomic users. Also you should try to continue supporting at least page flips with the wrong config, compositors otherwise tend to crash.

This also means that if userspace doesn't handle hotplug events, then you might end up with a black screen. That's ok. We try to avoid that when it's practical (e.g. dp sst link retraining), but not when it's too hard (dp mst hot-replug relies on userspace restoring everything).

This is what I'm not sure about it as normal FB testing without any specific applications like QT - I can still see the switching works well without any issues. However, QT applications seem to control the hotplug by acquiring DRM master. is there any way from kernel side to ignore those application control over hotplug so that I can switch even the QT application as normal FB does? just to understand my testing and flow?

No, that's not how kms works.

When fbcon is active, then fbcon takes over all responsibilities of a drm master. Including reacting to hotplug events.

If your QT app directly uses kms, but doesn't handle hotplugs, then yes nothing at all happens. But that's just a userspace bug, not a kernel bug, and we really should _not_ work around random userspace issues like this in the kernel.

Actually we cannot, because doing so would upset real kms compositors, since the kernel doing funny stuff underneath it will at best confuse it. And it some cases it resulted in crashes.

...

Finally exchanging the bridge chain isn't supported, there's no locking for that since it's assumed to be invariant over the lifetim of the drm_device instance. The simplest way to make that happen right now is to have 2 drm_encoder instances, one with the lvds bridge chain, the other with the hdmi bridge chain, and select the right encoder/bridge chain depending upon which output userspace picks.

Does it mean to initialize to encoder instances and start attaching those to respective bridge pipelines?

I haven't checked, but I think it's not possible to change the bridge chaining after drm_dev_register is called due to locking.

So doing bridge attach/detach from the hotplug handler is a no-go. The bridges need to be set up at driver load.

Also with this design each bridge chain has its own drm_connector (HDMI and LVDS, if I got you right). But that's just how bridges work.

...

Also ofc your atomic_check needs to make sure that they're not both enabled at the same time :-)

I wouldn't try to make bridge chains exchangeable instead, that's headaches - e.g. with dp mst we've also opted for a bunch of fake drm_encoders to model that kind of switching.

Can you link some references in the source tree for it to make a quick check?

See the atomic_best_encoder callback, doc link here:

https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html?highlight=atom...

Although thinking about this you should have only 1 encoder for each drm_connector (if you go with separate connector for hdmi and lvds), and in that case the atomic helpers will take care of everything for you. Well except making sure that only one encoder of the two is enabled at the same time. -Daniel

Thanks, Jagan.

Hi Daniel,

On Wed, Mar 30, 2022 at 3:27 PM Daniel Vetter daniel@ffwll.ch wrote:

On Wed, Mar 30, 2022 at 10:52:54AM +0200, Maxime Ripard wrote:

...

On Tue, Mar 29, 2022 at 11:38:32PM +0530, Jagan Teki wrote:

...

Hi all,

I have implemented runtime display switching in the MIPI switch design where LVDS and HDMI bridges are selected with the help of runtime GPIO.

Initial discussion on the same can be found here, https://www.spinics.net/lists/dri-devel/msg318524.html

The implementation has been done by creating each connector at runtime. The default boot will create the LVDS connector and based on the HDMI plug-in the ISR.

1. forcing the LVDS to disconnect
2. call drm_kms_helper_hotplug_event
3. detach the bridge chain
4. attach the new bridge chain (HDMI)
5. call drm_kms_helper_hotplug_event

do the reverse when we unplug the HDMI cable.

So, the bridge chains are attached and detached based on GPIO Interrupt which is indeed identified based on the physical HDMIA connector.

Pipeline for LVDS, mxfsb => nwl-dsi => display-switch => sn65dsi83=> panel-bridge

Pipeline for HDMI, mxfsb => nwl-dsi => display-switch => adv7511 => display-connector

With this, implementation and I can able switch the displays with default DRM (without specific DRM applications) where the LVDS is ON by default and when HDMI plug-in the LVDS OFF/HDMI ON, and when HDMI unplug the HDMI OFF/LVDS ON.

However, with QT5 I can see the DRM Master ignoring hotplug event by returning 0 on drm_master_internal_acquire in drm_fb_helper_hotplug_event. With this the hotplug returned early so it cannot able to disconnect and connect the new switching connector.

Any help?

I'm not sure why you started another discussion with pretty much the same content, but you can't rely on userspace handling the hotplug event. You'll have to deal with the case where it just doesn't.

Well I missed the old thread, so I'm replying here.

You should not handle this at all from a hotplug.

The way kms works is roughly as follows:

1. hw output state changes
2. driver detects this (either through hpd interrupt or polling)
3. driver sends out hotplug uevent

That's it. Nothing else, no bridge rebinding, no link retaining is required.

Then either userspace or fbcon emulation reacts to this hotplug event by doing an atomic modeset, where it hopefully disables the old output and re-enables the new output. Your atomic_check needs to validate that everything is all right (i.e. not enabling both at the same time).

Note that if you change stuff underneath, then that tends to seriously upset atomic users. Also you should try to continue supporting at least page flips with the wrong config, compositors otherwise tend to crash.

This also means that if userspace doesn't handle hotplug events, then you might end up with a black screen. That's ok. We try to avoid that when it's practical (e.g. dp sst link retraining), but not when it's too hard (dp mst hot-replug relies on userspace restoring everything).

Finally exchanging the bridge chain isn't supported, there's no locking for that since it's assumed to be invariant over the lifetim of the drm_device instance. The simplest way to make that happen right now is to have 2 drm_encoder instances, one with the lvds bridge chain, the other with the hdmi bridge chain, and select the right encoder/bridge chain depending upon which output userspace picks.

I've created 2 instances of encoders. endpoint 0 for HDMI bridge chain and endpoint 1 for LVDS bridge chain. Each bridge chain uses a respective encoder instance in order to start attaching the bridge like below.

1. find the bridge at endpoint 0 2. drm_bridge_attach(&mxsfb->encoder[0], mxsfb->bridge[0], NULL, 0)

and repeat for endpoint 1

The bridge chain established fine for endpoint 0 but returned -EBUSY while the bridge chain attached for endpoint 1. looks like bridge->dev is still being used in endpoint 0 even though we have a separate bridge point from mxsfb.

Any thought on how to establish the dual bridge chain here?

Thanks, Jagan.

On Tue, Jun 7, 2022 at 8:04 PM Daniel Vetter daniel@ffwll.ch wrote:

On Thu, 2 Jun 2022 at 17:43, Jagan Teki jagan@amarulasolutions.com wrote:

...

Hi Daniel,

On Wed, Mar 30, 2022 at 3:27 PM Daniel Vetter daniel@ffwll.ch wrote:

...

On Wed, Mar 30, 2022 at 10:52:54AM +0200, Maxime Ripard wrote:

...

On Tue, Mar 29, 2022 at 11:38:32PM +0530, Jagan Teki wrote:

...

Hi all,

I have implemented runtime display switching in the MIPI switch design where LVDS and HDMI bridges are selected with the help of runtime GPIO.

Initial discussion on the same can be found here, https://www.spinics.net/lists/dri-devel/msg318524.html

The implementation has been done by creating each connector at runtime. The default boot will create the LVDS connector and based on the HDMI plug-in the ISR.

1. forcing the LVDS to disconnect
2. call drm_kms_helper_hotplug_event
3. detach the bridge chain
4. attach the new bridge chain (HDMI)
5. call drm_kms_helper_hotplug_event

do the reverse when we unplug the HDMI cable.

So, the bridge chains are attached and detached based on GPIO Interrupt which is indeed identified based on the physical HDMIA connector.

Pipeline for LVDS, mxfsb => nwl-dsi => display-switch => sn65dsi83=> panel-bridge

Pipeline for HDMI, mxfsb => nwl-dsi => display-switch => adv7511 => display-connector

With this, implementation and I can able switch the displays with default DRM (without specific DRM applications) where the LVDS is ON by default and when HDMI plug-in the LVDS OFF/HDMI ON, and when HDMI unplug the HDMI OFF/LVDS ON.

However, with QT5 I can see the DRM Master ignoring hotplug event by returning 0 on drm_master_internal_acquire in drm_fb_helper_hotplug_event. With this the hotplug returned early so it cannot able to disconnect and connect the new switching connector.

Any help?

I'm not sure why you started another discussion with pretty much the same content, but you can't rely on userspace handling the hotplug event. You'll have to deal with the case where it just doesn't.

Well I missed the old thread, so I'm replying here.

You should not handle this at all from a hotplug.

The way kms works is roughly as follows:

1. hw output state changes
2. driver detects this (either through hpd interrupt or polling)
3. driver sends out hotplug uevent

That's it. Nothing else, no bridge rebinding, no link retaining is required.

Then either userspace or fbcon emulation reacts to this hotplug event by doing an atomic modeset, where it hopefully disables the old output and re-enables the new output. Your atomic_check needs to validate that everything is all right (i.e. not enabling both at the same time).

Note that if you change stuff underneath, then that tends to seriously upset atomic users. Also you should try to continue supporting at least page flips with the wrong config, compositors otherwise tend to crash.

This also means that if userspace doesn't handle hotplug events, then you might end up with a black screen. That's ok. We try to avoid that when it's practical (e.g. dp sst link retraining), but not when it's too hard (dp mst hot-replug relies on userspace restoring everything).

Finally exchanging the bridge chain isn't supported, there's no locking for that since it's assumed to be invariant over the lifetim of the drm_device instance. The simplest way to make that happen right now is to have 2 drm_encoder instances, one with the lvds bridge chain, the other with the hdmi bridge chain, and select the right encoder/bridge chain depending upon which output userspace picks.

I've created 2 instances of encoders. endpoint 0 for HDMI bridge chain and endpoint 1 for LVDS bridge chain. Each bridge chain uses a respective encoder instance in order to start attaching the bridge like below.

1. find the bridge at endpoint 0
2. drm_bridge_attach(&mxsfb->encoder[0], mxsfb->bridge[0], NULL, 0)

and repeat for endpoint 1

The bridge chain established fine for endpoint 0 but returned -EBUSY while the bridge chain attached for endpoint 1. looks like bridge->dev is still being used in endpoint 0 even though we have a separate bridge point from mxsfb.

Any thought on how to establish the dual bridge chain here?

Are you using 2 different struct drm_bridge for this? Reusing the same drm_bridge for the 2nd encoder and endpoint is the only thing I can come up with that would result in this.

Yes, I did try to re-use the same bridge pointer. drm_bridge_attach giving an -EBUSY while attaching the 2nd bridge chain.

Jagan.

On Wed, Jun 08, 2022 at 05:41:29PM +0200, Daniel Vetter wrote:

On Tue, Jun 07, 2022 at 11:03:09PM +0530, Jagan Teki wrote:

...

On Tue, Jun 7, 2022 at 8:04 PM Daniel Vetter daniel@ffwll.ch wrote:

...

On Thu, 2 Jun 2022 at 17:43, Jagan Teki jagan@amarulasolutions.com wrote:

...

Hi Daniel,

On Wed, Mar 30, 2022 at 3:27 PM Daniel Vetter daniel@ffwll.ch wrote:

...

On Wed, Mar 30, 2022 at 10:52:54AM +0200, Maxime Ripard wrote:

...

On Tue, Mar 29, 2022 at 11:38:32PM +0530, Jagan Teki wrote: > Hi all, > > I have implemented runtime display switching in the MIPI switch design > where LVDS and HDMI bridges are selected with the help of runtime > GPIO. > > Initial discussion on the same can be found here, > https://www.spinics.net/lists/dri-devel/msg318524.html > > The implementation has been done by creating each connector at > runtime. The default boot will create the LVDS connector and based on > the HDMI plug-in the ISR. > > 1. forcing the LVDS to disconnect > 2. call drm_kms_helper_hotplug_event > 3. detach the bridge chain > 4. attach the new bridge chain (HDMI) > 5. call drm_kms_helper_hotplug_event > > do the reverse when we unplug the HDMI cable. > > So, the bridge chains are attached and detached based on GPIO > Interrupt which is indeed identified based on the physical HDMIA > connector. > > Pipeline for LVDS, > mxfsb => nwl-dsi => display-switch => sn65dsi83=> panel-bridge > > Pipeline for HDMI, > mxfsb => nwl-dsi => display-switch => adv7511 => display-connector > > With this, implementation and I can able switch the displays with > default DRM (without specific DRM applications) where the LVDS is ON > by default and when HDMI plug-in the LVDS OFF/HDMI ON, and when HDMI > unplug the HDMI OFF/LVDS ON. > > However, with QT5 I can see the DRM Master ignoring hotplug event by > returning 0 on drm_master_internal_acquire in > drm_fb_helper_hotplug_event. With this the hotplug returned early so > it cannot able to disconnect and connect the new switching connector. > > Any help?

I'm not sure why you started another discussion with pretty much the same content, but you can't rely on userspace handling the hotplug event. You'll have to deal with the case where it just doesn't.

Well I missed the old thread, so I'm replying here.

You should not handle this at all from a hotplug.

The way kms works is roughly as follows:

1. hw output state changes
2. driver detects this (either through hpd interrupt or polling)
3. driver sends out hotplug uevent

That's it. Nothing else, no bridge rebinding, no link retaining is required.

Then either userspace or fbcon emulation reacts to this hotplug event by doing an atomic modeset, where it hopefully disables the old output and re-enables the new output. Your atomic_check needs to validate that everything is all right (i.e. not enabling both at the same time).

Note that if you change stuff underneath, then that tends to seriously upset atomic users. Also you should try to continue supporting at least page flips with the wrong config, compositors otherwise tend to crash.

This also means that if userspace doesn't handle hotplug events, then you might end up with a black screen. That's ok. We try to avoid that when it's practical (e.g. dp sst link retraining), but not when it's too hard (dp mst hot-replug relies on userspace restoring everything).

Finally exchanging the bridge chain isn't supported, there's no locking for that since it's assumed to be invariant over the lifetim of the drm_device instance. The simplest way to make that happen right now is to have 2 drm_encoder instances, one with the lvds bridge chain, the other with the hdmi bridge chain, and select the right encoder/bridge chain depending upon which output userspace picks.

I've created 2 instances of encoders. endpoint 0 for HDMI bridge chain and endpoint 1 for LVDS bridge chain. Each bridge chain uses a respective encoder instance in order to start attaching the bridge like below.

1. find the bridge at endpoint 0
2. drm_bridge_attach(&mxsfb->encoder[0], mxsfb->bridge[0], NULL, 0)

and repeat for endpoint 1

The bridge chain established fine for endpoint 0 but returned -EBUSY while the bridge chain attached for endpoint 1. looks like bridge->dev is still being used in endpoint 0 even though we have a separate bridge point from mxsfb.

Any thought on how to establish the dual bridge chain here?

Are you using 2 different struct drm_bridge for this? Reusing the same drm_bridge for the 2nd encoder and endpoint is the only thing I can come up with that would result in this.

Yes, I did try to re-use the same bridge pointer. drm_bridge_attach giving an -EBUSY while attaching the 2nd bridge chain.

Yeah that doesn't work. You can embed 2 drm_bridge within the same struct, that should work. So essentially 1 platform_driver which registers 2 bridges. But binding the same bridge twice is an error, because a bridge is strictly a 1:1 connection. Not a 2:2 connection.

Two clarify: That struct with the 2 drm_bridge would be the platform driver private you register, not part of your platform_driver structure ofc. It needs to be attached to the struct platform_dev, not the driver. Just in case I confused you here even more :-) -Daniel