Hi,
On Fri, 2019-05-10 at 16:54 +0200, Daniel Vetter wrote:
On Fri, May 10, 2019 at 2:12 PM Paul Kocialkowski paul.kocialkowski@bootlin.com wrote:
Hi,
On Tue, 2019-05-07 at 21:57 +0530, Ramalingam C wrote:
DRM API for generating uevent for a status changes of connector's property.
This uevent will have following details related to the status change:
HOTPLUG=1, CONNECTOR=<connector_id> and PROPERTY=<property_id>
Need ACK from this uevent from userspace consumer.
So we just had some discussions over on IRC and at about the hotplug issue and came up with similar ideas: https://lists.freedesktop.org/archives/dri-devel/2019-May/217408.html
The conclusions of these discussions so far would be to have a more or less fine grain of uevent reporting depending on what happened. The point is that we need to cover different cases:
- one or more properties changed;
- the connector status changed;
- something else about the connector changed (e.g. EDID/modes)
For the first case, we can send out: HOTPLUG=1 CONNECTOR=<id> PROPERTY=<id>
and no reprobe is required.
For the second one, something like: HOTPLUG=1 CONNECTOR=<id> STATUS=Connected/Disconnected
and a connector probe is needed for connected, but not for disconnected;
For the third one, we can only indicate the connector: HOTPLUG=1 CONNECTOR=<id>
and a reprobe of the connector is always needed
There's no material difference between this one and the previous one. Plus there's no beenfit in supplying the actual value of the property, i.e. we can reuse the same PROPERTY=<id-of-status-property> trick.
That's the idea, but we need to handle status changes differently than properties, since as far as I know, connected/unconnected status is not exposed as a prop for the connector.
Here's why:
- A side effect of forcing a probe on a connector is that you get to
read all the properties, so supplying them is kinda pointless.
Agreed, except for the status case where it's useful to know it's a disconnect, because we don't need any probe step in that case.
- You can read STATUS without forcing a reprobe, if you want to avoid
the reprobe for disconnected. I'd kinda not recommend that though, feels a bit like overoptimizing. And for reasonable connectors (i.e. dp) reprobing a disconnected output is fast. HDMI is ... less reasonable unfortunately, but oh well.
How would that be retreived then? From the looks of it, that's a MODE_GETCONNECTOR ioctl and I was under the impression this is what does the full reprobe.
Not sure what issues could arise in case of disconnect without reprobe -- at least I don't see why userspace should have to do anything in particular except no longer using the connector, even in complex DP MST cases.
- There's no way to only reprobe status, you can only ever reprobe
everything with the current ioctl and implementations. Having an option to reprobe only parts of it doesn't seem useful to me (we need to read the EDID anyway, and that's the expensive part of reprobing in almost all cases).
Agreed.
In a way PROPERTY=<status-prop-id> simply tells userspace that it needs to reprobe this connector.
I thought we could access the props alone, which avoids doing a reprobe when the kernel knows that only a prop or a set of props changed and do not require a full reprobe. That's the first case I was mentionning.
At that point we need to figure out whether this is a good uapi or not, and that's where the epoch comes in. There's two reasons for an epoch:
- We need it internally because I'm not goinig to wire a new return
value through hundreds of connector probe functions. It's much easier to have an epoch counter which we set from e.g. drm_set_edid and similar functions that update probe state.
I don't think I'm following what issue this is trying to solve internally.
- If userspace misses an event and there's no epoch, we're forcing
userspace to reprobe everything. Use case would be if a compositor is switched away we probably don't want to piss of the current compositor by blocking it's own probe kernel calls by doing our own (probe is single-threaded in the kernel through the dev->mode_config.mutex). If it can read the epoch property (which it can do without forcing a reprobe) userspace would know which connectors it needs to check and reprobe.
Hence why epoch, it's a bit more robust userspace api. Ofc you could also require that userspace needs to keep parsing all uevents and make a list of all connectors it needs to reprobe when it's back to being the active compositor. But just comparing a current epoch with the one you cached from the last full probe is much easier.
Fair enough, I think it's a fine idea for robustness yes, but I think we could also provide extra info in the uevent when relevant and not rely on that entirely.
Another thing: None of this we can for connectors with unreliable hdp. Or at least you'll piss of users if you cache always. The sad thing is that HDMI is unreliable, at least on some machines/screen combos (you never get a hpd irq if you plug in/unplug). So real compositors still need to reprobe when the user asks for it. igt can probably get away without reprobing.
I wonder how that is handled currently and how a user action can solve the issue without any notification from the kernel. Maybe a need a better understanding of that case to have a clearer idea.
Cheers,
Paul
-Daniel
Then we still have the legacy case: HOTPLUG=1
where userspace is expected to reprobe all the connectors.
I think this would deserve to be a separate series on its own. So I am proposing to take this one off your plate and come up with another seres implementing this proposal. What do you think?
Cheers,
Paul
v2: Minor fixes at KDoc comments [Daniel] v3: Check the property is really attached with connector [Daniel]
Signed-off-by: Ramalingam C ramalingam.c@intel.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
drivers/gpu/drm/drm_sysfs.c | 35 +++++++++++++++++++++++++++++++++++ include/drm/drm_sysfs.h | 5 ++++- 2 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c index 18b1ac442997..63fa951a20db 100644 --- a/drivers/gpu/drm/drm_sysfs.c +++ b/drivers/gpu/drm/drm_sysfs.c @@ -21,6 +21,7 @@ #include <drm/drm_sysfs.h> #include <drm/drmP.h> #include "drm_internal.h" +#include "drm_crtc_internal.h"
#define to_drm_minor(d) dev_get_drvdata(d) #define to_drm_connector(d) dev_get_drvdata(d) @@ -320,6 +321,9 @@ void drm_sysfs_lease_event(struct drm_device *dev)
- Send a uevent for the DRM device specified by @dev. Currently we only
- set HOTPLUG=1 in the uevent environment, but this could be expanded to
- deal with other types of events.
- Any new uapi should be using the drm_sysfs_connector_status_event()
*/
- for uevents on connector status change.
void drm_sysfs_hotplug_event(struct drm_device *dev) { @@ -332,6 +336,37 @@ void drm_sysfs_hotplug_event(struct drm_device *dev) } EXPORT_SYMBOL(drm_sysfs_hotplug_event);
+/**
- drm_sysfs_connector_status_event - generate a DRM uevent for connector
- property status change
- @connector: connector on which property status changed
- @property: connector property whoes status changed.
- Send a uevent for the DRM device specified by @dev. Currently we
- set HOTPLUG=1 and connector id along with the attached property id
- related to the status change.
- */
+void drm_sysfs_connector_status_event(struct drm_connector *connector,
struct drm_property *property)+{
struct drm_device *dev = connector->dev;char hotplug_str[] = "HOTPLUG=1", conn_id[30], prop_id[30];char *envp[4] = { hotplug_str, conn_id, prop_id, NULL };WARN_ON(!drm_mode_obj_find_prop_id(&connector->base,property->base.id));snprintf(conn_id, ARRAY_SIZE(conn_id),"CONNECTOR=%u", connector->base.id);snprintf(prop_id, ARRAY_SIZE(prop_id),"PROPERTY=%u", property->base.id);DRM_DEBUG("generating connector status event\n");kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE, envp);+} +EXPORT_SYMBOL(drm_sysfs_connector_status_event);
static void drm_sysfs_release(struct device *dev) { kfree(dev); diff --git a/include/drm/drm_sysfs.h b/include/drm/drm_sysfs.h index 4f311e836cdc..d454ef617b2c 100644 --- a/include/drm/drm_sysfs.h +++ b/include/drm/drm_sysfs.h @@ -4,10 +4,13 @@
struct drm_device; struct device; +struct drm_connector; +struct drm_property;
int drm_class_device_register(struct device *dev); void drm_class_device_unregister(struct device *dev);
void drm_sysfs_hotplug_event(struct drm_device *dev);
+void drm_sysfs_connector_status_event(struct drm_connector *connector,
struct drm_property *property);#endif
-- Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com