Hi Laurent,
Am 23.09.2021 um 12:03 schrieb Laurent Pinchart laurent.pinchart@ideasonboard.com:
Hi Nikolaus,
On Thu, Sep 23, 2021 at 11:55:56AM +0200, H. Nikolaus Schaller wrote:
Am 23.09.2021 um 11:27 schrieb Laurent Pinchart: On Thu, Sep 23, 2021 at 11:19:23AM +0200, H. Nikolaus Schaller wrote:
> + ret = drm_bridge_attach(encoder, &ib->bridge, NULL, > + DRM_BRIDGE_ATTACH_NO_CONNECTOR);
DRM_BRIDGE_ATTACH_NO_CONNECTOR makes it fundamentally incompatible with synopsys/dw_hdmi.c That driver checks for DRM_BRIDGE_ATTACH_NO_CONNECTOR being NOT present, since it wants to register its own connector through dw_hdmi_connector_create(). It does it for a reason: the dw-hdmi is a multi-function driver which does HDMI and DDC/EDID stuff in a single driver (because I/O registers and power management seem to be shared).
The IT66121 driver does all of that too, and does not need DRM_BRIDGE_ATTACH_NO_CONNECTOR. The drm_bridge_funcs struct has callbacks to handle cable detection and DDC stuff.
Since I do not see who could split this into a separate bridge and a connector driver and test it on multiple SoC platforms (there are at least 3 or 4), I think modifying the fundamentals of the dw-hdmi architecture just to get CI20 HDMI working is not our turf.
You could have a field in the dw-hdmi pdata structure, that would instruct the driver whether or not it should use the new API. Ugly, I know, and would probably duplicate a lot of code, but that would allow other drivers to be updated at a later date.
Yes, would be very ugly.
But generally who has the knowledge (and time) to do this work? And has a working platform to test (jz4780 isn't a good development environment)?
The driver seems to have a turbulent history starting 2013 in staging/imx and apparently it was generalized since then... Is Laurent currently dw-hdmi maintainer?
"Maintainer" would be an overstatement. I've worked on that driver in the past, and I still use it, but don't have time to really maintain it. I've also been told that Synopsys required all patches for that driver developed using documentation under NDA to be submitted internally to them first before being published, so I decided to stop contributing instead of agreeing with this insane process. There's public documentation about the IP in some NXP reference manuals though, so it should be possible to still move forward without abiding by this rule.
Therefore the code here should be able to detect if drm_bridge_attach() already creates and attaches a connector and then skip the code below.
Not that easy, unfortunately. On one side we have dw-hdmi which checks that DRM_BRIDGE_ATTACH_NO_CONNECTOR is not set, and on the other side we have other drivers like the IT66121 which will fail if this flag is not set.
Ok, I see. You have to handle contradicting cases here.
Would it be possible to run it with DRM_BRIDGE_ATTACH_NO_CONNECTOR first and retry if it fails without?
But IMHO the return value (in error case) is not well defined. So there must be a test if a connector has been created (I do not know how this would work).
Another suggestion: can you check if there is a downstream connector defined in device tree (dw-hdmi does not need such a definition)? If not we call it with 0 and if there is one we call it with DRM_BRIDGE_ATTACH_NO_CONNECTOR and create one?
I haven't followed the ful conversation, what the reason why DRM_BRIDGE_ATTACH_NO_CONNECTOR can't always be use here ?
The synopsys driver creates its own connector through dw_hdmi_connector_create() because the IP handles DDC/EDID directly.
That doesn't require creating a connector though. The driver implements drm_bridge_funcs.get_edid(), which is used to get the EDID without the need to create a connector in the dw-hdmi driver.
Ah, ok.
But then we still have issues.
Firstly I would assume that get_edid only works properly if it is initialized through dw_hdmi_connector_create().
Next, in the current code, passing DRM_BRIDGE_ATTACH_NO_CONNECTOR to dw_hdmi_bridge_attach() indeed does not call dw_hdmi_connector_create() but returns 0.
This patch 6/6 makes drm/ingenic unconditionally require a connector to be attached which is defined somewhere else (device tree e.g. "connector-hdmi") unrelated to dw-hdmi. Current upstream code for drm/ingenic does not init/attach such a connector on its own so it did work before.
I.e. I think we can't just use parts of dw-hdmi.
If drm_bridge_attach() would return some errno if DRM_BRIDGE_ATTACH_NO_CONNECTOR is set, initialization in ingenic_drm_bind() would fail likewise with "Unable to attach bridge".
So in any case dw-hdmi is broken by this drm/ingenic patch unless someone reworks it to make it compatible.
Another issue is that dw_hdmi_connector_create() does not only do dcd/edid but appears to detects hot plug and does some special initialization. So we probably loose hotplug detect if we just use drm_bridge_funcs.get_edid().
I come to the conclusion that not creating a specific connector in dw-hdmi and relying on a generic connector does not seem to be an option with current code proposals.
In such a situation the question is what the least invasive surgery is to avoid complications and lenghty regression tests on unknown platforms. IMHO it is leaving (mature) dw-hdmi untouched and make attachment of a connector in ingenic_drm_bind() depend on some condition.
BR and thanks, Nikolaus