Hi Laurent, > Am 23.09.2021 um 11:27 schrieb Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>: > > Hi Nikolaus, > > 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. Hence it checks for ! DRM_BRIDGE_ATTACH_NO_CONNECTOR which seems to be the right thing to do on current platforms that use it. For CI20/jz4780 we just add a specialisation of the generic dw-hdmi to make HDMI work. Now this patch for drm/ingenic wants the opposite definition and create its own connector. This fails even if we remove the check (then we have two interfering connectors). > We're moving > towards requiring DRM_BRIDGE_ATTACH_NO_CONNECTOR for all new code, so it > will have to be done eventually. So from my view drm/ingenic wants to already enforce this rule and breaks dw-hdmi. IMHO it should either handle this situation gracefully or include a fix for dw-hdmi.c to keep it compatible. BR and thanks, Nikolaus
