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. > 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. -- Regards, Laurent Pinchart
