Renesas rcar-du and DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE

[Adam Ford]

On Wed, Dec 29, 2021 at 10:19 PM Charles Stevens <chazste at yahoo.com> wrote:
>
> 
> Hi All,
>      I am working on a platform based on the Renesas RZ/G2 SoC family. This chip uses the rcar-du driver for the display. I would like to submit a patch to address the fact that the driver does not check/honor the flag DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE. My issue is that I would like to make as small a change to the driver as possible, but the panel bus_flags don't seem to even make it to the crtc driver. The crtc driver seems to use adjusted_mode to set the HSYNC and VSYNC polarity and as I said ignores the pixel clock polarity leaving it at the default of driving on the falling edge. In my investigations so far I have not figured out how to chase the pointers from the CRTC to the bridge to the panel in order to be able to look at bus_flags. My current approach also modifies the encoder initialization to cache the needed panel and then find the attached encoder during CRTC initialization to find the bus flags. This seems like a lot of work and not something that would be accepted as a patch. The OMAP DSS seems to have problems accessing this flag as well. The TI driver goes so far as to document the current approach as a HACK and suggest a fairly large change to the driver to address the problem. Am I missing something? Is there an easy way to get from a drm_crtc to a drm_panel that is in the same pipeline?
>
>     Any pointers would be greatly appreciated!
+  Laurent, Kieran

Charles,

I added Laurent and Kieran because they appear as the maintainers for
the rcar-du driver.

adam

>
> Thanks!
>
> -charles