[linux-sunxi] Re: [PATCH v7 4/8] drm/sunxi: Add DT bindings documentation of Allwinner HDMI

[Icenowy Zheng]

30.11.2016, 18:44, "Jean-Francois Moine" <moinejf at free.fr>:
> On Wed, 30 Nov 2016 11:52:25 +0200
> Laurent Pinchart <laurent.pinchart at ideasonboard.com> wrote:
>
>>  Hi Jean-François,
>>
>>  On Wednesday 30 Nov 2016 10:27:57 Jean-Francois Moine wrote:
>>  > On Wed, 30 Nov 2016 10:20:21 +0200 Laurent Pinchart wrote:
>>  > >> Well, I don't see what this connector can be.
>>  > >> May you give me a DT example?
>>  > >
>>  > > Sure.
>>  > >
>>  > > arch/arm/boot/dts/r8a7791-koelsch.dts
>>  > >
>>  > > /* HDMI encoder */
>
>         [snip]
>>  > > /* HDMI connector */
>>  > >
>>  > > hdmi-out {
>>  > > compatible = "hdmi-connector";
>>  > > type = "a";
>>  > >
>>  > > port {
>>  > > hdmi_con: endpoint {
>>  > > remote-endpoint = <&adv7511_out>;
>>  > > };
>>  > > };
>>  > > };
>
>         [snip]
>>  > - what does the software do with the connector type?
>>
>>  That's up to the software to decide, the DT bindings should describe the
>>  hardware in the most accurate and usable way for the OS as possible. One of my
>>  longer term goals is to add connector drivers to handle DDC and HPD when
>>  they're not handled by the encoder (they are in the above example).
>>
>>  If the DDC was connected to a general-purpose I2C bus of the SoC, and the HPD
>>  to a GPIO, we would have
>>
>>          hdmi-out {
>>                  compatible = "hdmi-connector";
>>                  type = "a";
>>                  /* I2C bus and GPIO references are made up for the example */
>>                  ddc-i2c-bus = <&i2c4>;
>>                  hpd-gpios = <&gpio4 7 GPIO_ACTIVE_HIGH>
>>
>>                  port {
>>                          hdmi_con: endpoint {
>>                                  remote-endpoint = <&adv7511_out>;
>>                          };
>>                  };
>>          };
>>
>>  and both HPD and EDID reading should be handled by the connector driver.
>
>         [snip]
>
> Hi Laurent,
>
> OK. I understand. This connector complexity should be added in all DTs,
> and the same code would be used.
>
> Actually, for component binding, I use drm_of_component_probe():
>
> - from the DRM master, loop on the "ports" phandle array and bind the
>   CRTCs,
>
> - for each CRTC, loop on the first remote port level and bind the
>   encoders/connectors
>
> Now, this should be:
>
> - from the DRM master, loop on the first remote ports level and bind
>   the CRTCs,
>
> - for each CRTC, loop on the second remote port level and bind the
>   encoders (and bridges?),
>
> - for each encoder, loop on the third remote port level and bind the
>   connectors.
>
> Then, it would be nice to have a generic function for doing this job.
>
> Otherwise, from your description:
>
>>          hdmi-out {
>>                  compatible = "hdmi-connector";
>>                  type = "a";
>>                  /* I2C bus and GPIO references are made up for the example */
>>                  ddc-i2c-bus = <&i2c4>;
>>                  hpd-gpios = <&gpio4 7 GPIO_ACTIVE_HIGH>
>
> the "hdmi-connector" is a big piece of software. It must handle a lot
> of more and more exotic connectors.
> So, I hope that you have written a "simple-hdmi-connector" which does
> nothing but setting the connector type.
> Where is it?

I suddenly thought about something...

If a DVI connector instead of a HDMI connector is soldered, how should such a
device tree be written?

How about solder a HDMI-to-VGA bridge on the board? (Maybe there should be
"dumb-hdmi-dvi-bridge" and "dumb-hdmi-vga-bridge" drivers?)

>
> --
> Ken ar c'hentañ | ** Breizh ha Linux atav! **
> Jef | http://moinejf.free.fr/
>
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