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

[Laurent Pinchart]

On Thursday 01 Dec 2016 12:30:09 Jean-Francois Moine wrote:
> On Thu, 01 Dec 2016 12:41:20 +0200 Laurent Pinchart wrote:
> >>> If a DVI connector instead of a HDMI connector is soldered, how
> >>> should such a device tree be written?
> >> 
> >> Use a dvi-connector instead :)
> > 
> > The HDMI encoder DT node doesn't (and certainly shouldn't) report what
> > type of connector is mounted on the board. Having a connector node in DT
> > makes the connector type available to the system, allowing the DRM driver
> > to expose the right connector type to userspace (it would be confusing
> > for the user to report DRM_MODE_CONNECTOR_HDMIA for a DVI connector).
> 
> The connector type, HDMI or DVI, is known by the EDID.
> The user is not interested by the software indication of the connector
> type: (s)he knows it because (s)he connected him/herself the display
> device.

That's not correct. The connector type reported by DRM to userspace can be 
used as a hint to information the user about connectors. Displaying a "Please 
connect a monitor to the HDMI connector" is confusing when the system has a 
DVI connector.

> And the DRM driver does not do anything from the knowledge of the
> connector type in the DT. Only the EDID may tell if the display device
> may do audio streaming (direct HDMI with audio capability) or not
> (direct HDMI without audio, HDMI to DVI cable, DVI physical connector).

-- 
Regards,

Laurent Pinchart

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

[Laurent Pinchart]

On Thursday 01 Dec 2016 09:55:20 Maxime Ripard wrote:
> On Thu, Dec 01, 2016 at 01:33:30AM +0800, Icenowy Zheng wrote:
> >>>  hdmi-out {
> >>>  compatible = "hdmi-connector";
> >>>  type = "a";
> >>>  /* I2C bus and GPIO references are made up for the
> >>> example */ ddc-i2c-bus = <>;
> >>>  hpd-gpios = < 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?
> 
> Use a dvi-connector instead :)

The HDMI encoder DT node doesn't (and certainly shouldn't) report what type of 
connector is mounted on the board. Having a connector node in DT makes the 
connector type available to the system, allowing the DRM driver to expose the 
right connector type to userspace (it would be confusing for the user to 
report DRM_MODE_CONNECTOR_HDMIA for a DVI connector).

> > 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?)
> 
> It probably wouldn't be dumb, but yeah, it would definitely be a
> bridge instead of the connector.

-- 
Regards,

Laurent Pinchart

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

[Jean-Francois Moine]

On Thu, 01 Dec 2016 12:41:20 +0200
Laurent Pinchart  wrote:

> > > If a DVI connector instead of a HDMI connector is soldered, how
> > > should such a device tree be written?
> > 
> > Use a dvi-connector instead :)
> 
> The HDMI encoder DT node doesn't (and certainly shouldn't) report what type 
> of 
> connector is mounted on the board. Having a connector node in DT makes the 
> connector type available to the system, allowing the DRM driver to expose the 
> right connector type to userspace (it would be confusing for the user to 
> report DRM_MODE_CONNECTOR_HDMIA for a DVI connector).

The connector type, HDMI or DVI, is known by the EDID.
The user is not interested by the software indication of the connector
type: (s)he knows it because (s)he connected him/herself the display
device.
And the DRM driver does not do anything from the knowledge of the
connector type in the DT. Only the EDID may tell if the display device
may do audio streaming (direct HDMI with audio capability) or not
(direct HDMI without audio, HDMI to DVI cable, DVI physical connector).

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

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

[Maxime Ripard]

On Thu, Dec 01, 2016 at 01:33:30AM +0800, Icenowy Zheng wrote:
> >>          hdmi-out {
> >>                  compatible = "hdmi-connector";
> >>                  type = "a";
> >>                  /* I2C bus and GPIO references are made 
> >> up for the example */
> >>                  ddc-i2c-bus = <>;
> >>                  hpd-gpios = < 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?

Use a dvi-connector instead :)

> 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?)

It probably wouldn't be dumb, but yeah, it would definitely be a
bridge instead of the connector.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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[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" :
> On Wed, 30 Nov 2016 11:52:25 +0200
> Laurent Pinchart  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 = <_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 = <>;
>>                  hpd-gpios = < 7 GPIO_ACTIVE_HIGH>
>>
>>                  port {
>>                          hdmi_con: endpoint {
>>                                  
>> remote-endpoint = <_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 = <>;
>>                  hpd-gpios = < 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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[linux-sunxi] Re: [PATCH v7 4/8] drm/sunxi: Add DT bindings documentation of Allwinner HDMI

[Icenowy Zheng]

30.11.2016, 17:28, "Jean-Francois Moine" :
> 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 */
>>
>>          hdmi at 39 {
>>                  compatible = "adi,adv7511w";
>>                  reg = <0x39>;
>>                  interrupt-parent = <>;
>>                  interrupts = <29 IRQ_TYPE_LEVEL_LOW>;
>>
>>                  adi,input-depth = <8>;
>>                  adi,input-colorspace = "rgb";
>>                  adi,input-clock = "1x";
>>                  adi,input-style = <1>;
>>                  adi,input-justification = "evenly";
>>
>>                  ports {
>>                          #address-cells = <1>;
>>                          #size-cells = <0>;
>>
>>                          port at 0 {
>>                                  reg = <0>;
>>                                  
>> adv7511_in: endpoint {
>>                                       
>>    remote-endpoint = <_out_rgb>;
>>                                  };
>>                          };
>>
>>                          port at 1 {
>>                                  reg = <1>;
>>                                  
>> adv7511_out: endpoint {
>>                                       
>>    remote-endpoint = <_con>;
>>                                  };
>>                          };
>>                  };
>>          };
>>
>>          /* HDMI connector */
>>
>>          hdmi-out {
>>                  compatible = "hdmi-connector";
>>                  type = "a";
>>
>>                  port {
>>                          hdmi_con: endpoint {
>>                                  
>> remote-endpoint = <_out>;
>>                          };
>>                  };
>>          };
>
> Hi Laurent,
>
> Sorry for I don't see the interest:
> - it is obvious that the HDMI connector is a 'hdmi-connector'!

Yes, it means the wire between the HDMI pins on the SoC and the connector ;-)

> - the physical connector type may be changed on any board by a soldering
>   iron or a connector to connector cable.

I can always alter the devices on a board ;-)

But I should also alter the dt after altering the board.

> - what does the software do with the connector type?
> - why not to put the connector information in the HDMI device?
>
> And, if I follow you, the graph of ports could also be used to describe
> the way the various parts of the SoCs are powered, to describe the pin
> connections, to describe the USB connectors, to describe the board
> internal hubs and bridges...
>
> --
> Ken ar c'hentañ | ** Breizh ha Linux atav! **
> Jef | http://moinejf.free.fr/
>
> --
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