Re: [PATCH v5 2/2] media: cec: i2c: ch7322: Add ch7322 CEC controller driver

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On 18/06/2020 18:25, Jeff Chase wrote:
> On Thu, Jun 18, 2020 at 3:05 AM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote:
>>
>> On 18/06/2020 10:59, Jeff Chase wrote:
>>> Hi Hans,
>>>
>>> We are using two of these in an Intel-based Chromebox. I see that the
>>> cros-ec and seco drivers just statically define the PCI BDF of the
>>> Intel graphics device for their boards. I don't see an example of ACPI
>>> passing this information. I can copy cros-ec and seco by adding a
>>> board table and then use the UID of each device to select the correct
>>> port. Adding board-specific configuration to the driver doesn't seem
>>> ideal but I'm not sure what the proper way to pass this using ACPI is.
>>
>> You are right, it's not ACPI, it's using DMI matching.
>>
>> I have zero knowledge about ACPI, so I have no idea if there is some standard
>> method of retrieving this association via ACPI.
> 
> I'm not very familiar with ACPI either. I looked for but did not find
> an ACPI equivalent of_get_mac_address().
> 
> I believe it's possible to reference the PCI node but it would take a
> bit of work on both the coreboot and linux side.
> 
>>
>> This particular chip can actually be used both with DMI matching but also
>> on an ARM with device tree, but since you can't test this on an ARM board,
>> there is no point in adding support for that.
>>
>> However, compared to the cros-ec and seco drivers you can do something a bit
>> different here: those drivers just return -ENODEV if there is no match, but
>> since this driver reads the EDID it can just continue as long as it does not
>> set the CEC_CAP_CONNECTOR_INFO capability.
> 
> Is it necessary to add support if we don't set CEC_CAP_CONNECTOR_INFO?

It is very desirable. Otherwise userspace will not know which CEC device is associated
with which HDMI device. Since you are using two of these chips for a Chromebox, I
suspect that you actually need to support this.

Also, I am (slowly) working on wiring support for this in all CEC transmitter drivers,
so I prefer not to add CEC drivers without support for this.

I really should have noticed much earlier that support for this was missing. My
apologies for that.

Regards,

	Hans



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