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

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On Thu, Jun 18, 2020 at 9:33 AM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote:
>
> 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.

Okay, understood. I'll look into using DMI matching.

Thanks,
Jeff

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



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