Dynamically adding a PCI subfunction

[Christian König]

Am 09.10.2017 um 16:41 schrieb Ilia Mirkin:
> Hello,
>
> As a bit of background, all NVIDIA GPUs since GT215 have an audio
> subfunction for HDMI(/DP) audio to be sent to the sink. This generally
> works.
>
> However some, especially laptop, devices come up with that function
> disabled. We have a quirk to enable it when coming back from runpm,
> but that doesn't help the init case. Basically we have to write a bit
> to the PCI config space:
>
> https://github.com/torvalds/linux/blob/v4.12/drivers/gpu/drm/nouveau/nouveau_drm.c#L783
>
> (MMIO 0x88000 is an alias for the PCI config space)
>
> This works for runtime pm resume, since the device was originally
> there and we just have to make sure the underlying device agrees with
> it, but when it's missing on boot, we have to convince linux that it
> exists, bind a driver, etc.
>
> What's the best way of going about doing that?

Sounds similar to my work about resizing BARs.

I would just try to enable the device and then trigger a rescan of the 
BUS where it is attached (similar to echo 1 > 
/sys/bus/pci/devices/$pci_id_of_your_bus/rescan).

There is certainly a function in the PCI subsystem you just need to call 
for that.

Regards,
Christian.

>
> Thanks,
>
>    -ilia
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