Am 09.10.2017 um 17:57 schrieb Ilia Mirkin:
On Mon, Oct 9, 2017 at 11:45 AM, Christian König
<ckoenig.leichtzumerken@xxxxxxxxx> wrote:
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.
I'm not exactly familiar with the pci subsystem. I know that hotplug
is a thing, at least in theory. I figured it'd be something related to
that, since this is in essence a random device appearing on the bus
after the initial scan. Is a bus rescan safe on a fully initialized
system?
Either way, some specific functions to call or look at would be great.
Well I would just try to use pci_rescan_bus(), as far as I know that
should be save even when devices are already configured.
Christian.
Cheers,
-ilia
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