[alsa-devel] [PATCH 2/2] vgaswitchreoo: set audio client id in vgaswitchreoo enable function

[Lukas Wunner]

On Sat, Jul 14, 2018 at 02:15:24PM +0800, jimqu wrote:
> ??? 2018/7/13 17:27, Lukas Wunner ??????:
> >On Fri, Jul 13, 2018 at 04:06:02PM +0800, Jim Qu wrote:
> >>On modern laptop, there are more and more platforms
> >>have two GPUs, and each of them maybe have audio codec
> >>for HDMP/DP output. For some dGPU which is no output,
> >>audio codec usually is disabled.
> >>
> >>In currect HDA audio driver, it will set all codec as
> >>VGA_SWITCHEROO_DIS, the audio which is binded to UMA
> >>will be suspended if user use debugfs to contorl power
> >>
> >>In HDA driver side, it is difficult to know which GPU
> >>the audio has binded to. So set the bound gpu pci dev
> >>to vgaswitchroo, the correct audio id will be set in
> >>vgaswitchreoo enable function.
> >>
> >>Signed-off-by: Jim Qu <Jim.Qu at amd.com>
> >The approach you've taken in this patch won't work if the HDA controller
> >is bound to a driver after both GPUs have already been bound to a driver
> >and the handler has already been registered.
> >
> >That's because vga_switcheroo_enable() is run when two GPUs have registered
> >as clients and the handler has also registered.  If the HDA controller is
> >probed afterwards, its ID will be stuck at VGA_SWITCHEROO_UNKNOWN_ID.
> 
> In genernic speaking, there are two cases , a. audio client is the third
> client. b. audio client is not the third client.
> 
> if audio is third client. vga_switcheroo_ready() is true,
> vga_switcheroo_enable() can be called in audio client register fuction.
> if audio is not the third client, vga_switcheroo_enable() will be called in
> the second GFX client register.
> In vga_switcheroo_enable() , the first list loop will set two GPU clients'
> id, and the second list loop will select audio client, set id by its bound
> gpu pci dev.

No, if audio is the third client, vga_switcheroo_ready() is *not* true
because vgasr_priv.active is true.  This is set to true once the two
GPUs and the handler have registered.  If the audio device registers
afterwards, vga_switcheroo_enable() will already have been called.
It's never called twice because it sets vgasr_priv.active = true.

As a result, the audio device is stuck at VGA_SWITCHEROO_UNKNOWN_ID.

Thanks,

Lukas