Re: [PATCH 2/2] ALSA: hda: Allow HDA to be runtime suspended when dGPU is not bound

From: Kai-Heng Feng
Date: Wed Aug 28 2019 - 04:25:19 EST

Hi Bjorn,

at 06:31, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:

On Tue, Aug 27, 2019 at 09:47:56PM +0800, Kai-Heng Feng wrote:
It's a common practice to let dGPU unbound and use PCI port PM to
disable its power through _PR3. When the dGPU comes with an HDA
function, the HDA won't be suspended if the dGPU is unbound, so the dGPU
power can't be disabled.

Just a terminology question:

I thought "using PCI port PM" meant using the PCI Power Management
Capability in config space to directly change the device's power
state, e.g., in pci_raw_set_power_state().

What I meant is to use pcieport.ko directly.

And I thought using _PS3, _PR3, etc would be part of "platform power

Ok, will update the wording.

And AFAICT, _PR3 merely returns a list of power resources; it doesn't
disable power itself.

Yes, through its _PS3 and _OFF. Iâll update the wording.


Commit 37a3a98ef601 ("ALSA: hda - Enable runtime PM only for
discrete GPU") only allows HDA to be runtime-suspended once GPU is
bound, to keep APU's HDA working.

However, HDA on dGPU isn't that useful if dGPU is unbound. So let relax
the runtime suspend requirement for dGPU's HDA function, to save lots of

Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
sound/pci/hda/hda_intel.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 99fc0917339b..d4ee070e1a29 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -1285,7 +1285,8 @@ static void init_vga_switcheroo(struct azx *chip)
"Handle vga_switcheroo audio client\n");
hda->use_vga_switcheroo = 1;
- hda->need_eld_notify_link = 1; /* cleared in gpu_bound op */
+ /* cleared in gpu_bound op */
+ hda->need_eld_notify_link = !pci_pr3_present(p);
chip->driver_caps |= AZX_DCAPS_PM_RUNTIME;