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SubjectRe: [PATCH v2 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics
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> On Mar 9, 2018, at 5:02 PM, Pali Rohár <pali.rohar@gmail.com> wrote:
>
> On Thursday 08 March 2018 17:10:23 Kai-Heng Feng wrote:
>> Some Dell platforms (Preicsion 7510/7710/7520/7720) have a BIOS option
>> "Switchable Graphics" (SG).
>>
>> When SG is enabled, we have:
>> 00:02.0 VGA compatible controller: Intel Corporation Device 591b (rev 04)
>> 00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31)
>> 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
>> [AMD/ATI] Ellesmere [Polaris10]
>> 01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere
>> [Radeon RX 580]
>>
>> The Intel Audio outputs all the sound, including HDMI audio. The audio
>> controller comes with AMD graphics doesn't get used.
>>
>> When SG is disabled, we have:
>> 00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31)
>> 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
>> [AMD/ATI] Ellesmere [Polaris10]
>> 01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere
>> [Radeon RX 580]
>>
>> Now it's a typical discrete-only system. HDMI audio comes from AMD audio
>> controller, others from Intel audio controller.
>>
>> When SG is enabled, the unused AMD audio controller still exposes its
>> sysfs, so userspace still opens the control file and stream. If
>> userspace tries to output sound through the stream, it hangs when
>> runtime suspend kicks in:
>> [ 12.796265] snd_hda_intel 0000:01:00.1: Disabling via vga_switcheroo
>> [ 12.796367] snd_hda_intel 0000:01:00.1: Cannot lock devices!
>>
>> Since the discrete audio controller isn't useful when SG enabled, we
>> should just disable the device.
>>
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
>> ---
>> v2: Mario suggested to squash the HDA part into the same series.
>>
>> sound/pci/hda/hda_intel.c | 35 +++++++++++++++++++++++++++++++++++
>> 1 file changed, 35 insertions(+)
>>
>> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
>> index 96143df19b21..8e3e8b88624a 100644
>> --- a/sound/pci/hda/hda_intel.c
>> +++ b/sound/pci/hda/hda_intel.c
>> @@ -49,6 +49,7 @@
>> #include <linux/clocksource.h>
>> #include <linux/time.h>
>> #include <linux/completion.h>
>> +#include <linux/dell-common.h>
>>
>> #ifdef CONFIG_X86
>> /* for snoop control */
>> @@ -1620,6 +1621,35 @@ static void check_msi(struct azx *chip)
>> }
>> }
>>
>> +#if IS_ENABLED(CONFIG_DELL_LAPTOP)
>> +static bool check_dell_switchable_gfx(struct pci_dev *pdev)
>> +{
>> + static int (*dell_switchable_gfx_enabled_func)(bool *);
>> + bool enabled;
>> + int err;
>> +
>> + if (pdev->vendor != PCI_VENDOR_ID_ATI ||
>> + pdev->subsystem_vendor != PCI_VENDOR_ID_DELL)
>> + return false;
>
> Are you sure that you want to do this check unconditionally on all
> machines which have enabled CONFIG_DELL_LAPTOP?
>
> Subvendor ID_DELL for dell specific code is not suspicious, but ID_ATI
> is. What would happen if ATI vendor changes to NVIDIA or other which is
> not related to Dell?

We only check it when it's both ATI and DELL, otherwise just return false?

The platform does have a NVIDIA variant, but the discrete NVIDIA have a
audio controller, hence it doesn't have the issue.
The issue only happens to AMD/ATI configs with "Switchable Graphics" option.

>
> Interesting question would be, how handle this situation Windows?

I don't know how this platform handles this on Windows, I guess we need
Mario to shed some lights here.

Kai-Heng

>
>> + dell_switchable_gfx_enabled_func =
>> + symbol_request(dell_switchable_gfx_enabled);
>> + if (!dell_switchable_gfx_enabled_func)
>> + return false;
>> +
>> + err = dell_switchable_gfx_enabled_func(&enabled);
>> +
>> + symbol_put(dell_switchable_gfx_enabled);
>> +
>> + return !err ? enabled : false;
>> +}
>> +#else
>> +static bool check_dell_switchable_gfx(struct pci_dev *pdev)
>> +{
>> + return false;
>> +}
>> +#endif
>> +
>> /* check the snoop mode availability */
>> static void azx_check_snoop_available(struct azx *chip)
>> {
>> @@ -1702,6 +1732,11 @@ static int azx_create(struct snd_card *card,
>> struct pci_dev *pci,
>> if (err < 0)
>> return err;
>>
>> + if (check_dell_switchable_gfx(pci)) {
>> + pci_disable_device(pci);
>> + return -ENODEV;
>> + }
>> +
>> hda = kzalloc(sizeof(*hda), GFP_KERNEL);
>> if (!hda) {
>> pci_disable_device(pci);
>
> --
> Pali Rohár
> pali.rohar@gmail.com

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