[alsa-devel] [PATCH v2 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics

[Kai Heng Feng]

> On Mar 9, 2018, at 5:02 PM, Pali Rohár <pali.rohar at 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 at 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 at gmail.com