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SubjectRe: [PATCH v2 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics
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?

Interesting question would be, how handle this situation Windows?

> + 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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