APPLIED[C/Unstable]: [SRU][Bionic][OEM-B][PATCH v2 0/6] HDMI/DP audio can't work on the laptop of Dell Latitude 5495

Seth Forshee seth.forshee at
Wed Aug 1 13:11:51 UTC 2018

On Mon, Jul 30, 2018 at 09:32:18AM +0800, Hui Wang wrote:
> BugLink:
> In the v2:
> the patchset is also sent to OEM-B since the OEM project is waiting for the patchset.
> The v1 introduced a building error, my investigation is shown as below:
> The declaration of "enum vga_switcheroo_client_id (*get_client_id)(struct pci_dev *pdev);"
> and the implementation of "static int nouveau_dsm_get_client_id(struct pci_dev *pdev)"
> exist in the kernel (bionic, artful) for a long time, but "-Werror=incompatible-pointer-types"
> didn't report it as an error, after applied these 2 patches, it is reported as an error,
> that is because the patch touches the definition of "enum vga_switcheroo_client_id",
> before applying these 2 patches, the vga_switcheroo_client_id includes a negative numer:
> VGA_SWITCHEROO_UNKNOWN_ID = -1, but after applying the patches, there is no negative number
> anymore in the "enum vga_swicheroo_client_id".
> I guess if the definition of enum includes negative number, the c compiler treat it as int type,
> that is why artful and bionic did not expose building error before.
> To fix the building error, I cherry-picked 4 more patches [3/6-6/6], and the purpose of those
> 4 patches is straightforward.
> In the v1:
> This bug comes from the OEM project, and the engineer Jim Qu from AMD took
> almost 2 weeks to investigate this problem, then he worte these two patches to
> fix this problem and now the patches are merged to sound repository.
> According to Jim Qu's investigation, the root cause of this problem is:
> 1. there is two GPU on the system. iGPU has a audio codec for HDMI output,
>    and dGPU is without audio codec it is only for offload rendering.
> 2. under runtime pm, when dGPU suspend, amdgpu will also call vgaswitchroo
>    driver to power off audio which vgaswitchroo client is VGA_SWITCHEROO_DIS.
> 3. In current HDA audio driver, the iGPU's audio will register to vgaswitchroo
>    as VGA_SWITCHEROO_DIS, therefore, the audio will be selected and powered off
>    by runtime pm.
> [Impact]
> On the Dell Latitude 5495, If we plug a monitor with audio capability to the
> HDMI/DP ports, we can't find HDMI/DP audio sinks as expected, then we can't
> play any sound through HDMI/DP audio.
> [Fix]
> With these two patches, the driver will not always set vgaswicheroo clients of
> HDA audio as VGA_SWITCHEROO_DIS, it will set it to _DIS or _IGD with the help
> of callback function of DRM drivers. So on this machine, the vgaswicheroo client
> will be set _IGD, then it will not be powered off when discrete gpu is powered off. 
> [Test Case]
> We tested plug/unplug detection and playback through HDMI/DP audio, everything works
> well.
> [Regression Potential]
> Very low, without these two patches, the vgaswitchroo client of audio will be
> set to _DIS unconditionally, it did not expose any problem because in the past,
> all the HDMI/DP audio codecs are in the discreate GPU. But on Latitude 5495, the
> HDMI/DP audio codec is in the integrated GPU, so we need to change the driver to
> let DRM driver decide if it is _DIS or _IGD, it will not introduce regression for
> old mahcines on old machines, the client will be set to _DIS as before.
> And we have tested these two patches on some old machines with two gpus like A+A
> , I+A and I+N, all of them worked well as before.
> Jim Qu (2):
>   vga_switcheroo: set audio client id according to bound GPU id
> Luc Van Oostenryck (4):
>   drm/nouveau: fix nouveau_dsm_get_client_id()'s return type
>   drm/radeon: fix radeon_atpx_get_client_id()'s return type
>   drm/amdgpu: fix amdgpu_atpx_get_client_id()'s return type
>   platform/x86: apple-gmux: fix gmux_get_client_id()'s return type
>  drivers/gpu/drm/amd/amdgpu/amdgpu_atpx_handler.c |  2 +-
>  drivers/gpu/drm/nouveau/nouveau_acpi.c           |  2 +-
>  drivers/gpu/drm/radeon/radeon_atpx_handler.c     |  2 +-
>  drivers/gpu/vga/vga_switcheroo.c                 | 62 +++++++++++++++++++-----
>  drivers/platform/x86/apple-gmux.c                |  2 +-
>  include/linux/vga_switcheroo.h                   |  8 +--
>  sound/pci/hda/hda_intel.c                        | 13 ++---
>  7 files changed, 66 insertions(+), 25 deletions(-)

Applied to cosmic/master-next, with the backport for "vga_switcheroo:
set audio client id according to bound GPU id" replaced with a cherry
pick from the maintainer tree. Also applied that patch and "ALSA: hda:
unstable/master, as the other patches are already in 4.18. Thanks!

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