linux-kernel - Re: [PATCH v3 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics

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Date:   Sun, 15 Apr 2018 19:17:46 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Takashi Iwai <tiwai@...e.de>, mario.limonciello@...l.com,
        andy@...radead.org, dvhart@...radead.org, mjg59@...f.ucam.org,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v3 3/3] ALSA: hda: Disabled unused audio controller for
 Dell platforms with Switchable Graphics

On Saturday 14 April 2018 13:17:11 Lukas Wunner wrote:
> On Sat, Apr 14, 2018 at 12:49:50PM +0200, Pali Rohár wrote:
> > On Saturday 14 April 2018 12:45:12 Lukas Wunner wrote:
> > > On Thu, Apr 12, 2018 at 10:15:41PM +0800, Kai-Heng Feng wrote:
> > > > Do you have any suggestion to check if it connects to the system via
> > > > Thunderbolt?
> > > 
> > > Just use pci_is_thunderbolt_attached(), introduced by 8531e283bee6,
> > > like this:
> > > 
> > > if (check_dell_switchable_gfx(pci) && !pci_is_thunderbolt_attached(pci))
> > 
> > And what about PCI-e device attached to ExpressCard slot?
> 
> I don't know of a bullet-proof way to recognize those.  In theory
> one could check if the PCIe port above the GPU is a non-hotplug
> root port, but I think there are machines with hotplug capable
> root ports with GPUs below them that aren't actually removable.
> 
> However I think ExpressCard-attached GPUs were rare, much less ones
> with integrated HDA controller, so in reality that's probably a
> non-issue.

Hm... maybe another idea: Is it possible to detect which audio pci
device belongs to graphics card via vga_switcheroo? Currently, looking
at output it is same PCI device as graphic card, just different PCI
function.

-- 
Pali Rohár
pali.rohar@...il.com

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