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

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Message-ID: <20180415190523.GA16129@wunner.de>
Date:   Sun, 15 Apr 2018 21:05:23 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Pali Rohár <pali.rohar@...il.com>
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 Sun, Apr 15, 2018 at 07:17:46PM +0200, Pali Rohár wrote:
> 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.

No, the DRM drivers don't filter ExpressCard-attached GPUs when
registering with vga_switcheroo.  They do filter Thunderbolt-
attached GPUs.

The ExpressCard 2.0 spec defines some ACPI stuff that *might* be
used to recognize root ports that are ExpressCard slots, but I'm
not sure how reliable that is.  I don't have such a machine and
have no experience with it.

This is from the MacBookPro8,3 DSDT:

            Device (RP04)
            {
                Name (_ADR, 0x001C0003)
                OperationRegion (A1E0, PCI_Config, 0x19, 0x01)
                Field (A1E0, ByteAcc, NoLock, Preserve)
                {
                    SECB,   8
                }

                Device (EXCD)
                {
                    Name (_ADR, 0x00)
                    Name (_SUN, 0x01)
                    Method (_RMV, 0, NotSerialized)
                    {
                        Return (0x01)
                    }

                    Name (_EJD, "\\_SB.PCI0.EHC2.HUBN.PRTN.PRT4")
                }
                ...
            }

Thanks,

Lukas