On Fri, Apr 20, 2018 at 12:44 PM, Kai-Heng Feng
<kai.heng.feng@xxxxxxxxxxxxx> 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 contoller still exposes its
> sysfs, so userspace still opens the control file and stream. If
> userspace tries to output sound through the stream, it hangs the system.
>
> Since the discrete audio controller isn't useful when SG is enabled, we
> should just disable the device.
> +static bool check_dell_switchable_gfx(struct pci_dev *pdev)
Yeah, as following existing naming scheme in the driver
(check_hdmi_disabled(), for example)
I would rather call it similar:
check_switchable_gfx_enabled()
> +{
> + bool (*dell_switchable_gfx_is_enabled_func)(void);
> + bool enabled;
> +
> + /* Thunderbolt devices won't be switchable */
> + if (pci_is_thunderbolt_attached(pdev))
> + return false;
> +
> + /* Only check for Dell laptops and AIOs */
> + if (!dmi_find_device(DMI_DEV_TYPE_OEM_STRING, "Dell System", NULL) ||
> + !(dmi_match(DMI_CHASSIS_TYPE, "10") ||
> + dmi_match(DMI_CHASSIS_TYPE, "13")) ||
Can't we do it in more flexible way, i.e. using struct dmi_system_id
table and dmi_check_system() ?
> + !(pdev->vendor == PCI_VENDOR_ID_ATI ||
> + pdev->vendor == PCI_VENDOR_ID_NVIDIA))
> + return false;
I would rather split DMI and PCI checks.
> +
> + dell_switchable_gfx_is_enabled_func =
> + symbol_request(dell_switchable_gfx_is_enabled);
> + if (!dell_switchable_gfx_is_enabled_func)
> + return false;
> +
> + enabled = dell_switchable_gfx_is_enabled_func();
> +
> + symbol_put(dell_switchable_gfx_is_enabled);
> +
> + return enabled;
> +}
> +#else
> +static bool check_dell_switchable_gfx(struct pci_dev *pdev)
inline
> +{
> + return false;
> +}
> +#endif
--
With Best Regards,
Andy Shevchenko
