On Fri, Apr 20, 2018 at 12:44 PM, Kai-Heng Feng kai.heng.feng@canonical.com 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