vga_switcheroo: Use device link for HDA controller
Back in 2013, runtime PM for GPUs with integrated HDA controller was introduced with commits 0d69704a ("gpu/vga_switcheroo: add driver control power feature. (v3)") and 246efa4a ("snd/hda: add runtime suspend/resume on optimus support (v4)"). Briefly, the idea was that the HDA controller is forced on and off in unison with the GPU. The original code is mostly still in place even though it was never a 100% perfect solution: E.g. on access to the HDA controller, the GPU is powered up via vga_switcheroo_runtime_resume_hdmi_audio() but there are no provisions to keep it resumed until access to the HDA controller has ceased: The GPU autosuspends after 5 seconds, rendering the HDA controller inaccessible. Additionally, a kludge is required when hda_intel.c probes: It has to check whether the GPU is powered down (check_hdmi_disabled()) and defer probing if so. However in the meantime (in v4.10) the driver core has gained a feature called device links which promises to solve such issues in a clean way: It allows us to declare a dependency from the HDA controller (consumer) to the GPU (supplier). The PM core then automagically ensures that the GPU is runtime resumed as long as the HDA controller's ->probe hook is executed and whenever the HDA controller is accessed. By default, the HDA controller has a dependency on its parent, a PCIe Root Port. Adding a device link creates another dependency on its sibling: PCIe Root Port ^ ^ | | | | HDA ===> GPU The device link is not only used for runtime PM, it also guarantees that on system sleep, the HDA controller suspends before the GPU and resumes after the GPU, and on system shutdown the HDA controller's ->shutdown hook is executed before the one of the GPU. It is a complete solution. Using this functionality is as simple as calling device_link_add(), which results in a dmesg entry like this: pci 0000:01:00.1: Linked as a consumer to 0000:01:00.0 The code for the GPU-governed audio power management can thus be removed (except where it's still needed for legacy manual power control). The device link is added in a PCI quirk rather than in hda_intel.c. It is therefore legal for the GPU to runtime suspend to D3cold even if the HDA controller is not bound to a driver or if CONFIG_SND_HDA_INTEL is not enabled, for accesses to the HDA controller will cause the GPU to wake up regardless if they're occurring outside of hda_intel.c (think config space readout via sysfs). Contrary to the previous implementation, the HDA controller's power state is now self-governed, rather than GPU-governed, whereas the GPU's power state is no longer fully self-governed. (The HDA controller needs to runtime suspend before the GPU can.) It is thus crucial that runtime PM is always activated on the HDA controller even if CONFIG_SND_HDA_POWER_SAVE_DEFAULT is set to 0 (which is the default), lest the GPU stays awake. This is achieved by setting the auto_runtime_pm flag on every codec and the AZX_DCAPS_PM_RUNTIME flag on the HDA controller. A side effect is that power consumption might be reduced if the GPU is in use but the HDA controller is not, because the HDA controller is now allowed to go to D3hot. Before, it was forced to stay in D0 as long as the GPU was in use. (There is no reduction in power consumption on my Nvidia GK107, but there might be on other chips.) The code paths for legacy manual power control are adjusted such that runtime PM is disabled during power off, thereby preventing the PM core from resuming the HDA controller. Note that the device link is not only added on vga_switcheroo capable systems, but for *any* GPU with integrated HDA controller. The idea is that the HDA controller streams audio via connectors located on the GPU, so the GPU needs to be on for the HDA controller to do anything useful. This commit implicitly fixes an unbalanced runtime PM ref upon unbind of hda_intel.c: On ->probe, a runtime PM ref was previously released under the condition "azx_has_pm_runtime(chip) || hda->use_vga_switcheroo", but on ->remove a runtime PM ref was only acquired under the first of those conditions. Thus, binding and unbinding the driver twice on a vga_switcheroo capable system caused the runtime PM refcount to drop below zero. The issue is resolved because the AZX_DCAPS_PM_RUNTIME flag is now always set if use_vga_switcheroo is true. For more information on device links please refer to: https://www.kernel.org/doc/html/latest/driver-api/device_link.html Documentation/driver-api/device_link.rst Cc: Dave Airlie <airlied@redhat.com> Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Alex Deucher <alexander.deucher@amd.com> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by:Bjorn Helgaas <bhelgaas@google.com> Reviewed-by:
Takashi Iwai <tiwai@suse.de> Reviewed-by:
Peter Wu <peter@lekensteyn.nl> Tested-by: Kai Heng Feng <kai.heng.feng@canonical.com> # AMD PowerXpress Tested-by: Mike Lothian <mike@fireburn.co.uk> # AMD PowerXpress Tested-by: Denis Lisov <dennis.lissov@gmail.com> # Nvidia Optimus Tested-by: Peter Wu <peter@lekensteyn.nl> # Nvidia Optimus Tested-by: Lukas Wunner <lukas@wunner.de> # MacBook Pro Signed-off-by:
Lukas Wunner <lukas@wunner.de> Link: https://patchwork.freedesktop.org/patch/msgid/51bd38360ff502a8c42b1ebf4405ee1d3f27118d.1520068884.git.lukas@wunner.de
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