[Intel-gfx] [PATCH] drm/i915: Allow D3 when we are not actively managing a known PCI device.

[Rodrigo Vivi]

The force_probe protection actively avoids the probe of i915 to
manage a device that is currently under development. It is a nice
protection for future users when getting a new platform but using
some older kernel.

However, when we avoid the probe we don't take back the registration
of the device. We cannot give up the registration anyway since we can
have multiple devices present. For instance an integrated and a discrete
one.

When this scenario occurs, the user will not be able to change any
of the runtime pm configuration of the unmanaged device. So, it will
be blocked in D0 state wasting power. This is specially bad in the
case where we have a discrete platform attached, but the user is
able to fully use the integrated one for everything else.

So, let's put the protected and unmanaged device in D3. So we can
save some power.

Reported-by: Daniel J Blueman <daniel at quora.org>
Cc: stable at vger.kernel.org
Cc: Daniel J Blueman <daniel at quora.org>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Anshuman Gupta <anshuman.gupta at intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/i915/i915_pci.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
index 77e7df21f539..fc3e7c69af2a 100644
--- a/drivers/gpu/drm/i915/i915_pci.c
+++ b/drivers/gpu/drm/i915/i915_pci.c
@@ -25,6 +25,7 @@
 #include <drm/drm_color_mgmt.h>
 #include <drm/drm_drv.h>
 #include <drm/i915_pciids.h>
+#include <linux/pm_runtime.h>
 
 #include "gt/intel_gt_regs.h"
 #include "gt/intel_sa_media.h"
@@ -1304,6 +1305,7 @@ static int i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
 	struct intel_device_info *intel_info =
 		(struct intel_device_info *) ent->driver_data;
+	struct device *kdev = &pdev->dev;
 	int err;
 
 	if (intel_info->require_force_probe &&
@@ -1314,6 +1316,12 @@ static int i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 			 "module parameter or CONFIG_DRM_I915_FORCE_PROBE=%04x configuration option,\n"
 			 "or (recommended) check for kernel updates.\n",
 			 pdev->device, pdev->device, pdev->device);
+
+		/* Let's not waste power if we are not managing the device */
+		pm_runtime_use_autosuspend(kdev);
+		pm_runtime_allow(kdev);
+		pm_runtime_put_autosuspend(kdev);
+
 		return -ENODEV;
 	}
 
-- 
2.37.2