[PATCH v6] pci: prevent putting nvidia GPUs into lower device states on certain intel bridges

[Karol Herbst <kherbst@redhat.com>]

Fixes state transitions of Nvidia Pascal GPUs from D3cold into higher device
states.

v2: convert to pci_dev quirk
    put a proper technical explanation of the issue as a in-code comment
v3: disable it only for certain combinations of intel and nvidia hardware
v4: simplify quirk by setting flag on the GPU itself
v5: restructure quirk to make it easier to add new IDs
    fix whitespace issues
    fix potential NULL pointer access
    update the quirk documentation
v6: move quirk into nouveau

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Mika Westerberg <mika.westerberg@intel.com>
Cc: linux-pci@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=205623
---
 drivers/gpu/drm/nouveau/nouveau_drm.c | 56 +++++++++++++++++++++++++++
 drivers/pci/pci.c                     |  8 ++++
 include/linux/pci.h                   |  1 +
 3 files changed, 65 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 2cd83849600f..51d3a7ba7731 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -618,6 +618,59 @@ nouveau_drm_device_fini(struct drm_device *dev)
 	kfree(drm);
 }
 
+/*
+ * On some Intel PCIe bridge controllers doing a
+ * D0 -> D3hot -> D3cold -> D0 sequence causes Nvidia GPUs to not reappear.
+ * Skipping the intermediate D3hot step seems to make it work again. Thise is
+ * probably caused by not meeting the expectation the involved AML code has
+ * when the GPU is put into D3hot state before invoking it.
+ *
+ * This leads to various manifestations of this issue:
+ *  - AML code execution to power on the GPU hits an infinite loop (as the
+ *    code waits on device memory to change).
+ *  - kernel crashes, as all PCI reads return -1, which most code isn't able
+ *    to handle well enough.
+ *
+ * In all cases dmesg will contain at least one line like this:
+ * 'nouveau 0000:01:00.0: Refused to change power state, currently in D3'
+ * followed by a lot of nouveau timeouts.
+ *
+ * In the \_SB.PCI0.PEG0.PG00._OFF code deeper down writes bit 0x80 to the not
+ * documented PCI config space register 0x248 of the Intel PCIe bridge
+ * controller (0x1901) in order to change the state of the PCIe link between
+ * the PCIe port and the GPU. There are alternative code paths using other
+ * registers, which seem to work fine (executed pre Windows 8):
+ *  - 0xbc bit 0x20 (publicly available documentation claims 'reserved')
+ *  - 0xb0 bit 0x10 (link disable)
+ * Changing the conditions inside the firmware by poking into the relevant
+ * addresses does resolve the issue, but it seemed to be ACPI private memory
+ * and not any device accessible memory at all, so there is no portable way of
+ * changing the conditions.
+ * On a XPS 9560 that means bits [0,3] on \CPEX need to be cleared.
+ *
+ * The only systems where this behavior can be seen are hybrid graphics laptops
+ * with a secondary Nvidia Maxwell, Pascal or Turing GPU. Its unclear wheather
+ * this issue only occurs in combination with listed Intel PCIe bridge
+ * controllers and the mentioned GPUs or other devices as well.
+ *
+ * documentation on the PCIe bridge controller can be found in the
+ * "7th Generation Intel® Processor Families for H Platforms Datasheet Volume 2"
+ * Section "12 PCI Express* Controller (x16) Registers"
+ */
+
+static void quirk_broken_nv_runpm(struct pci_dev *dev)
+{
+	struct pci_dev *bridge = pci_upstream_bridge(dev);
+
+	if (!bridge || bridge->vendor != PCI_VENDOR_ID_INTEL)
+		return;
+
+	switch (bridge->device) {
+	case 0x1901:
+		dev->parent_d3cold = 1;
+	}
+}
+
 static int nouveau_drm_probe(struct pci_dev *pdev,
 			     const struct pci_device_id *pent)
 {
@@ -699,6 +752,7 @@ static int nouveau_drm_probe(struct pci_dev *pdev,
 	if (ret)
 		goto fail_drm_dev_init;
 
+	quirk_broken_nv_runpm(pdev);
 	return 0;
 
 fail_drm_dev_init:
@@ -737,6 +791,8 @@ nouveau_drm_remove(struct pci_dev *pdev)
 {
 	struct drm_device *dev = pci_get_drvdata(pdev);
 
+	/* revert our workaround */
+	pdev->parent_d3cold = false;
 	nouveau_drm_device_remove(dev);
 }
 
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 951099279192..6ece05723fa2 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -860,6 +860,14 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
 	   || (state == PCI_D2 && !dev->d2_support))
 		return -EIO;
 
+	/*
+	 * Power management can be disabled for certain devices as they don't
+	 * come back up later on runtime_resume. We rely on platform means to
+	 * cut power consumption instead (e.g. ACPI).
+	 */
+	if (state != PCI_D0 && dev->parent_d3cold)
+		return 0;
+
 	pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
 	if (pmcsr == (u16) ~0) {
 		pci_err(dev, "can't change power state from %s to %s (config space inaccessible)\n",
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 930fab293073..3e5938b91966 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -340,6 +340,7 @@ struct pci_dev {
 	unsigned int	no_d3cold:1;	/* D3cold is forbidden */
 	unsigned int	bridge_d3:1;	/* Allow D3 for bridge */
 	unsigned int	d3cold_allowed:1;	/* D3cold is allowed by user */
+	unsigned int	parent_d3cold:1;	/* power manage the parent instead */
 	unsigned int	mmio_always_on:1;	/* Disallow turning off io/mem
 						   decoding during BAR sizing */
 	unsigned int	wakeup_prepared:1;
-- 
2.24.1