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-rw-r--r--debian/patches-rt/0061-drm-i915-Do-not-disable-preemption-for-resets.patch110
1 files changed, 110 insertions, 0 deletions
diff --git a/debian/patches-rt/0061-drm-i915-Do-not-disable-preemption-for-resets.patch b/debian/patches-rt/0061-drm-i915-Do-not-disable-preemption-for-resets.patch
new file mode 100644
index 000000000..db8400741
--- /dev/null
+++ b/debian/patches-rt/0061-drm-i915-Do-not-disable-preemption-for-resets.patch
@@ -0,0 +1,110 @@
+From 1d651fe6c67cb3b355cc228f75289657496520ff Mon Sep 17 00:00:00 2001
+From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
+Date: Fri, 18 Aug 2023 22:45:25 -0400
+Subject: [PATCH 61/62] drm/i915: Do not disable preemption for resets
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.69-rt21.tar.xz
+
+[commit 40cd2835ced288789a685aa4aa7bc04b492dcd45 in linux-rt-devel]
+
+Commit ade8a0f59844 ("drm/i915: Make all GPU resets atomic") added a
+preempt disable section over the hardware reset callback to prepare the
+driver for being able to reset from atomic contexts.
+
+In retrospect I can see that the work item at a time was about removing
+the struct mutex from the reset path. Code base also briefly entertained
+the idea of doing the reset under stop_machine in order to serialize
+userspace mmap and temporary glitch in the fence registers (see
+eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex"),
+but that never materialized and was soon removed in 2caffbf11762
+("drm/i915: Revoke mmaps and prevent access to fence registers across
+reset") and replaced with a SRCU based solution.
+
+As such, as far as I can see, today we still have a requirement that
+resets must not sleep (invoked from submission tasklets), but no need to
+support invoking them from a truly atomic context.
+
+Given that the preemption section is problematic on RT kernels, since the
+uncore lock becomes a sleeping lock and so is invalid in such section,
+lets try and remove it. Potential downside is that our short waits on GPU
+to complete the reset may get extended if CPU scheduling interferes, but
+in practice that probably isn't a deal breaker.
+
+In terms of mechanics, since the preemption disabled block is being
+removed we just need to replace a few of the wait_for_atomic macros into
+busy looping versions which will work (and not complain) when called from
+non-atomic sections.
+
+Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
+Cc: Chris Wilson <chris.p.wilson@intel.com>
+Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
+Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Link: https://lore.kernel.org/r/20230705093025.3689748-1-tvrtko.ursulin@linux.intel.com
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+[PG: backport from v6.4-rt ; minor context fixup caused by b7d70b8b06ed]
+Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
+Signed-off-by: Clark Williams <williams@redhat.com>
+---
+ drivers/gpu/drm/i915/gt/intel_reset.c | 12 +++++-------
+ 1 file changed, 5 insertions(+), 7 deletions(-)
+
+diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
+index 10b930eaa8cb..6108a449cd19 100644
+--- a/drivers/gpu/drm/i915/gt/intel_reset.c
++++ b/drivers/gpu/drm/i915/gt/intel_reset.c
+@@ -174,13 +174,13 @@ static int i915_do_reset(struct intel_gt *gt,
+ /* Assert reset for at least 20 usec, and wait for acknowledgement. */
+ pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
+ udelay(50);
+- err = wait_for_atomic(i915_in_reset(pdev), 50);
++ err = _wait_for_atomic(i915_in_reset(pdev), 50, 0);
+
+ /* Clear the reset request. */
+ pci_write_config_byte(pdev, I915_GDRST, 0);
+ udelay(50);
+ if (!err)
+- err = wait_for_atomic(!i915_in_reset(pdev), 50);
++ err = _wait_for_atomic(!i915_in_reset(pdev), 50, 0);
+
+ return err;
+ }
+@@ -200,7 +200,7 @@ static int g33_do_reset(struct intel_gt *gt,
+ struct pci_dev *pdev = to_pci_dev(gt->i915->drm.dev);
+
+ pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
+- return wait_for_atomic(g4x_reset_complete(pdev), 50);
++ return _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
+ }
+
+ static int g4x_do_reset(struct intel_gt *gt,
+@@ -217,7 +217,7 @@ static int g4x_do_reset(struct intel_gt *gt,
+
+ pci_write_config_byte(pdev, I915_GDRST,
+ GRDOM_MEDIA | GRDOM_RESET_ENABLE);
+- ret = wait_for_atomic(g4x_reset_complete(pdev), 50);
++ ret = _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
+ if (ret) {
+ GT_TRACE(gt, "Wait for media reset failed\n");
+ goto out;
+@@ -225,7 +225,7 @@ static int g4x_do_reset(struct intel_gt *gt,
+
+ pci_write_config_byte(pdev, I915_GDRST,
+ GRDOM_RENDER | GRDOM_RESET_ENABLE);
+- ret = wait_for_atomic(g4x_reset_complete(pdev), 50);
++ ret = _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
+ if (ret) {
+ GT_TRACE(gt, "Wait for render reset failed\n");
+ goto out;
+@@ -718,9 +718,7 @@ int __intel_gt_reset(struct intel_gt *gt, intel_engine_mask_t engine_mask)
+ intel_uncore_forcewake_get(gt->uncore, FORCEWAKE_ALL);
+ for (retry = 0; ret == -ETIMEDOUT && retry < retries; retry++) {
+ GT_TRACE(gt, "engine_mask=%x\n", engine_mask);
+- preempt_disable();
+ ret = reset(gt, engine_mask, retry);
+- preempt_enable();
+ }
+ intel_uncore_forcewake_put(gt->uncore, FORCEWAKE_ALL);
+
+--
+2.43.0
+