2024-01-22 17:57:19 +01:00
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From e55c680ca3b29815a9cf95135011b72fb216b57b Mon Sep 17 00:00:00 2001
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2024-01-04 13:38:55 +01:00
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From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
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Date: Fri, 18 Aug 2023 22:45:25 -0400
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Subject: [PATCH 61/62] drm/i915: Do not disable preemption for resets
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[commit 40cd2835ced288789a685aa4aa7bc04b492dcd45 in linux-rt-devel]
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Commit ade8a0f59844 ("drm/i915: Make all GPU resets atomic") added a
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preempt disable section over the hardware reset callback to prepare the
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driver for being able to reset from atomic contexts.
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In retrospect I can see that the work item at a time was about removing
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the struct mutex from the reset path. Code base also briefly entertained
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the idea of doing the reset under stop_machine in order to serialize
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userspace mmap and temporary glitch in the fence registers (see
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eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex"),
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but that never materialized and was soon removed in 2caffbf11762
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("drm/i915: Revoke mmaps and prevent access to fence registers across
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reset") and replaced with a SRCU based solution.
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As such, as far as I can see, today we still have a requirement that
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resets must not sleep (invoked from submission tasklets), but no need to
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support invoking them from a truly atomic context.
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Given that the preemption section is problematic on RT kernels, since the
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uncore lock becomes a sleeping lock and so is invalid in such section,
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lets try and remove it. Potential downside is that our short waits on GPU
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to complete the reset may get extended if CPU scheduling interferes, but
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in practice that probably isn't a deal breaker.
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In terms of mechanics, since the preemption disabled block is being
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removed we just need to replace a few of the wait_for_atomic macros into
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busy looping versions which will work (and not complain) when called from
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non-atomic sections.
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Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
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Cc: Chris Wilson <chris.p.wilson@intel.com>
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Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
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Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Link: https://lore.kernel.org/r/20230705093025.3689748-1-tvrtko.ursulin@linux.intel.com
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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[PG: backport from v6.4-rt ; minor context fixup caused by b7d70b8b06ed]
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Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
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Signed-off-by: Clark Williams <williams@redhat.com>
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---
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drivers/gpu/drm/i915/gt/intel_reset.c | 12 +++++-------
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1 file changed, 5 insertions(+), 7 deletions(-)
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diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
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index 10b930eaa8cb..6108a449cd19 100644
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--- a/drivers/gpu/drm/i915/gt/intel_reset.c
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+++ b/drivers/gpu/drm/i915/gt/intel_reset.c
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@@ -174,13 +174,13 @@ static int i915_do_reset(struct intel_gt *gt,
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/* Assert reset for at least 20 usec, and wait for acknowledgement. */
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pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
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udelay(50);
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- err = wait_for_atomic(i915_in_reset(pdev), 50);
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+ err = _wait_for_atomic(i915_in_reset(pdev), 50, 0);
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/* Clear the reset request. */
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pci_write_config_byte(pdev, I915_GDRST, 0);
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udelay(50);
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if (!err)
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- err = wait_for_atomic(!i915_in_reset(pdev), 50);
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+ err = _wait_for_atomic(!i915_in_reset(pdev), 50, 0);
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return err;
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}
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@@ -200,7 +200,7 @@ static int g33_do_reset(struct intel_gt *gt,
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struct pci_dev *pdev = to_pci_dev(gt->i915->drm.dev);
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pci_write_config_byte(pdev, I915_GDRST, GRDOM_RESET_ENABLE);
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- return wait_for_atomic(g4x_reset_complete(pdev), 50);
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+ return _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
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}
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static int g4x_do_reset(struct intel_gt *gt,
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@@ -217,7 +217,7 @@ static int g4x_do_reset(struct intel_gt *gt,
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pci_write_config_byte(pdev, I915_GDRST,
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GRDOM_MEDIA | GRDOM_RESET_ENABLE);
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- ret = wait_for_atomic(g4x_reset_complete(pdev), 50);
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+ ret = _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
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if (ret) {
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GT_TRACE(gt, "Wait for media reset failed\n");
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goto out;
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@@ -225,7 +225,7 @@ static int g4x_do_reset(struct intel_gt *gt,
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pci_write_config_byte(pdev, I915_GDRST,
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GRDOM_RENDER | GRDOM_RESET_ENABLE);
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- ret = wait_for_atomic(g4x_reset_complete(pdev), 50);
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+ ret = _wait_for_atomic(g4x_reset_complete(pdev), 50, 0);
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if (ret) {
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GT_TRACE(gt, "Wait for render reset failed\n");
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goto out;
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@@ -718,9 +718,7 @@ int __intel_gt_reset(struct intel_gt *gt, intel_engine_mask_t engine_mask)
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intel_uncore_forcewake_get(gt->uncore, FORCEWAKE_ALL);
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for (retry = 0; ret == -ETIMEDOUT && retry < retries; retry++) {
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GT_TRACE(gt, "engine_mask=%x\n", engine_mask);
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- preempt_disable();
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ret = reset(gt, engine_mask, retry);
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- preempt_enable();
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}
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intel_uncore_forcewake_put(gt->uncore, FORCEWAKE_ALL);
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--
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2.43.0
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