[1/3] drm/i915: Introduce intel_gt_mcr_lock_reset()

Commit Message

Nirmoy Das Sept. 27, 2023, 10:22 a.m. UTC

Implement intel_gt_mcr_lock_reset() to provide a mechanism
for resetting the steer semaphore when absolutely necessary.

Signed-off-by: Nirmoy Das <[e-mail]>
---
 drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 29 ++++++++++++++++++++++++++
 drivers/gpu/drm/i915/gt/intel_gt_mcr.h |  1 +
 2 files changed, 30 insertions(+)

Comments

Andi Shyti Sept. 27, 2023, 11:37 a.m. UTC | #1

Hi Nirmoy,

[...]

> +void intel_gt_mcr_lock_reset(struct intel_gt *gt)
> +{
> +	unsigned long __flags;
> +
> +	lockdep_assert_not_held(&gt->uncore->lock);
> +
> +	spin_lock_irqsave(&gt->mcr_lock, __flags);
> +
> +	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
> +		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
> +
> +	spin_unlock_irqrestore(&gt->mcr_lock, __flags);

As we discussed offline, I don't think spinlocks are needed here.
I don't expect the gt to be holding the lock somewhere else.

Andi

> +}

Nirmoy Das Sept. 27, 2023, 12:36 p.m. UTC | #2

Hi Andi,

On 9/27/2023 1:37 PM, Andi Shyti wrote:
> Hi Nirmoy,
>
> [...]
>
>> +void intel_gt_mcr_lock_reset(struct intel_gt *gt)
>> +{
>> +	unsigned long __flags;
>> +
>> +	lockdep_assert_not_held(&gt->uncore->lock);
>> +
>> +	spin_lock_irqsave(&gt->mcr_lock, __flags);
>> +
>> +	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
>> +		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
>> +
>> +	spin_unlock_irqrestore(&gt->mcr_lock, __flags);
> As we discussed offline, I don't think spinlocks are needed here.
> I don't expect the gt to be holding the lock somewhere else.

I can add a assert but I think it make sense to have the lock just to be 
100% safe ?


Regards,

Nirmoy

>
> Andi
>
>> +}

Patch

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
index bf4a933de03a..d98e0d2fc2ee 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
@@ -419,6 +419,35 @@  void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags)
 		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
 }
 
+/**
+ * intel_gt_mcr_lock_reset - Reset MCR steering lock
+ * @gt: GT structure
+ *
+ * Performs a steer semaphore reset operation. On MTL and beyond, a hardware
+ * lock will also be taken to serialize access not only for the driver,
+ * but also for external hardware and firmware agents.
+ * However, there may be situations where the driver must reset the semaphore
+ * but only when it is absolutely certain that no other agent should own the
+ * lock at that given time.
+ *
+ * Context: Takes gt->mcr_lock.  uncore->lock should *not* be held when this
+ *          function is called, although it may be acquired after this
+ *          function call.
+ */
+void intel_gt_mcr_lock_reset(struct intel_gt *gt)
+{
+	unsigned long __flags;
+
+	lockdep_assert_not_held(&gt->uncore->lock);
+
+	spin_lock_irqsave(&gt->mcr_lock, __flags);
+
+	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
+		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
+
+	spin_unlock_irqrestore(&gt->mcr_lock, __flags);
+}
+
 /**
  * intel_gt_mcr_read - read a specific instance of an MCR register
  * @gt: GT structure
diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.h b/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
index 41684495b7da..485c7711f2e8 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.h
@@ -11,6 +11,7 @@ 
 void intel_gt_mcr_init(struct intel_gt *gt);
 void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags);
 void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags);
+void intel_gt_mcr_lock_reset(struct intel_gt *gt);
 
 u32 intel_gt_mcr_read(struct intel_gt *gt,
 		      i915_mcr_reg_t reg,