drm/panfrost: Synchronize and disable interrupts before powering off

To make sure that we don't unintentionally perform any unclocked and/or
unpowered R/W operation on GPU registers, before turning off clocks and
regulators we must make sure that no GPU, JOB or MMU ISR execution is
pending: doing that requires to add a mechanism to synchronize the
interrupts on suspend.

Add functions panfrost_{gpu,job,mmu}_suspend_irq() which will perform
interrupts masking and ISR execution synchronization, and then call
those in the panfrost_device_runtime_suspend() handler in the exact
sequence of job (may require mmu!) -> mmu -> gpu.

As a side note, JOB and MMU suspend_irq functions needed some special
treatment: as their interrupt handlers will unmask interrupts, it was
necessary to add an `is_suspended` bitmap which is used to address the
possible corner case of unintentional IRQ unmasking because of ISR
execution after a call to synchronize_irq().

At resume, clear each is_suspended bit in the reset path of JOB/MMU
to allow unmasking the interrupts.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231204114215.54575-4-angelogioacchino.delregno@collabora.com

1 files changed, 22 insertions, 4 deletions

diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index f9446e197428..0c2dbf6ef2a5 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -405,6 +405,8 @@ void panfrost_job_enable_interrupts(struct panfrost_device *pfdev)
 	int j;
 	u32 irq_mask = 0;
 
+	clear_bit(PANFROST_COMP_BIT_JOB, pfdev->is_suspended);
+
 	for (j = 0; j < NUM_JOB_SLOTS; j++) {
 		irq_mask |= MK_JS_MASK(j);
 	}
@@ -413,6 +415,14 @@ void panfrost_job_enable_interrupts(struct panfrost_device *pfdev)
 	job_write(pfdev, JOB_INT_MASK, irq_mask);
 }
 
+void panfrost_job_suspend_irq(struct panfrost_device *pfdev)
+{
+	set_bit(PANFROST_COMP_BIT_JOB, pfdev->is_suspended);
+
+	job_write(pfdev, JOB_INT_MASK, 0);
+	synchronize_irq(pfdev->js->irq);
+}
+
 static void panfrost_job_handle_err(struct panfrost_device *pfdev,
 				    struct panfrost_job *job,
 				    unsigned int js)
@@ -792,17 +802,25 @@ static irqreturn_t panfrost_job_irq_handler_thread(int irq, void *data)
 	struct panfrost_device *pfdev = data;
 
 	panfrost_job_handle_irqs(pfdev);
-	job_write(pfdev, JOB_INT_MASK,
-		  GENMASK(16 + NUM_JOB_SLOTS - 1, 16) |
-		  GENMASK(NUM_JOB_SLOTS - 1, 0));
+
+	/* Enable interrupts only if we're not about to get suspended */
+	if (!test_bit(PANFROST_COMP_BIT_JOB, pfdev->is_suspended))
+		job_write(pfdev, JOB_INT_MASK,
+			  GENMASK(16 + NUM_JOB_SLOTS - 1, 16) |
+			  GENMASK(NUM_JOB_SLOTS - 1, 0));
+
 	return IRQ_HANDLED;
 }
 
 static irqreturn_t panfrost_job_irq_handler(int irq, void *data)
 {
 	struct panfrost_device *pfdev = data;
-	u32 status = job_read(pfdev, JOB_INT_STAT);
+	u32 status;
+
+	if (test_bit(PANFROST_COMP_BIT_JOB, pfdev->is_suspended))
+		return IRQ_NONE;
 
+	status = job_read(pfdev, JOB_INT_STAT);
 	if (!status)
 		return IRQ_NONE;