[PATCH v2 01/17] drm/msm/a6xx: Use barriers while updating HFI Q headers

[Akhil P Oommen <akhilpo@oss.qualcomm.com>]

To avoid harmful compiler optimizations and IO reordering in the HW, use
barriers and READ/WRITE_ONCE helpers as necessary while accessing the HFI
queue index variables.

Fixes: 4b565ca5a2cb ("drm/msm: Add A6XX device support")
Signed-off-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>
---
 drivers/gpu/drm/msm/adreno/a6xx_hfi.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_hfi.c b/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
index 53cfdf4e6c34..4f5dbf46132b 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
@@ -34,7 +34,7 @@ static int a6xx_hfi_queue_read(struct a6xx_gmu *gmu,
 	struct a6xx_hfi_queue_header *header = queue->header;
 	u32 i, hdr, index = header->read_index;
 
-	if (header->read_index == header->write_index) {
+	if (header->read_index == READ_ONCE(header->write_index)) {
 		header->rx_request = 1;
 		return 0;
 	}
@@ -62,7 +62,10 @@ static int a6xx_hfi_queue_read(struct a6xx_gmu *gmu,
 	if (!gmu->legacy)
 		index = ALIGN(index, 4) % header->size;
 
-	header->read_index = index;
+	/* Ensure all memory operations are complete before updating the read index */
+	dma_mb();
+
+	WRITE_ONCE(header->read_index, index);
 	return HFI_HEADER_SIZE(hdr);
 }
 
@@ -74,7 +77,7 @@ static int a6xx_hfi_queue_write(struct a6xx_gmu *gmu,
 
 	spin_lock(&queue->lock);
 
-	space = CIRC_SPACE(header->write_index, header->read_index,
+	space = CIRC_SPACE(header->write_index, READ_ONCE(header->read_index),
 		header->size);
 	if (space < dwords) {
 		header->dropped++;
@@ -95,7 +98,10 @@ static int a6xx_hfi_queue_write(struct a6xx_gmu *gmu,
 			queue->data[index] = 0xfafafafa;
 	}
 
-	header->write_index = index;
+	/* Ensure all memory operations are complete before updating the write index */
+	dma_mb();
+
+	WRITE_ONCE(header->write_index, index);
 	spin_unlock(&queue->lock);
 
 	gmu_write(gmu, REG_A6XX_GMU_HOST2GMU_INTR_SET, 0x01);

-- 
2.51.0