[PATCH] dmaengine: qcom: bam_dma: Avoid accessing BAM_REVISION on remote BAM

[Bjorn Andersson]

Commit '57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing
unavailable register")' made this read unconditional, in order to
identify if the instance is BAM-NDP or BAM-Lite.
But the BAM_REVISION register is not accessible on remotely managed BAM
instances and attempts to access it causes the system to crash.

Move the access back to be conditional and expand the checks that was
introduced to restore the old behavior when no revision information is
available.

Fixes: 57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing unavailable register")
Reported-by: Georgi Djakov <djakov@xxxxxxxxxx>
Closes: https://lore.kernel.org/lkml/9ef3daa8-cdb1-49f2-8d19-a72d6210ff3a@xxxxxxxxxx/
Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxxxx>
---
 drivers/dma/qcom/bam_dma.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index c14557efd577..d42d913492a8 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -445,8 +445,8 @@ static void bam_reset(struct bam_device *bdev)
 	writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
 
 	/* set descriptor threshold, start with 4 bytes */
-	if (in_range(bdev->bam_revision, BAM_NDP_REVISION_START,
-		     BAM_NDP_REVISION_END))
+	if (!bdev->bam_revision ||
+	    in_range(bdev->bam_revision, BAM_NDP_REVISION_START, BAM_NDP_REVISION_END))
 		writel_relaxed(DEFAULT_CNT_THRSHLD,
 			       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
 
@@ -1006,8 +1006,8 @@ static void bam_apply_new_config(struct bam_chan *bchan,
 			maxburst = bchan->slave.src_maxburst;
 		else
 			maxburst = bchan->slave.dst_maxburst;
-		if (in_range(bdev->bam_revision, BAM_NDP_REVISION_START,
-			     BAM_NDP_REVISION_END))
+		if (!bdev->bam_revision ||
+		    in_range(bdev->bam_revision, BAM_NDP_REVISION_START, BAM_NDP_REVISION_END))
 			writel_relaxed(maxburst,
 				       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
 	}
@@ -1199,11 +1199,12 @@ static int bam_init(struct bam_device *bdev)
 	u32 val;
 
 	/* read revision and configuration information */
-	val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
-	if (!bdev->num_ees)
+	if (!bdev->num_ees) {
+		val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
 		bdev->num_ees = (val >> NUM_EES_SHIFT) & NUM_EES_MASK;
 
-	bdev->bam_revision = val & REVISION_MASK;
+		bdev->bam_revision = val & REVISION_MASK;
+	}
 
 	/* check that configured EE is within range */
 	if (bdev->ee >= bdev->num_ees)

---
base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
change-id: 20250207-bam-read-fix-2b31297d3fa1

Best regards,
-- 
Bjorn Andersson <bjorn.andersson@xxxxxxxxxxxxxxxx>