On 1/21/2025 10:39 PM, Stephan Gerhold wrote:
On Tue, Jan 21, 2025 at 02:42:41PM +0530, Md Sadre Alam wrote:
This patch resolves a bug from the previous commit where the
BAM_DESC_CNT_TRSHLD register was conditionally written based on BAM-NDP
mode. The issue was reading the BAM_REVISION register hanging if num-ees
was not zero, which occurs when the SoCs power on BAM remotely. So the
BAM_REVISION register read has been moved to inside if condition.
Fixes: 57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing unavailable register")
Reported-by: Georgi Djakov <djakov@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/9ef3daa8-cdb1-49f2-8d19-a72d6210ff3a@xxxxxxxxxx/
Signed-off-by: Md Sadre Alam <quic_mdalam@xxxxxxxxxxx>
I'm afraid there are still two open problems here:
1. In your original commit, you added the if (in_range(...)) checks to
make the BAM_DESC_CNT_TRSHLD register write conditional. With this
patch we only read the bam_revision for the !bdev->num_ees case.
This means that even if we have e.g. a remotely powered BAM-NDP,
we don't initialize BAM_DESC_CNT_TRSHLD anymore.
2. Aside from BAM-NDP and BAM-Lite there is also plain "BAM". You
mentioned we should only skip the register write for BAM-Lite, but
the plain "BAM" isn't handled anywhere yet.
I would recommend inverting the in_range(...) checks to check for if
(!in_range(BAM-LITE) rather than if (in_range(BAM-NDP)). This should
also work for the plain "BAM" type. It will also avoid regressions if we
don't read the bam_revision in the !bdev->num_ees case. (Although
ideally you would lazily initialize the bam_revision to cover all the
configurations.)
Thanks for explanation and suggestion. Will address all the above points
in next revision.
Thanks,
Stephan
---
Change in [v3]
* Revised commit details
Change in [v2]
* Removed unnecessary if checks.
* Relocated the BAM_REVISION register read within the if condition.
Change in [v1]
* https://lore.kernel.org/lkml/1a5fc7e9-39fe-e527-efc3-1ea990bbb53b@xxxxxxxxxxx/
* Posted initial fixup for BAM revision register read handling
drivers/dma/qcom/bam_dma.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index c14557efd577..d227b4f5b6b9 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -1199,11 +1199,11 @@ 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)
--
2.34.1
