Hello Bjorn,
On Fri Feb 7, 2025 at 9:17 PM CET, Bjorn Andersson wrote:
> 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,
Thank you, this fixes the early synchronous external abort in
bam_dma_probe on my msm8916 device.
Tested-by: Sam Day <me@xxxxxxxxxxx>
Regards,
-Sam
