On Mon, Feb 10, 2025 at 09:44:30AM +0100, Stephan Gerhold wrote:
> On Fri, Feb 07, 2025 at 12:17:33PM -0800, 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>
>
> This patch fixes the most critical regression (the bus hang), but the
> in_range(..., BAM_NDP) checks are also wrong. They do not consider the
> plain "BAM" type where the register is apparently also available. The
> check should be !in_range(..., BAM_LITE) instead to fix this.
>
Sorry, I must have not paid sufficient attention while browsing the
replies; and just tried to restore the one case I thought the author
didn't consider...
Thanks for staying on top of it. Revert makes total sense.
Regards,
Bjorn
> I mentioned this twice to Md Sadre Alam [1, 2], but a fix was
> unfortunately never sent for that part of the regression.
>
> I think we should take Caleb's patch and revert the entire patch for the
> 6.14 cycle. There are several incorrect assumptions in the original
> patch, it will be easier to review a fixed version with the full diff,
> rather than looking at incremental fixups.
>
> On a somewhat related note, I'm working on a patch series for bam_dma to
> clean up the handling of remotely controlled BAMs. It will make it more
> clear when it's safe to access BAM registers and when not, and should
> allow reading the revision also for remotely controlled BAMs. This would
> avoid the need for all these if (!bdev->bam_revision) checks.
>
> Thanks,
> Stephan
>
> [1]: https://lore.kernel.org/linux-arm-msm/Z4D2jQNNW94qGIlv@xxxxxxxxxx/
> [2]: https://lore.kernel.org/linux-arm-msm/Z4_U19_QyH2RJvKW@xxxxxxxxxx/
>
> > ---
> > 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>
> >
>
