Re: [PATCH] dmaengine: pl330: drop only the runtime PM reference a channel holds

[Krzysztof Sokołowski]

W dniu 28.10.2026 o 15:35, Frank Li pisze:
> On Wed, Oct 28, 2026 at 12:28:11PM +0100, Krzysztof Sokołowski via B4 Relay wrote:
> > [You don't often get email from devnull+krzysiek.sokolowski.gmail.com@xxxxxxxxxx. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> >
> > From: Krzysztof Sokołowski <krzysiek.sokolowski@xxxxxxxxx>
> >
> > pl330_tasklet() drops a runtime PM reference when the channel's work
> > list is empty, without checking that the channel still holds one.
> > pl330_terminate_all() drops that reference too (power_down =
> > pch->active) and clears pch->active. If a completion schedules the
> > tasklet and a client terminates the channel before the tasklet runs, the
> > tasklet finds an empty work list and drops the reference a second time:
> >
> >    Runtime PM usage count underflow!
> >
> > after which the controller can be runtime suspended while still in use.
> >
> > Seen on an RK3128 board (dw_mmc using the PL330 for SD transfers) under
> > combined SD and USB load, where the dw_mmc error path terminates the
> > channel; the underflow was followed by "pl330_update:1678 Unexpected!"
> > and a failure to request the DMA channel again.
> >
> > Take power_down from pch->active in the tasklet, as pl330_terminate_all()
> > does, so the reference taken in pl330_issue_pending() is dropped once.
> >
> > Fixes: 5c9e6c2b2ba3 ("dmaengine: pl330: Fix runtime PM support for terminated transfers")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Krzysztof Sokołowski <krzysiek.sokolowski@xxxxxxxxx>
> > ---
> The same patch at
> https://patchwork.kernel.org/project/linux-dmaengine/patch/20261015-review-pl330-pm-original-v3-v3-1-5be09f37df77@xxxxxxxxxxx/
>
> Frank
> >   drivers/dma/pl330.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> > index c2d0b47..b0eced8 100644
> > --- a/drivers/dma/pl330.c
> > +++ b/drivers/dma/pl330.c
> > @@ -2090,7 +2090,12 @@ static void pl330_tasklet(struct tasklet_struct *t)
> >                  spin_lock(&pch->thread->dmac->lock);
> >                  _stop(pch->thread);
> >                  spin_unlock(&pch->thread->dmac->lock);
> > -               power_down = true;
> > +               /*
> > +                * Drop the runtime PM reference only if this channel still
> > +                * holds it: pl330_terminate_all() may already have dropped it
> > +                * while this tasklet was scheduled.
> > +                */
> > +               power_down = pch->active;
> >                  pch->active = false;
> >          } else {
> >                  /* Make sure the PL330 Channel thread is active */
> >
> > ---
> > base-commit: aff5e6a77fc69a7c490246465940d18422d7c631
> > change-id: 20261028-pl330-runtime-pm-b5a30050b2f5
> >
> > Best regards,
> > --
> > Krzysztof Sokołowski <krzysiek.sokolowski@xxxxxxxxx>
Hello.

It is very interesting, but I have it for last month only in my private 
repo, that has now public facing side to upstream fixes I have made .

My public repo: https://github.com/ksokolowski/rocknix-distribution/

Set of patches including this one are here:

https://github.com/ksokolowski/rocknix-distribution/commit/dd3923788d94588b8d5fdb602808b13370ab4208#diff-27b400675ba20f118e98f9a25b963ece2a2336d9ef1fc9416c273f507e24c271

Anyway, I can confirm it works fine on real hardware for last month. So 
you can drop my patch and merge previous one as tested and confirmed to 
work.

Krzysztof