Re: [PATCH 1/2] dmaengine: qcom: bam_dma: Take a PM ref at remove()

[Mostafa Saleh <smostafa@google.com>]

On Tue, Oct 20, 2026 at 01:47:30PM -0500, Frank Li wrote:
> On Tue, Oct 20, 2026 at 06:08:02PM +0000, Mostafa Saleh wrote:
> > [You don't often get email from smostafa@google.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> >
> > bam_dma_remove() calls pm_runtime_dont_use_autosuspend() and
> > pm_runtime_force_suspend(), which on a BAM with its own clock disables
> > bam_clk, and only then writes BAM_IRQ_SRCS_MSK_EE and terminates the
> > channels, touching registers of a block whose clock has just been
> > removed, causing the board to reset.
> >
> > Sashiko(Locally) also reports, it then calls clk_disable_unprepare()
> > on a clock that runtime suspend already disabled, which can trigger
> > "already disabled" warning in clk_core_disable().
> >
> > Hold a runtime PM reference across the register accesses and the
> > channel teardown. Once the hardware is quiet, disable runtime PM with
> > the device still active and drop the clock exactly once, balancing the
> > clk_prepare_enable() in probe.
> >
> > Fixes: 7d2545599f5b ("dmaengine: qcom-bam-dma: Add pm_runtime support")
> > Signed-off-by: Mostafa Saleh <smostafa@google.com>
> > ---
> >  drivers/dma/qcom/bam_dma.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> > index f67a93a37d48..bd583f78e0c1 100644
> > --- a/drivers/dma/qcom/bam_dma.c
> > +++ b/drivers/dma/qcom/bam_dma.c
> > @@ -1403,12 +1403,10 @@ static void bam_dma_remove(struct platform_device *pdev)
> >         struct bam_device *bdev = platform_get_drvdata(pdev);
> >         u32 i;
> >
> > -       pm_runtime_dont_use_autosuspend(&pdev->dev);
> > -       pm_runtime_force_suspend(&pdev->dev);
> > -
> >         of_dma_controller_free(pdev->dev.of_node);
> >         dma_async_device_unregister(&bdev->common);
> >
> > +       pm_runtime_get_sync(&pdev->dev);
> >         /* mask all interrupts for this execution environment */
> >         writel_relaxed(0, bam_addr(bdev, 0,  BAM_IRQ_SRCS_MSK_EE));
> >
> > @@ -1428,6 +1426,9 @@ static void bam_dma_remove(struct platform_device *pdev)
> >
> >         tasklet_kill(&bdev->task);
> >
> > +       pm_runtime_dont_use_autosuspend(&pdev->dev);
> 
> After
> 
> commit d1706f9da9f40dffe8621cc0ee03b847f41f1d6d
> Author: Joshua Crofts <joshua.crofts1@gmail.com>
> Date:   Sat Sep 19 10:24:28 2026 +0200
> 
>     PM: runtime: call pm_runtime_dont_use_autosuspend() on reinit()
> 
>     Add a pm_runtime_dont_use_autosuspend() call to pm_runtime_reinit() to
>     ensure autosuspend is disabled on driver teardown.
> 
>     Suggested-by: Frank Li <Frank.Li@nxp.com>
>     Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
>     Link: https://patch.msgid.link/20260919-move-dont-use-autosuspend-v1-1-f6e2d1315c23@gmail.com
>     Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> 
> Needn't call pm_runtime_dont_use_autosuspend()

I see, thanks for pointing that out, I will remove it in v2.

> 
> 
> > +       pm_runtime_disable(&pdev->dev);
> 
> Can you use devm_pm_*() call to fix this problem.

AFAICT, in that case we need to gate the clk_disable_unprepare()
in remove() as the suspend() also runs after remove(), so
clk_disable() would be called twice.

The problem seems to be bam_dma_runtime_resume/suspend() calling
clk_enable/disable() but also remove() calls disable(), so something
as:

--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -1379,7 +1379,7 @@ static int bam_dma_probe(struct platform_device *pdev)
        pm_runtime_use_autosuspend(&pdev->dev);
        pm_runtime_mark_last_busy(&pdev->dev);
        pm_runtime_set_active(&pdev->dev);
-       pm_runtime_enable(&pdev->dev);
+       devm_pm_runtime_enable(&pdev->dev);
 
        return 0;
 
@@ -1433,9 +1433,10 @@ static void bam_dma_remove(struct platform_device *pdev)
 
        tasklet_kill(&bdev->task);
 
-       pm_runtime_disable(&pdev->dev);
        pm_runtime_put_noidle(&pdev->dev);
+#ifndef CONFIG_PM
        clk_disable_unprepare(bdev->bamclk);
+#endif
 }
 
 static int __maybe_unused bam_dma_runtime_suspend(struct device *dev)


I can see example for both patterns in tree. However, 2) seems to
be more common:
1) Gating CONFIG_PM: drivers/mailbox/mtk-cmdq-mailbox.c
2) Get/disable/put_noidle then clk_disable(): drivers/mmc/host/sdhci-msm.c

Thanks,
Mostafa
> 
> Frank
> > +       pm_runtime_put_noidle(&pdev->dev);
> >         clk_disable_unprepare(bdev->bamclk);
> >  }
> >
> > --
> > 2.56.0.212.g129ede20d9-goog
> >