Re: [PATCH 2/4] dmaengine: ti: cppi41: Fix register access in suspend_late

[Frank Li]

On Tue, Nov 03, 2026 at 08:37:29PM +0100, Markus Schneider-Pargmann (TI) wrote:
> [You don't often get email from msp@xxxxxxxxxxxx. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> cppi41_suspend() and cppi41_resume() access registers. However the
> device may be runtime suspended in which case it is not allowed to
> access the registers.
>
> On suspend do not run disable_sched() when it is runtime suspended. This
> avoids accessing the registers and crashing the kernel during suspend.
>
> Resume when runtime suspended is delayed until cppi41_runtime_resume()
> is called using the variable ctx_lost. This keeps any access while the
> device is runtime suspended.
>
> Fixes: fdea2d09b997 ("dmaengine: cppi41: Add basic PM runtime support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Markus Schneider-Pargmann (TI) <msp@xxxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/dma/ti/cppi41.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/ti/cppi41.c b/drivers/dma/ti/cppi41.c
> index 458d20b12462..f5a824418fe7 100644
> --- a/drivers/dma/ti/cppi41.c
> +++ b/drivers/dma/ti/cppi41.c
> @@ -146,6 +146,9 @@ struct cppi41_dd {
>         struct list_head pending;       /* Pending queued transfers */
>         spinlock_t lock;                /* Lock for pending list */
>
> +       /* Register context may have been lost during system suspend */
> +       bool ctx_lost;
> +
>         bool is_suspended;
>  };
>
> @@ -1171,7 +1174,10 @@ static int __maybe_unused cppi41_suspend(struct device *dev)
>  {
>         struct cppi41_dd *cdd = dev_get_drvdata(dev);
>
> -       disable_sched(cdd);
> +       if (!pm_runtime_status_suspended(dev))
> +               disable_sched(cdd);
> +
> +       cdd->ctx_lost = true;
>
>         return 0;
>  }
> @@ -1182,6 +1188,9 @@ static int __maybe_unused cppi41_resume(struct device *dev)
>         struct cppi41_channel *c;
>         int i;
>
> +       if (pm_runtime_status_suspended(dev))
> +               return 0;
> +
>         for (i = 0; i < DESCS_AREAS; i++)
>                 cppi_writel(cdd->descs_phys, cdd->qmgr_mem + QMGR_MEMBASE(i));
>
> @@ -1196,6 +1205,8 @@ static int __maybe_unused cppi41_resume(struct device *dev)
>         cppi_writel(QMGR_SCRATCH_SIZE, cdd->qmgr_mem + QMGR_LRAM_SIZE);
>         cppi_writel(0, cdd->qmgr_mem + QMGR_LRAM1_BASE);
>
> +       cdd->ctx_lost = false;
> +
>         return 0;
>  }
>
> @@ -1217,6 +1228,9 @@ static int __maybe_unused cppi41_runtime_resume(struct device *dev)
>         struct cppi41_dd *cdd = dev_get_drvdata(dev);
>         unsigned long flags;
>
> +       if (cdd->ctx_lost)
> +               cppi41_resume(dev);
> +
>         spin_lock_irqsave(&cdd->lock, flags);
>         cdd->is_suspended = false;
>         cppi41_run_queue(cdd);
>
> --
> 2.55.0
>