Re: [PATCH] dmaengine: qcom: bam_dma: fix runtime PM underflow

[Caleb Connolly <caleb.connolly@xxxxxxxxxx>]

On 16/06/2022 15:00, Vinod Koul wrote:
> On 09-06-22, 20:50, Caleb Connolly wrote:
> > When PM runtime is disabled, pm_runtime_get() isn't called, but
> > pm_runtime_put() still is. Fix this by creating a matching wrapper
> > on pm_runtime_put_autosuspend().
> >
> > Fixes: dbad41e7bb5f ("dmaengine: qcom: bam_dma: check if the runtime pm enabled")
> > Signed-off-by: Caleb Connolly <caleb.connolly@xxxxxxxxxx>
> > ---
> >   drivers/dma/qcom/bam_dma.c | 18 +++++++++++++-----
> >   1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> > index 87f6ca1541cf..a36dedee262e 100644
> > --- a/drivers/dma/qcom/bam_dma.c
> > +++ b/drivers/dma/qcom/bam_dma.c
> > @@ -566,6 +566,14 @@ static int bam_pm_runtime_get_sync(struct device *dev)
> >   	return 0;
> >   }
> >   
> > +static int bam_pm_runtime_put_autosuspend(struct device *dev)
> > +{
> > +	if (pm_runtime_enabled(dev))
> > +		return pm_runtime_put_autosuspend(dev);
> > +
> > +	return 0;
> > +}
>
> should we really do a wrapper to fix this ;-) I would think dropping the
> get wrapper and calling pm_runtime_get() unconditionally would be
> better..?
The original pm_runtime_get() wrapper was added because _get() returns -EACCES 
if PM is disabled for the device, I've read through some of the pm_runtime docs 
and I don't see any way to handle this nicely in the framework. I think the real 
fix will have to be in pm_runtime.

I can rework this to explicitly check for -EACCES on every _get() call, but we 
still need to check if pm_runtime is enabled before calling _put().
> > +
> >   /**
> >    * bam_free_chan - Frees dma resources associated with specific channel
> >    * @chan: specified channel
> > @@ -617,7 +625,7 @@ static void bam_free_chan(struct dma_chan *chan)
> >   
> >   err:
> >   	pm_runtime_mark_last_busy(bdev->dev);
> > -	pm_runtime_put_autosuspend(bdev->dev);
> > +	bam_pm_runtime_put_autosuspend(bdev->dev);
> >   }
> >   
> >   /**
> > @@ -793,7 +801,7 @@ static int bam_pause(struct dma_chan *chan)
> >   	bchan->paused = 1;
> >   	spin_unlock_irqrestore(&bchan->vc.lock, flag);
> >   	pm_runtime_mark_last_busy(bdev->dev);
> > -	pm_runtime_put_autosuspend(bdev->dev);
> > +	bam_pm_runtime_put_autosuspend(bdev->dev);
> >   
> >   	return 0;
> >   }
> > @@ -819,7 +827,7 @@ static int bam_resume(struct dma_chan *chan)
> >   	bchan->paused = 0;
> >   	spin_unlock_irqrestore(&bchan->vc.lock, flag);
> >   	pm_runtime_mark_last_busy(bdev->dev);
> > -	pm_runtime_put_autosuspend(bdev->dev);
> > +	bam_pm_runtime_put_autosuspend(bdev->dev);
> >   
> >   	return 0;
> >   }
> > @@ -936,7 +944,7 @@ static irqreturn_t bam_dma_irq(int irq, void *data)
> >   	}
> >   
> >   	pm_runtime_mark_last_busy(bdev->dev);
> > -	pm_runtime_put_autosuspend(bdev->dev);
> > +	bam_pm_runtime_put_autosuspend(bdev->dev);
> >   
> >   	return IRQ_HANDLED;
> >   }
> > @@ -1111,7 +1119,7 @@ static void bam_start_dma(struct bam_chan *bchan)
> >   			bam_addr(bdev, bchan->id, BAM_P_EVNT_REG));
> >   
> >   	pm_runtime_mark_last_busy(bdev->dev);
> > -	pm_runtime_put_autosuspend(bdev->dev);
> > +	bam_pm_runtime_put_autosuspend(bdev->dev);
> >   }
> >   
> >   /**
> > --
> > 2.36.1

--
Kind Regards,
Caleb (they/he)