* Peter Ujfalusi <peter.ujfalusi@xxxxxx> [191023 17:04]:
> On 10/23/19 6:31 PM, Tony Lindgren wrote:
> > diff --git a/drivers/dma/ti/cppi41.c b/drivers/dma/ti/cppi41.c
> > --- a/drivers/dma/ti/cppi41.c
> > +++ b/drivers/dma/ti/cppi41.c
> > @@ -586,9 +586,22 @@ static struct dma_async_tx_descriptor *cppi41_dma_prep_slave_sg(
> > enum dma_transfer_direction dir, unsigned long tx_flags, void *context)
> > {
> > struct cppi41_channel *c = to_cpp41_chan(chan);
> > + struct dma_async_tx_descriptor *txd = NULL;
> > + struct cppi41_dd *cdd = c->cdd;
> > struct cppi41_desc *d;
> > struct scatterlist *sg;
> > unsigned int i;
> > + int error;
> > +
> > + error = pm_runtime_get(cdd->ddev.dev);
>
> If pm_runtime_get()
> pm_runtime_mark_last_busy()+pm_runtime_put_autosuspend() around a code
> which updates a descriptor in _memory_ helps then this best described as
> works by luck ;)
It also checks the cpp41 state for cdd->is_suspended
though. AFAIK we do not currently have any other place
to tell the driver a DMA request is about to start at
some point soon.
> I have a feeling that if you put enough delay between prepare_sg and
> issue_pending in the usb driver then it will keep failing, no?
Nope, it will just queue it and run the queue when awake.
> fwiw, in the cppi41_dma_issue_pending() the driver does:
>
> error = pm_runtime_get(cdd->ddev.dev);
> ...
> if (!cdd->is_suspended)
> cppi41_run_queue(cdd);
> ...
> pm_runtime_mark_last_busy(cdd->ddev.dev);
> pm_runtime_put_autosuspend(cdd->ddev.dev);
>
> Without waiting for the transfer to complete?
The queue gets run when cpp41 is awake, runtime PM
reference is not released until completed.
> If issue_pending is not starting the transfer right away then the whole
> pm handling is broken in there. imho.
AFAIK there is no other way to do this without tagging
devices with pm_runtime_irq_safe(), which is nasty as
it takes a permanent use count on the parent device.
But yeah, some dmaengine API that can sleep to tell
a request is about to come would simplify things.
I don't think we have anything like that available
right now?
Regards,
Tony
