Re: [PATCH] dmaengine: cppi41: Fix cppi41_dma_prep_slave_sg() when idle

[Tony Lindgren <tony@atomide.com>]

* Grygorii Strashko <grygorii.strashko@ti.com> [191023 21:43]:
> 
> 
> On 24/10/2019 00:27, Tony Lindgren wrote:
> > * Grygorii Strashko <grygorii.strashko@ti.com> [191023 20:56]:
> > > On 23/10/2019 23:18, Tony Lindgren wrote:
> > > > And no, adding pm_runtime_get_sync() to issue_pending is not
> > > > a solution. There may be clocks and regulators that need to
> > > > be powered up, and we don't want to use pm_runtime_irq_safe()
> > > > because of the permanent use count on the parent.
> > > 
> > > 5 cents.
> > > 
> > > I think the right thing might be to get rid of pm_runtime_xxx()
> > > in cppi41_dma_issue_pending(). So overall approach will be:
> > > 
> > > - new job -> cppi41_dma_prep_slave_sg() -> pm_runtime_get()
> > > - issue_pending: fill backlog if suspended or run_queue if active (pm_runtime_active())
> > > - job done: dmaengine_desc_get_callback_invoke() ->
> > > 
> > > 	dmaengine_desc_get_callback_invoke();
> > > 	pm_runtime_mark_last_busy(cdd->ddev.dev);
> > > 	pm_runtime_put_autosuspend(cdd->ddev.dev);
> > >    in all places.
> > > 
> > > It even might allow to get rid of cdd->lock.
> > 
> > Well I don't think cppi41_dma_prep_slave_sg() is necessarily
> > paired with anything currently.
> 
> It should - dma cmpletion callbacks have to be called somewhere.

Well what I meant is there's no guarantee that we have
cppi41_dma_issue_pending() followed by cppi41_dma_prep_slave_sg()
currently :)

>  This can potentially leading
> > to pm_runtime_get() called multiple times?
> 
> That's the idea - increase pm_counter as many times as jobs submitted.

Right, but that needs to be done in a paired manner so the
API is clear to everyone and does not lead into unpaired
PM runtime calls.

Regards,

Tony