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

[Tony Lindgren <tony@atomide.com>]

* 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. This can potentially leading
to pm_runtime_get() called multiple times?

So I think we'd also need cppi41_dma_cleanup_slave_sg()
or similar, and require they get called in a paired manner.

It might be better to add seprate PM runtime specific
functions that dma consumers can optionally call.

Regards,

Tony