linux-kernel - Re: [PATCH] dma: shdma: transfer based runtime PM

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Date:	Mon, 29 Aug 2011 17:41:49 +0530
From:	Vinod Koul <vinod.koul@...ux.intel.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH] dma: shdma: transfer based runtime PM

On Fri, 2011-08-26 at 01:11 +0200, Guennadi Liakhovetski wrote:
> On Thu, 25 Aug 2011, Koul, Vinod wrote:
> > Wont it be easy to to do:
> > - pm_runtime_get() in each submit
> > - pm_runtime_put() in each callback
> > Normal case above would work just fine
> > - In terminate case, count the number of issued transactions, and call
> > pm_runtime_put() for each canceled transaction
> > (i am assuming that for each timeout error, the client will call
> > terminate)
> 
> As I said, this won't be very easy to do this in a robust way. You'd have 
> to scan your list of DMA blocks and see, which of them belong to one 
> descriptor, and once you reach the end of that descriptor, issue a put(). 
> Perhaps, this can be done, but my choice went to the currently presented 
> solution.
If you count the number of descriptor submitted in your submitted list
and call _put for each, I see no reason why it wont be simple and better
than current approach.

Something like:
/* since callback is set for last descriptor of chain, we call runtime
 * put for that desc alone
 */
list_for_each_entry_safe(desc, __desc, sh_chan->ld_queue, node) {
	if (desc->async_tx.callback)
		pm_runtime_put(device);

If i read shdma correctly, descriptors are put into ld_queue of channel
and any pending should be checked in this list alone.
For normal case again you check for the callback to decide if you need
to call pm_runtime_put() or not.

--
~Vinod

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