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

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Date:	Mon, 29 Aug 2011 18:18:33 +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 Mon, 2011-08-29 at 14:21 +0200, Guennadi Liakhovetski wrote:
> On Mon, 29 Aug 2011, Vinod Koul wrote:
> 
> > 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.
> 
> Sorry, I thought, you wanted to avoid extra counting, because runtime-pm 
> counts by itself. Now you propose to count...
see below it doesn't count but iterate thru list
> 
> > 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);
> 
> Not all dma users have callbacks.
Do you have such usage today, at least I dont :)
Nevertheless, in tx_submit adding a simple flag in your drivers
descriptor structure can tell you whether to call _put() or not. Agreed?

--
~Vinod 
> 
> > 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.
> 
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/



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