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Message-ID: <Pine.LNX.4.64.1108260107550.17190@axis700.grange> Date: Fri, 26 Aug 2011 01:11:14 +0200 (CEST) From: Guennadi Liakhovetski <g.liakhovetski@....de> To: "Koul, Vinod" <vinod.koul@...el.com> 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 Thu, 25 Aug 2011, Koul, Vinod wrote: > On Thu, 2011-08-25 at 16:55 +0200, Guennadi Liakhovetski wrote: > > On Thu, 25 Aug 2011, Koul, Vinod wrote: > > > > > On Thu, 2011-08-25 at 16:37 +0200, Guennadi Liakhovetski wrote: > > > > On Thu, 25 Aug 2011, Koul, Vinod wrote: > > > > > > > > > On Thu, 2011-08-18 at 16:55 +0200, Guennadi Liakhovetski wrote: > > > > > > Currently the shdma dmaengine driver uses runtime PM to save power, when > > > > > > no channel on the specific controller is requested by a user. This patch > > > > > > switches the driver to count individual DMA transfers. That way the > > > > > > controller can be powered down between transfers, even if some of its > > > > > > channels are in use. > > > > > No, I don't agree with the approach here, you don't need to count the > > > > > transfers, the runtime_pm framework does that very well for you. > > > > > > > > > > What you need to do is to call pm_runtime_get() in your .issue_pending > > > > > callback (NOT in tx_submit anyway, this needs to be fixed in driver, see > > > > > the Documentation/dmaengine.txt > > > > > And once the transfer has completed you need to call pm_rumtime_put() > > > > > > > > This has been discussed before: > > > > > > > > http://marc.info/?l=linux-sh&m=131004613801231&w=2 > > > uh, yes but at least the runtime_xxx needs to get fixed. > > > > This isn't so easy either. In principle, yes, I know, that pm_runtime_* > > calls count depth. But I don't think the DMA case is simple enough for > > that. It's not necessarily one in - one out. Think about terminating > > transfers, timing out, closing the channel, etc. In those cases you'd have > > to count pending transfers and pm_runtime_put() for each of them. This is > > even less trivial on shdma, where DMA transfers get split into sg-lists, > > which are then all queued on a single queue. So, you'd have to scan that > > queue and check for transfer borders... That's why I decided that doing > > just one get() on the first descriptor and one put() on the last one would > > be easier and more robust. > 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. Thanks Guennadi > Let me know if there is a case for you which doesn't fit in above > > -- > ~Vinod --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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