Messages in this thread | | | Subject | Re: [PATCH] dma: shdma: transfer based runtime PM | From | "Koul, Vinod" <> | Date | Thu, 25 Aug 2011 22:50:50 +0530 |
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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)
Let me know if there is a case for you which doesn't fit in above
-- ~Vinod
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