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    SubjectRe: [PATCH] dma: shdma: transfer based runtime PM
    Hi Vinod

    On Tue, 30 Aug 2011, Guennadi Liakhovetski wrote:

    > On Tue, 30 Aug 2011, Vinod Koul wrote:
    >
    > > On Tue, 2011-08-30 at 09:12 +0200, Guennadi Liakhovetski wrote:
    > > > On Mon, 29 Aug 2011, Vinod Koul wrote:
    > > > > > > 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?
    > > >
    > > > Yes, I agree, that one could make this work too. Still, I do not
    > > > understand how and why this is better to the extent, that I have to
    > > > reimplement my patch, retest and resubmit it. Maybe Dan or Paul have an
    > > > opinion on this?
    > > But wont it make code look simpler and cleaner, you don't reply on your
    > > counters but on pm_runtime infrastructure to do the job.
    >
    > Sorry, I see it differently. I don't use any counters in my patch. I'm
    > only checking for empty queue, i.e., I'm just identifying the first
    > descriptor submission and the last completion or termination.
    >
    > > You juts need
    > > to call _put/_get at right places, which IMO l;ooks lot simpler than
    > > current approach
    >
    > If we didn't have to check for exact symmetry, then yes, I agree, this
    > would be cleaner. I.e., if we indeed had well-defined entry- and
    > exit-points, which are guaranteed to be called exact same number of times.
    > Like, e.g., with file open() / close() etc. But since we don't have this
    > symmetry, and instead have to add flags and iterate lists, this doesn't
    > look natural and simple to me anymore, sorry.

    What about this one? Would you be prepared to take it as is, or you still
    think, that a pm_runtime_get*() on each descriptor submission would be
    better?

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


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