Subject: [PATCH] dmaengine: pl330: Set residue in tx_status callback

From: [email-masked] (Vinod Koul)
Date: Fri, 5 Dec 2014 20:45:16 +0530

On Wed, Dec 03, 2014 at 01:21:37PM +0530, Jassi Brar wrote:
> On 3 December 2014 at 10:17, Padma Venkat <[email-masked]> wrote:
> > Hi Lars,
> >
> > [snip]
> >>>> +
> >>>> +   ret = dma_cookie_status(chan, cookie, txstate);
> >>>> +   if (ret == DMA_COMPLETE || !txstate)
> >>>> +           return ret;
> >>>> +
> >>>> +   used = txstate->used;
> >>>> +
> >>>> +   spin_lock_irqsave(&pch->lock, flags);
> >>>> +   sar = readl(regs + SA(thrd->id));
> >>>> +   dar = readl(regs + DA(thrd->id));
> >>>> +
> >>>> +   list_for_each_entry(desc, &pch->work_list, node) {
> >>>> +           if (desc->status == BUSY) {
> >>>> +                   current_c = desc->txd.cookie;
> >>>> +                   if (first) {
> >>>> +                           first_c = desc->txd.cookie;
> >>>> +                           first = false;
> >>>> +                   }
> >>>> +
> >>>> +                   if (first_c < current_c)
> >>>> +                           residue += desc->px.bytes;
> >>>> +                   else {
> >>>> +                           if (desc->rqcfg.src_inc && pl330_src_addr_in_desc(desc, sar)) {
> >>>> +                                   residue += desc->px.bytes;
> >>>> +                                   residue -= sar - desc->px.src_addr;
> >>>> +                           } else if (desc->rqcfg.dst_inc && pl330_dst_addr_in_desc(desc, dar))
> >>>> {
> >>>> +                                   residue += desc->px.bytes;
> >>>> +                                   residue -= dar - desc->px.dst_addr;
> >>>> +                           }
> >>>> +                   }
> >>>> +           } else if (desc->status == PREP)
> >>>> +                   residue += desc->px.bytes;
> >>>> +
> >>>> +           if (desc->txd.cookie == used)
> >>>> +                   break;
> >>>> +   }
> >>>> +   spin_unlock_irqrestore(&pch->lock, flags);
> >>>> +   dma_set_residue(txstate, residue);
> >>>> +   return ret;
> >>>>   }
> > [snip]
> >>>
> >>> Any comment on this patch?
> >>
> >> Well it doesn't break audio, but I don't think it has the correct haviour
> >> for all cases yet.
> >
> > OK. Any way of testing other cases like scatter-gather and memcopy.  I
> > verified memcopy in dmatest but it seems not doing anything with
> > residue bytes.
> >
> >>
> >> Again, the semantics are that it should return the progress of the transfer
> >>
> >> for which the allocation function returned the cookie that is passe to this
> >
> > May be my understanding is wrong. For clarification..In the
> > snd_dmaengine_pcm_pointer it is subtracting the residue bytes from the
> > total buffer bytes not from period bytes. So how it expects
> > the progress of the transfer of the passed cookie which just holds period bytes?
> >
> >>
> >> function. You have to consider that there might be multiple different
> >> descriptors submitted and in the work list, not just the one we want to know
> >
> > Even though there are multiple descriptors in the work list, at a time
> > only two descriptors are in busy state(as per the documentation in the
> > driver) and all the descriptors cookie number is in incremental order.
> > Not sure for other cases how it will be.
> >
> Yes.
> 
> Tracing the history ... I think we could have done without
> 
> 04abf5daf7d  dma: pl330: Differentiate between submitted and issued descriptors
> 
>     The pl330 dmaengine driver currently does not differentiate
> between submitted
>     and issued descriptors. It won't start transferring a newly submitted
>     descriptor until issue_pending() is called, but only if it is idle. If it is
>     active and a new descriptor is submitted before it goes idle it will happily
>     start the newly submitted descriptor once all earlier submitted
> descriptors have
>     been completed. This is not a 100% correct with regards to the dmaengine
>     interface semantics. A descriptor is not supposed to be started
> until the next
>     issue_pending() call after the descriptor has been submitted.
> 
> 
> because the reasoning above seems incorrect considering the following
> documentation...
> 
> Documentation/crypto/async-tx-api.txt says
>   " .... Once a driver-specific threshold is met the driver
> automatically issues pending operations.  An application can force this
> event by calling async_tx_issue_pending_all(). ...."
> 
> And
> 
> include/linux/dmaengine.h says
>   dma_async_tx_descriptor.tx_submit(): set the prepared descriptor(s)
> to be executed by the engine
"to be" here can lead to different conculsion. I will reword this :)

@tx_submit: accept the descriptor and assign ordered cookie and mark the
descriptor pending. To be pushed on .issue_pending() call

-- 
~Vinod
> 
> so theoretically a driver, not starting transfer until
> issue_pending(), is "broken".
> At best the patch at 04abf5daf7d makes the driver slightly more
> complicated and the reason behind confusion such as in this thread.
> 
> -jassi

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