Hi Vinod,


On Fri, Feb 6, 2015 at 1:41 AM, Vinod Koul [off-list ref] wrote:

On Thu, Feb 05, 2015 at 05:29:06PM +0530, Rameshwar Sahu wrote:

quoted

Hi Vinod,

Thanks for reviewing this patch.

Please see inline......

Please STOP top posting

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+}
+
+static void xgene_dma_issue_pending(struct dma_chan *channel)
+{
+     /* Nothing to do */
+}

What do you mean by nothing to do here
See Documentation/dmaengine/client.txt Section 4 & 5

This docs is only applicable on slave DMA operations, we don't support
slave DMA, it's only master.
Our hw engine is designed in the way that there is no scope of
flushing pending transaction explicitly by sw.
We have circular ring descriptor dedicated to engine. In submit
callback  we are queuing descriptor and informing to engine, so after
this it's internal to hw to execute descriptor one by one.

But the API expectations on this are _same_

No the API expects you to maintain a SW queue, then push to your ring buffer
when you get issue_pending. Issue pending is the start of data transfer, you
client will expect accordingly.

Okay, I will maintain a sw queue, and will push sw descriptor to hw in
this callback.

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+     /* Run until we are out of length */
+     do {
+             /* Create the largest transaction possible */
+             copy = min_t(size_t, len, DMA_MAX_64BDSC_BYTE_CNT);
+
+             /* Prepare DMA descriptor */
+             xgene_dma_prep_cpy_desc(chan, slot, dst, src, copy);
+

This is wrong. The descriptor is supposed to be already prepared and now it
has to be submitted to queue

Due to the race in tx_submit call from the client, need to serialize
the submission of H/W DMA descriptors.
 So we are making  shadow copy in prepare DMA  routine and  preparing
actual descriptor during tx_submit call.

Thats an abuse of API and I dont see a reason why this race should happen in
the first place.

So you get a prep call, you prepare a desc in SW. Then submit pushes it to a
queue. Finally in issue pending you push them to HW. Simple..?

I agree, I will do it and post another version soon.

--
~Vinod
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