linux-kernel - Re: [PATCH v2 2/2] dmaengine: Add DW AXI DMAC driver

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Date:   Thu, 27 Apr 2017 13:21:41 +0000
From:   Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
To:     "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>
CC:     "vinod.koul@...el.com" <vinod.koul@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] dmaengine: Add DW AXI DMAC driver

On Wed, 2017-04-26 at 18:04 +0300, Andy Shevchenko wrote:
> On Tue, 2017-04-25 at 21:12 +0300, Andy Shevchenko wrote:
> > On Tue, 2017-04-25 at 15:16 +0000, Eugeniy Paltsev wrote:
> > > On Mon, 2017-04-24 at 19:56 +0300, Andy Shevchenko wrote:
> > > > On Mon, 2017-04-24 at 15:55 +0000, Eugeniy Paltsev wrote:
> > > > Descriptor is active until terminate_all() is called or new
> > > > descriptor
> > > > is supplied. So, the caller has a quite time to check on it.
> > > >
> > > > So, what's wrong on it by your opinion?
> > >
> > > Hmm, this looks OK. (In my example (hsu/hsu.c driver) error
> > > descriptors
> > > are not freed even after terminate_all is called)
> >
> > If it's active it will be freed.
> > Otherwise caller should check somewhere that descriptor fails.
> >
> > But actually this is fragile and we need to monitor failed
> > descriptors.
> > Thanks for reporting.
> >
> > >
> > > > Of course, if you want to keep by some reason (should be stated
> > > > what
> > > > the reason in comment) erred descriptors, you can do that.
> > >
> > > So, I'll create desc_error list and store failed descriptors in
> > > this
> > > list until terminate_all() is called.
> > > Is it OK implementation?
> >
> > Nope, we need to amend virt-chan API for that. I'm on it. Will send
> > a series soon.
>
> I have to correct what I wrote before.
>
> We have two options:
> a) one I proposed above;
> b) move descriptor to complete list and call complete callback with
> result.
>
> So, it looks like the b) variant is what is done already in 4 (did I
> calculate correctly?) drivers and respective users.

In my opinion we should call error descriptor complete callback.
But I don't think we should move error descriptor to desc_completed
list.

When descriptor following our error descriptor will be completed
successfully vchan tasklet will be called.
So all descriptors from desc_completed list will be freed (including
our error descriptor)
We'll lost information about error descriptors and we'll not be able to
return correct status from dma_async_is_tx_complete().

In my opinion, we should create desc_error list.
When we get error we'll move descriptor to desc_error list and call
complete callback.

--
 Eugeniy Paltsev