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

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Date:   Wed, 26 Apr 2017 18:04:35 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.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>,
        "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 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.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy