linux-kernel - Re: [PATCH AUTOSEL for 4.9 44/56] ASoC: dwc: Fix PIO mode initialization

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Date:   Wed, 15 Nov 2017 12:46:37 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Mark Brown <broonie@...nel.org>, <alexander.levin@...izon.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL for 4.9 44/56] ASoC: dwc: Fix PIO mode
 initialization

Hi Mark,

On 15-11-2017 10:54, Mark Brown wrote:
> On Wed, Nov 15, 2017 at 02:45:45AM +0000, alexander.levin@...izon.com wrote:
>
>> We can no longer rely on the return value of
>> devm_snd_dmaengine_pcm_register(...) to check if the DMA
>> handle is declared in the DT.
>> Previously this check activated PIO mode but currently
>> dma_request_chan returns either a valid channel or -EPROBE_DEFER.
> So when did the corresponding change to the dmaengine API go in?

Looks like this was introduced in a8135d0d79e9 ("dmaengine: core:
Introduce new, universal API to request a channel") but looking
at soc-generic-dmaengine-pcm.c I see that this would never work
anyway because dmaengine_pcm_request_chan_of() also returns
either zero or -EPROBE_DEFER.

>
>> In order to activate PIO mode check instead if the interrupt
>> line is declared. This reflects better what is documented in
>> the DT bindings (see Documentation/devicetree/bindings/sound/
>> designware-i2s.txt).
>> Also, initialize use_pio variable which was never being set
>> causing PIO mode to never work.
> Though if PIO mode never worked presumably this isn't that urgent...

Yeah, and we also have this. Its my fault, I was using a
different tree for testing at the time. But if we could backport
this it would be nice because we and our clients use this PIO
driver in ARC AXS101 Development Platform. (A side note is that
the DT bindings were only recently introduced but I think its
more easier to add the bindings instead of fixing this driver ...).

Best Regards,
Jose Miguel Abreu