linux-kernel - Re: [PATCH] dmaengine: dw: fix cyclic transfers

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Date:	Mon, 11 Jan 2016 12:19:50 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Viresh Kumar <vireshk@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: dw: fix cyclic transfers

Viresh Kumar <viresh.kumar@...aro.org> writes:

> On 10-01-16, 20:54, Mans Rullgard wrote:
>> Commit 61e183f83069 ("dmaengine/dw_dmac: Reconfigure interrupt and
>> chan_cfg register on resume") moved some channel initialisation to
>> a new function which must be called before starting a transfer.
>> 
>> This adds the necessary dwc_initialize() call to dw_dma_cyclic_start()
>> which was missed in the original commit.
>> 
>> Fixes: 61e183f83069 ("dmaengine/dw_dmac: Reconfigure interrupt and chan_cfg register on resume")
>> Signed-off-by: Mans Rullgard <mans@...sr.com>
>> ---
>> Andy, do you want to collect this with your other patches?  It's trivial
>> enough that it can go in separately without conflicts too.
>> ---
>>  drivers/dma/dw/core.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
>> index 7067b6ddc1db..2917f75b67b4 100644
>> --- a/drivers/dma/dw/core.c
>> +++ b/drivers/dma/dw/core.c
>> @@ -1265,6 +1265,8 @@ int dw_dma_cyclic_start(struct dma_chan *chan)
>>  		return -EBUSY;
>>  	}
>>  
>> +	dwc_initialize(dwc);
>> +
>>  	dma_writel(dw, CLEAR.ERROR, dwc->mask);
>>  	dma_writel(dw, CLEAR.XFER, dwc->mask);
>
> Ahh, that's a very very old bug :(

It's not the only one, I'm afraid.

> Okay, things got cleaned up by putting the dwc_initialize() call
> within dwc_dostart() and so it worked for all other DMA APIs.
>
> What about calling dwc_dostart() from within dw_dma_cyclic_start()?
> That will simplify it and remove code duplication issue as well.

Good idea.  New patch coming up.

-- 
Måns Rullgård