linux-kernel - Re: [PATCH v2 05/14] arm: common: edma: Select event queue 1 as default when booted with DT

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Date:	Fri, 11 Apr 2014 11:50:38 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Sekhar Nori <nsekhar@...com>, <dan.j.williams@...el.com>,
	<vinod.koul@...el.com>
CC:	<dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<joelf@...com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>,
	<davinci-linux-open-source@...ux.davincidsp.com>,
	<mporter@...aro.org>
Subject: Re: [PATCH v2 05/14] arm: common: edma: Select event queue 1 as default
 when booted with DT

On 04/11/2014 11:17 AM, Sekhar Nori wrote:
> On Tuesday 01 April 2014 06:36 PM, Peter Ujfalusi wrote:
>> Use the EVENTQ_1 for default and leave the EVENTQ_0 to be used by high
>> priority channels, like audio.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> 
> Acked-by: Sekhar Nori <nsekhar@...com>
> 
>> ---
>>  arch/arm/common/edma.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/common/edma.c b/arch/arm/common/edma.c
>> index 86a8b263278f..19520e2519d9 100644
>> --- a/arch/arm/common/edma.c
>> +++ b/arch/arm/common/edma.c
>> @@ -1546,7 +1546,8 @@ static int edma_of_parse_dt(struct device *dev,
>>  
>>  	pdata->queue_priority_mapping = queue_priority_map;
>>  
>> -	pdata->default_queue = 0;
>> +	/* select queue 1 as default */
> 
> It will be nice to expand the comment with explanation of why this is
> being chosen as default (lower priority queue by default for typical
> bulk data transfer).

Yes, extended comment is a good idea.

For the next version I think I'm going to change the code around default
TC/Queue and the non default queue selection, mostly based on Joel's comment:

EVENTQ_1 as default queue.
Set the EVENTQ_1 priority to 7
EVENTQ_0 priority is going to stay 0 and EVENTQ_2 as 2

Add new member to struct edma, like high_pri_queue.
When we set the queue priorities in edma_probe() we look for the highest
priority queue and save the number in high_pri_queue.

I will rename the edma_request_non_default_queue() to
edma_request_high_pri_queue() and it will assign the channel to the high
priority queue.

I think this way it is going to be more explicit and IMHO a bit more safer in
a sense the we are going to get high priority when we ask for it.

-- 
Péter
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