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

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Message-ID: <5347AE49.5020109@ti.com>
Date:	Fri, 11 Apr 2014 14:26:41 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Peter Ujfalusi <peter.ujfalusi@...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 Friday 11 April 2014 02:20 PM, Peter Ujfalusi wrote:
> 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.

Sounds much better. I had posted some ideas about adding support for
channel priority in the core code but we can leave that for Vinod and
Dan to say if they really see a need for that.

Thanks,
Sekhar
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