linux-kernel - Re: [PATCH v3 6/7] dmaengine: omap-dma: Remove mapping between virtual channels and requests

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Date:	Tue, 31 Mar 2015 18:44:30 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<vinod.koul@...el.com>, <tony@...mide.com>,
	<grant.likely@...aro.org>, <dmaengine@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <robh+dt@...nel.org>,
	<nm@...com>
Subject: Re: [PATCH v3 6/7] dmaengine: omap-dma: Remove mapping between virtual
 channels and requests

On 03/27/2015 10:22 PM, Russell King - ARM Linux wrote:
> On Fri, Mar 27, 2015 at 02:26:52PM +0200, Peter Ujfalusi wrote:
>> Do not direct map the virtual channels to sDMA request number. When the
>> sDMA is behind of a crossbar this direct mapping can cause situations when
>> certain channel can not be requested since the crossbar request number
>> will no longer match with the sDMA request line.
>> The direct mapping for virtual channels with HW request lines will make it
>> harder to implement MEM_TO_MEM mode for the driver.
> 
> There's no point having 127 virtual DMA channels then... is there?
> We might as well reduce the number down to a more reasonable set
> rather than wasting memory.

I was also come to the same conclusion. My plan was to change the virtual DMA
channels to the same as the sDMA's logical channels.

>> @@ -1049,7 +1050,6 @@ static int omap_dma_chan_init(struct omap_dmadev *od, int dma_sig)
>>  		return -ENOMEM;
>>  
>>  	c->reg_map = od->reg_map;
>> -	c->dma_sig = dma_sig;
> 
> That's the only user of dma_sig in this function.  Why not remove it from
> the function prototype and its caller?
> 


-- 
Péter
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