linux-kernel - Re: [PATCH] dmaengine: edma: Reject slave configs using a buswidth of 8 and larger

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Message-ID: <13ff5f5c-3872-4af5-1baf-205fe01bb0f2@ti.com>
Date:   Thu, 21 Sep 2017 21:29:27 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vinod Koul <vinod.koul@...el.com>,
        Stefan Brüns <stefan.bruens@...h-aachen.de>
CC:     <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] dmaengine: edma: Reject slave configs using a buswidth of
 8 and larger




Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

On 2017-09-21 20:17, Vinod Koul wrote:
> On Sun, Sep 17, 2017 at 04:25:10PM +0200, Stefan Brüns wrote:
>> The driver would happily accept buswidth of 16/32/64 bytes and program
>> garbage to its registers.
> 
> Peter?

Well, eDMA as such has no limitation on the buswidth, the addr_width
become ACNT, counter for the inner loop - which we use to represent the
word length. In theory we could support 32K-1 long word with eDMA, which
we actually do in case of memcpy.

But the driver does state that it supports bus width of 1, 2, 3 and 4 bytes.

These are form the past and I never felt the need to check them.

I think it is fine to reject salve config when asking for longer dev
width. I might revisit later if the need comes..

Acked-by: Peter Ujfalusi <peter.ujfalusi@...com>

> 
>>
>> Signed-off-by: Stefan Brüns <stefan.bruens@...h-aachen.de>
>> ---
>>  drivers/dma/edma.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
>> index 3879f80a4815..c944ea339425 100644
>> --- a/drivers/dma/edma.c
>> +++ b/drivers/dma/edma.c
>> @@ -887,8 +887,8 @@ static int edma_slave_config(struct dma_chan *chan,
>>  {
>>  	struct edma_chan *echan = to_edma_chan(chan);
>>  
>> -	if (cfg->src_addr_width == DMA_SLAVE_BUSWIDTH_8_BYTES ||
>> -	    cfg->dst_addr_width == DMA_SLAVE_BUSWIDTH_8_BYTES)
>> +	if (cfg->src_addr_width >= DMA_SLAVE_BUSWIDTH_8_BYTES ||
>> +	    cfg->dst_addr_width >= DMA_SLAVE_BUSWIDTH_8_BYTES)
>>  		return -EINVAL;
>>  
>>  	memcpy(&echan->cfg, cfg, sizeof(echan->cfg));
>> -- 
>> 2.14.1
>>
> 

- Péter