linux-kernel - Re: [RFC PATCH 2/2] mtd: devices: m25p80: Enable spi-nor bounce buffer support

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Date:   Wed, 1 Mar 2017 10:24:18 +0530
From:   Vignesh R <vigneshr@...com>
To:     Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>,
        Frode Isaksen <fisaksen@...libre.com>,
        <linux-spi@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] mtd: devices: m25p80: Enable spi-nor bounce
 buffer support



On Wednesday 01 March 2017 03:11 AM, Richard Weinberger wrote:
> Vignesh,
> 
> Am 27.02.2017 um 13:08 schrieb Vignesh R:
>> Many SPI controller drivers use DMA to read/write from m25p80 compatible
>> flashes. Therefore enable bounce buffers support provided by spi-nor
>> framework to take care of handling vmalloc'd buffers which may not be
>> DMA'able.
>>
>> Signed-off-by: Vignesh R <vigneshr@...com>
>> ---
>>  drivers/mtd/devices/m25p80.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
>> index c4df3b1bded0..d05acf22eadf 100644
>> --- a/drivers/mtd/devices/m25p80.c
>> +++ b/drivers/mtd/devices/m25p80.c
>> @@ -241,6 +241,7 @@ static int m25p_probe(struct spi_device *spi)
>>  	else
>>  		flash_name = spi->modalias;
>>  
>> +	nor->flags |= SNOR_F_USE_BOUNCE_BUFFER;
> 
> Isn't there a better way to detect whether a bounce buffer is needed or not?

Yes, I can poke the spi->master struct to see of dma channels are
populated and request SNOR_F_USE_BOUNCE_BUFFER accordingly:

-       nor->flags |= SNOR_F_USE_BOUNCE_BUFFER;
+       if (spi->master->dma_tx || spi->master->dma_rx)
+               nor->flags |= SNOR_F_USE_BOUNCE_BUFFER;
+

-- 
Regards
Vignesh