linux-kernel - Re: [PATCH v2 2/2] spi: spi-ti-qspi: Use bounce buffer if read buffer is not DMA'ble

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Date:   Tue, 25 Apr 2017 17:48:53 +0530
From:   Vignesh R <vigneshr@...com>
To:     Mark Brown <broonie@...nel.org>
CC:     <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] spi: spi-ti-qspi: Use bounce buffer if read buffer
 is not DMA'ble



On Friday 21 April 2017 10:36 PM, Mark Brown wrote:
> On Tue, Apr 11, 2017 at 05:22:25PM +0530, Vignesh R wrote:
>> Flash filesystems like JFFS2, UBIFS and MTD block layer can provide
>> vmalloc'd or kmap'd buffers that cannot be mapped using dma_map_sg() and
>> can potentially be in memory region above 32bit addressable region(ie
>> buffers belonging to memory region backed by LPAE) of DMA, implement
>> spi_flash_can_dma() interface to inform SPI core not to map such
>> buffers.
> 
> I'll apply this since it fixes bugs for your systems but it feels like
> something that we should be moving further into the core since LPAE
> isn't specific to your devices.  We should ideally have something
> (possibly in the DMA mapping code even) which does the remapping without
> the driver needing to know about it.
> 

I agree, there is a need to have generic remapping code. Also, I guess,
once UBIFS is moved to use kmalloc'd buffers SPI flash devices will not
have to worry much about vmalloc'd buffers.

-- 
Regards
Vignesh