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SubjectRe: [PATCH/RFC] mtd: spi-nor: honour max_message_size for spi-nor writes.
On 05/10/2018 12:28 AM, NeilBrown wrote:
> On Wed, May 09 2018, Boris Brezillon wrote:
>> On Fri, 27 Apr 2018 16:18:05 +1000
>> NeilBrown <> wrote:
>>> Hi,
>>> I've labeled this an RFC because I'm really not sure about removing the
>>> error path from spi_nor_write() -- maybe that really matters. But on
>>> my hardware, performing multiple small spi writes to the flash seems
>>> to work.
>>> The spi driver is drivers/staging/mt7621-spi. Possibly this needs to
>>> use DMA instead of a FIFO (assuming the hardware can) - or maybe
>>> drivers/spi/spi-mt65xx.c can be made to work on this hardware, though
>>> that is for an ARM SOC and mt7621 is a MIPS SOC.
>>> I note that openwrt has similar patches:
>>> target/linux/generic/pending-4.14/450-mtd-spi-nor-allow-NOR-driver-to-write-fewer-bytes-th.patch
>>> They also change the spi driver to do a short write, rather
>>> than change m25p80 to request a short write.
>>> Is there something horribly wrong with this?
>> Marek, any opinion on this patch?
> Hi,
> thanks for following up.
> I have since found that I don't need this patch, though maybe others
> still do(??).
> My hardware can only send 36 bytes and receive 32 in a single
> transaction. However I can run a sequence of transactions
> to process a whole message no matter how large that message is. As
> long as I keep chip-select asserted, all the slave device sees is that
> the clock period isn't quite constant, and the slave shouldn't care
> much about that.
> When reading from flash, I found that handling large messages with
> multiple hardware transactions was 50% faster than breaking the
> read down into lots of 32 byte messages.
> So, I won't object if this patch is forgotten. Thanks for
> your time anyway.

Nice, which hardware is that ?

Best regards,
Marek Vasut

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