On Wed, May 09 2018, Boris Brezillon wrote: > On Fri, 27 Apr 2018 16:18:05 +1000 > NeilBrown <n...@brown.name> 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.
NeilBrown
>>
>> Thanks,
>> NeilBrown
>>
>> -----------------------8<------------------------
>>
>> m25p80 honours max_message_size and max_transfer_size
>> for reads, but not for writes.
>> I have a driver that has a max message size of 36 bytes
>> (command, address, 32 bytes data, all places in a FIFO
>> in the controller).
>> This requires m25p80_write() to honour the size limits.
>> For that to work, spi-nor needs to quietly accept partial
>> writes.
>>
>> With this, I can successfully re-flash my device.
>>
>> Signed-off-by: NeilBrown <n...@brown.name>
>> ---
>> drivers/mtd/devices/m25p80.c | 3 ++-
>> drivers/mtd/spi-nor/spi-nor.c | 7 -------
>> 2 files changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
>> index a4e18f6aaa33..7ded13507604 100644
>> --- a/drivers/mtd/devices/m25p80.c
>> +++ b/drivers/mtd/devices/m25p80.c
>> @@ -117,7 +117,8 @@ static ssize_t m25p80_write(struct spi_nor *nor, loff_t
>> to, size_t len,
>>
>> t[data_idx].tx_buf = buf;
>> t[data_idx].tx_nbits = data_nbits;
>> - t[data_idx].len = len;
>> + t[data_idx].len = min3(len, spi_max_transfer_size(spi),
>> + spi_max_message_size(spi) - cmd_sz);
>> spi_message_add_tail(&t[data_idx], &m);
>>
>> ret = spi_sync(spi, &m);
>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>> index 42ae9a1529bb..cfa15f2801ad 100644
>> --- a/drivers/mtd/spi-nor/spi-nor.c
>> +++ b/drivers/mtd/spi-nor/spi-nor.c
>> @@ -1445,13 +1445,6 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t
>> to, size_t len,
>> goto write_err;
>> *retlen += written;
>> i += written;
>> - if (written != page_remain) {
>> - dev_err(nor->dev,
>> - "While writing %zu bytes written %zd bytes\n",
>> - page_remain, written);
>> - ret = -EIO;
>> - goto write_err;
>> - }
>> }
>>
>> write_err:
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