Messages in this thread | | | From | NeilBrown <> | Date | Thu, 10 May 2018 08:28:25 +1000 | Subject | Re: [PATCH/RFC] mtd: spi-nor: honour max_message_size for spi-nor writes. |
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On Wed, May 09 2018, Boris Brezillon wrote:
> On Fri, 27 Apr 2018 16:18:05 +1000 > NeilBrown <neil@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 <neil@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: [unhandled content-type:application/pgp-signature] | |