[PATCH/RFC] mtd: spi-nor: honour max_message_size for spi-nor writes.

From: NeilBrown
Date: Fri Apr 27 2018 - 02:18:23 EST

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:

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?



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

With this, I can successfully re-flash my device.

Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
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;
- }


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