This is a note to let you know that I've just added the patch titled
regmap: spi: Fix potential off-by-one when calculating reserved size
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
regmap-spi-fix-potential-off-by-one-when-calculating.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 2355b64dd1be6ff91b809fc882e9cb5026ce111e
Author: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Date: Wed Jun 5 23:53:15 2024 +0300
regmap: spi: Fix potential off-by-one when calculating reserved size
[ Upstream commit d4ea1d504d2701ba04412f98dc00d45a104c52ab ]
If we ever meet a hardware that uses weird register bits and padding,
we may end up in off-by-one error since x/8 + y/8 might not be equal
to (x + y)/8 in some cases.
bits pad x/8+y/8 (x+y)/8
4..7 0..3 0 0 // x + y from 4 up to 7
4..7 4..7 0 1 // x + y from 8 up to 11
4..7 8..11 1 1 // x + y from 12 up to 15
8..15 0..7 1 1 // x + y from 8 up to 15
8..15 8..15 2 2 // x + y from 16 up to 23
Fix this by using (x+y)/8.
Signed-off-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Link: https://msgid.link/r/20240605205315.19132-1-andy.shevchenko@xxxxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/base/regmap/regmap-spi.c b/drivers/base/regmap/regmap-spi.c
index 37ab23a9d034..7f14c5ed1e22 100644
--- a/drivers/base/regmap/regmap-spi.c
+++ b/drivers/base/regmap/regmap-spi.c
@@ -122,8 +122,7 @@ static const struct regmap_bus *regmap_get_spi_bus(struct spi_device *spi,
return ERR_PTR(-ENOMEM);
max_msg_size = spi_max_message_size(spi);
- reg_reserve_size = config->reg_bits / BITS_PER_BYTE
- + config->pad_bits / BITS_PER_BYTE;
+ reg_reserve_size = (config->reg_bits + config->pad_bits) / BITS_PER_BYTE;
if (max_size + reg_reserve_size > max_msg_size)
max_size -= reg_reserve_size;
