From: Andy Shevchenko Date: Wed, 5 Jun 2024 20:53:15 +0000 (+0300) Subject: regmap: spi: Fix potential off-by-one when calculating reserved size X-Git-Tag: v6.11-rc1~205^2~30 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d4ea1d504d2701ba04412f98dc00d45a104c52ab;p=thirdparty%2Fkernel%2Flinux.git regmap: spi: Fix potential off-by-one when calculating reserved size 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 Link: https://msgid.link/r/20240605205315.19132-1-andy.shevchenko@gmail.com Signed-off-by: Mark Brown --- diff --git a/drivers/base/regmap/regmap-spi.c b/drivers/base/regmap/regmap-spi.c index 094cf2a2ca3cd..14b1d88997cbe 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;