[PATCH v7 5/5] spi: dw: Round of n_bytes to power of 2

Joy Chakraborty
2023-04-18T05:29:51Z

n_bytes variable in the driver represents the number of bytes per word
that needs to be sent/copied to fifo. Bits/word can be between 8 and 32
bits from the client but in memory they are a power of 2, same is mentioned
in spi.h header:
"
* @bits_per_word: Data transfers involve one or more words; word sizes
* like eight or 12 bits are common. In-memory wordsizes are
* powers of two bytes (e.g. 20 bit samples use 32 bits).
* This may be changed by the device's driver, or left at the
* default (0) indicating protocol words are eight bit bytes.
* The spi_transfer.bits_per_word can override this for each transfer.
"

Hence, round of n_bytes to a power of 2 to avoid values like 3 which
would generate unalligned/odd accesses to memory/fifo.

Fixes: a51acc2400d4 ("spi: dw: Add support for 32-bits max xfer size")
Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Joy Chakraborty <joychakr@google.com>
---
drivers/spi/spi-dw-core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
index c3bfb6c84cab..a6486db46c61 100644
--- a/drivers/spi/spi-dw-core.c
+++ b/drivers/spi/spi-dw-core.c
@@ -426,7 +426,7 @@ static int dw_spi_transfer_one(struct spi_controller *master,
int ret;

dws->dma_mapped = 0;
- dws->n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);
+ dws->n_bytes = roundup_pow_of_two(DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE));
dws->tx = (void *)transfer->tx_buf;
dws->tx_len = transfer->len / dws->n_bytes;
dws->rx = transfer->rx_buf;
--
2.40.0.634.g4ca3ef3211-goog