[PATCH v1 2/2] spi: stm32: split large transfers based on word size instead of bytes

[Leonard Göhrs]

The TSIZE register in CR2, to which the number of words to transfer
is written, is only 16 Bit. This limits transfers to 65535 SPI
_words_ at a time. The existing code uses spi_split_transfers_maxsize
to limit transfers to 65535 _bytes_ at a time.

This breaks large transfers with bits_per_word > 8, as they are
split inside of a word boundary by the odd size limit.

Split transfers based on the number of words instead.
This has the added benefit of not artificially limiting the maximum
length of bpw > 8 transfers to half or a quarter of the actual limit.

The combination of very large transfers and bits_per_word = 16 is triggered
e.g. by MIPI DBI displays when updating large parts of the screen.

Signed-off-by: Leonard Göhrs <l.goehrs at pengutronix.de>
---
 drivers/spi/spi-stm32.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index def09cf0dc14..d2e16f16fae6 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -984,9 +984,9 @@ static int stm32_spi_prepare_msg(struct spi_master *master,
 	if (spi->cfg->set_number_of_data) {
 		int ret;
 
-		ret = spi_split_transfers_maxsize(master, msg,
-						  STM32H7_SPI_TSIZE_MAX,
-						  GFP_KERNEL | GFP_DMA);
+		ret = spi_split_transfers_maxwords(master, msg,
+						   STM32H7_SPI_TSIZE_MAX,
+						   GFP_KERNEL | GFP_DMA);
 		if (ret)
 			return ret;
 	}
-- 
2.30.2