spi: stm32: properly handle 0 byte transfer

[ Upstream commit 2269f5a8b1a7b38651d62676b98182828f29d11a ]

On 0 byte transfer request, return straight from the
xfer function after finalizing the transfer.

Fixes: dcbe0d84dfa5 ("spi: add driver for STM32 SPI controller")
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Link: https://lore.kernel.org/r/1612551572-495-2-git-send-email-alain.volmat@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 6017209..6eeb396 100644 (file)
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -1677,6 +1677,10 @@ static int stm32_spi_transfer_one(struct spi_master *master,
        struct stm32_spi *spi = spi_master_get_devdata(master);
        int ret;
 
+       /* Don't do anything on 0 bytes transfers */
+       if (transfer->len == 0)
+               return 0;
+
        spi->tx_buf = transfer->tx_buf;
        spi->rx_buf = transfer->rx_buf;
        spi->tx_len = spi->tx_buf ? transfer->len : 0;