From 2269f5a8b1a7b38651d62676b98182828f29d11a Mon Sep 17 00:00:00 2001
From: Alain Volmat <alain.volmat@foss.st.com>
Date: Fri, 5 Feb 2021 19:59:25 +0100
Subject: [PATCH] spi: stm32: properly handle 0 byte transfer
Git-commit: 2269f5a8b1a7b38651d62676b98182828f29d11a
Patch-mainline: v5.12-rc1
References: git-fixes

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/spi/spi-stm32.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index db3e305d9ec4..6cdecd1c5ec7 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -1657,6 +1657,10 @@ 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;
-- 
2.26.2