[PATCH 6.18 128/752] spi: stm32: fix Overrun issue at < 8bpw

Sasha Levin
2026-02-28T17:49:56Z

From: Deepak Kumar <deepak.kumar01@st.com>

[ Upstream commit 1ac3be217c01d5df55ec5052f81e4f1708f46552 ]

When SPI communication is suspended by hardware automatically, it could
happen that few bits of next frame are already clocked out due to
internal synchronization delay.

To achieve a safe suspension, we need to ensure that each word must be
at least 8 SPI clock cycles long. That's why, if bpw is less than 8
bits, we need to use midi to reach 8 SPI clock cycles at least.

This will ensure that each word achieve safe suspension and prevent
overrun condition.

Signed-off-by: Deepak Kumar <deepak.kumar01@st.com>
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Link: https://patch.msgid.link/20251218-stm32-spi-enhancements-v2-2-3b69901ca9fe@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/spi/spi-stm32.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 2c804c1aef989..80986bd251d29 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -1906,11 +1906,12 @@ static void stm32h7_spi_data_idleness(struct stm32_spi *spi, struct spi_transfer
cfg2_clrb |= STM32H7_SPI_CFG2_MIDI;
if ((len > 1) && (spi->cur_midi > 0)) {
u32 sck_period_ns = DIV_ROUND_UP(NSEC_PER_SEC, spi->cur_speed);
- u32 midi = min_t(u32,
- DIV_ROUND_UP(spi->cur_midi, sck_period_ns),
- FIELD_GET(STM32H7_SPI_CFG2_MIDI,
- STM32H7_SPI_CFG2_MIDI));
+ u32 midi = DIV_ROUND_UP(spi->cur_midi, sck_period_ns);

+ if ((spi->cur_bpw + midi) < 8)
+ midi = 8 - spi->cur_bpw;
+
+ midi = min_t(u32, midi, FIELD_MAX(STM32H7_SPI_CFG2_MIDI));

dev_dbg(spi->dev, "period=%dns, midi=%d(=%dns)\n",
sck_period_ns, midi, midi * sck_period_ns);
--
2.51.0