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spi: stm32: fix Overrun issue at < 8bpw

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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>
This commit is contained in:
Deepak Kumar 2025-12-18 11:48:28 +01:00 committed by Mark Brown
parent c266d19b7d
commit 1ac3be217c
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1 changed files with 5 additions and 4 deletions
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9
drivers/spi/spi-stm32.c
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@ -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);