Unverified Commit 1ac3be21 authored by Deepak Kumar's avatar Deepak Kumar Committed by Mark Brown
Browse files

spi: stm32: fix Overrun issue at < 8bpw 



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: default avatarDeepak Kumar <deepak.kumar01@st.com>
Signed-off-by: default avatarAlain Volmat <alain.volmat@foss.st.com>
Link: https://patch.msgid.link/20251218-stm32-spi-enhancements-v2-2-3b69901ca9fe@foss.st.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent c266d19b

drivers/spi/spi-stm32.c

+5 −4
Original line number Diff line number Diff line
@@ -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);