[v2,2/5] spi: stm32: fix fifo threshold level in case of short transfer

Commit Message

Alain Volmat Aug. 10, 2020, 7:12 a.m. UTC

From: Amelie Delaunay <[e-mail]>

When transfer is shorter than half of the fifo, set the data packet size
up to transfer size instead of up to half of the fifo.
Check also that threshold is set at least to 1 data frame.

Signed-off-by: Amelie Delaunay <[e-mail]>
Signed-off-by: Alain Volmat <[e-mail]>
---
v2: fix conditional statement

 drivers/spi/spi-stm32.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

Comments

Ludwig Zenz Sept. 14, 2020, 10:33 a.m. UTC | #1

> When transfer is shorter than half of the fifo, set the data packet size
> up to transfer size instead of up to half of the fifo.
> Check also that threshold is set at least to 1 data frame.

Through a git-bisect we have identified this patch as problematic. We have an application that uses a SPI protocol with telegrams of length 2 to 16 bytes. Due to this patch we have errors in the data transfer of the MOSI direction. We use SPI in PIO mode.

Please explain what this patch should improve or what exactly is changed in the behaviour.

best regards,
Ludwig Zenz

Patch

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 814a3ec3b8ad..e5450233f3f8 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -467,20 +467,27 @@  static int stm32_spi_prepare_mbr(struct stm32_spi *spi, u32 speed_hz,
 /**
  * stm32h7_spi_prepare_fthlv - Determine FIFO threshold level
  * @spi: pointer to the spi controller data structure
+ * @xfer_len: length of the message to be transferred
  */
-static u32 stm32h7_spi_prepare_fthlv(struct stm32_spi *spi)
+static u32 stm32h7_spi_prepare_fthlv(struct stm32_spi *spi, u32 xfer_len)
 {
-	u32 fthlv, half_fifo;
+	u32 fthlv, half_fifo, packet;
 
 	/* data packet should not exceed 1/2 of fifo space */
 	half_fifo = (spi->fifo_size / 2);
 
+	/* data_packet should not exceed transfer length */
+	if (half_fifo > xfer_len)
+		packet = xfer_len;
+	else
+		packet = half_fifo;
+
 	if (spi->cur_bpw <= 8)
-		fthlv = half_fifo;
+		fthlv = packet;
 	else if (spi->cur_bpw <= 16)
-		fthlv = half_fifo / 2;
+		fthlv = packet / 2;
 	else
-		fthlv = half_fifo / 4;
+		fthlv = packet / 4;
 
 	/* align packet size with data registers access */
 	if (spi->cur_bpw > 8)
@@ -488,6 +495,9 @@  static u32 stm32h7_spi_prepare_fthlv(struct stm32_spi *spi)
 	else
 		fthlv -= (fthlv % 4); /* multiple of 4 */
 
+	if (!fthlv)
+		fthlv = 1;
+
 	return fthlv;
 }
 
@@ -1393,7 +1403,7 @@  static void stm32h7_spi_set_bpw(struct stm32_spi *spi)
 	cfg1_setb |= (bpw << STM32H7_SPI_CFG1_DSIZE_SHIFT) &
 		     STM32H7_SPI_CFG1_DSIZE;
 
-	spi->cur_fthlv = stm32h7_spi_prepare_fthlv(spi);
+	spi->cur_fthlv = stm32h7_spi_prepare_fthlv(spi, spi->cur_xferlen);
 	fthlv = spi->cur_fthlv - 1;
 
 	cfg1_clrb |= STM32H7_SPI_CFG1_FTHLV;
@@ -1588,6 +1598,8 @@  static int stm32_spi_transfer_one_setup(struct stm32_spi *spi,
 
 	spin_lock_irqsave(&spi->lock, flags);
 
+	spi->cur_xferlen = transfer->len;
+
 	if (spi->cur_bpw != transfer->bits_per_word) {
 		spi->cur_bpw = transfer->bits_per_word;
 		spi->cfg->set_bpw(spi);
@@ -1635,8 +1647,6 @@  static int stm32_spi_transfer_one_setup(struct stm32_spi *spi,
 			goto out;
 	}
 
-	spi->cur_xferlen = transfer->len;
-
 	dev_dbg(spi->dev, "transfer communication mode set to %d\n",
 		spi->cur_comm);
 	dev_dbg(spi->dev,