[PATCH] spi: spacemit: Correct TX FIFO slot calculation

[Zhengyu He]

In k1_spi_write, the count variable is intended to represent the number
of slots available for writing into the TX FIFO.

The current implementation uses FIELD_GET(SSP_STATUS_TFL, val) in an
attempt to determine this count, but this register field returns the
number of occupied slots, not the available space. The previous
implementation attempted to handle this via a ternary operator (? :
K1_SPI_FIFO_SIZE), which incorrectly assumed that the hardware returned
0 when the FIFO was empty (meaning all slots were available), leading to
incorrect accounting of the buffer space.

Fix this by calculating the free slots: count = K1_SPI_FIFO_SIZE -
FIELD_GET(SSP_STATUS_TFL, val);

The associated comment has been updated to reflect the logic change: The
old comment reflected an incorrect assumption about the hardware
behavior, which was the root cause of the previous buggy logic.

This patch accurately and concisely describes the purpose of the new
calculation.

Signed-off-by: Peixin Xie <peixin.xie@xxxxxxxxxxxx>
Signed-off-by: Zhengyu He <hezhy472013@xxxxxxxxx>
---
 drivers/spi/spi-spacemit-k1.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-spacemit-k1.c b/drivers/spi/spi-spacemit-k1.c
index 215fe66d27b4..0faf7ffed676 100644
--- a/drivers/spi/spi-spacemit-k1.c
+++ b/drivers/spi/spi-spacemit-k1.c
@@ -494,8 +494,8 @@ static bool k1_spi_write(struct k1_spi_driver_data *drv_data, u32 val)
 {
 	unsigned int count;
 
-	/* Get the number of open slots in the FIFO; zero means all */
-	count = FIELD_GET(SSP_STATUS_TFL, val) ? : K1_SPI_FIFO_SIZE;
+	/* Get the number of free slots in the FIFO */
+	count = K1_SPI_FIFO_SIZE - FIELD_GET(SSP_STATUS_TFL, val);
 
 	/*
 	 * Limit how much we try to send at a time, to reduce the

---
base-commit: 51ed53630915c9cc290036fe4f430849e23bbf8e
change-id: 20260715-k1-spi-tx-fifo-fix-v1-for-next-43cdd0d9213f

Best regards,
-- 
Zhengyu He <hezhy472013@xxxxxxxxx>