[PATCH v2 1/6] spi: spi-sun4i: sun4i_spi_transfer_one(): fix transfers for SUN4I_FIFO_DEPTH

From: Marc Kleine-Budde <mkl@pengutronix.de>

In commit 6d9fe44bd73d ("spi: sun4i: fix FIFO limit"), the TX-FIFO is
filled max to SUN4I_FIFO_DEPTH - 1 (= 63) bytes to work around timeouts
observed on A10s SoCs.

Commit 196737912da5 ("spi: sun4i: Allow transfers larger than FIFO
size") added support for transfers larger than the FIFO size. But this
commit only enabled the TX-FIFO empty interrupt for transfers larger
than the FIFO (= 64) bytes.

This breaks transfers with exactly 64 bytes: the TX-FIFO is only filled
with 63 bytes but the interrupt to refill the FIFO is not triggered. The
problem can be reproduced with the following command:

| spidev_test -D /dev/spidev0.1 -S 64 -s 20000000 -I 1
|
| [ 7797.548745] spi_master spi0: spi0.1: timeout transferring 64 bytes@20000000Hz for 110(100)ms
| [ 7797.557237] spidev spi0.1: SPI transfer failed: -110
| [ 7797.562308] spi_master spi0: failed to transfer one message from queue
| [ 7797.568936] spi_master spi0: noqueue transfer failed

To fix the problem enable the TX-FIFO interrupt if the total TX length
is larger than SUN4I_FIFO_DEPTH - 1 (= 63) bytes.

Fixes: 196737912da5 ("spi: sun4i: Allow transfers larger than FIFO size")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Jonas Rebmann <redacted>
---
 drivers/spi/spi-sun4i.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index d5c16392cd4d..2e2324453905 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c

@@ -322,7 +322,7 @@ static int sun4i_spi_transfer_one(struct spi_controller *host,
 	sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC |
 					 SUN4I_INT_CTL_RF_F34);
 	/* Only enable Tx FIFO interrupt if we really need it */
-	if (tx_len > SUN4I_FIFO_DEPTH)
+	if (tx_len > SUN4I_FIFO_DEPTH - 1)
 		sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
 
 	/* Start the transfer */

-- 
2.55.0.123.gf60db8d575