[PATCH] spi: dw: use "smp_mb()" to avoid sending spi data error

From: Xinwei Kong
Date: Thu Jan 02 2020 - 21:52:10 EST

Because of out-of-order execution about some CPU architecture,
In this debug stage we find Completing spi interrupt enable ->
prodrucing TXEI interrupt -> running "interrupt_transfer" function
will prior to set "dw->rx and dws->rx_end" data, so this patch add
memory barrier to enable dw->rx and dw->rx_end to be visible and
solve to send SPI data error.
it will fix to this following low possibility error in testing environment
which using SPI control to connect TPM Modules

kernel: tpm tpm0: Operation Timed out
kernel: tpm tpm0: tpm_relinquish_locality: : error -1

Signed-off-by: fengsheng <fengsheng5@xxxxxxxxxx>
Signed-off-by: Xinwei Kong <kong.kongxinwei@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1578019930-55858-1-git-send-email-kong.kongxinwei@xxxxxxxxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
drivers/spi/spi-dw.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index c547ae38ed69..310492e21b33 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -297,6 +297,9 @@ static int dw_spi_transfer_one(struct spi_controller *master,
dws->len = transfer->len;
spin_unlock_irqrestore(&dws->buf_lock, flags);

+ /* Ensure dw->rx and dw->rx_end are visible */
+ smp_mb();
spi_enable_chip(dws, 0);

/* Handle per transfer options for bpw and speed */