[PATCH 2/4] spi: dw: use "smp_mb()" to avoid sending spi data error

[Ike Panhc]

From: Xinwei Kong <kong.kongxinwei at hisilicon.com>

BugLink: https://launchpad.net/bugs/1859744

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.
eg:
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 at huawei.com>
Signed-off-by: Xinwei Kong <kong.kongxinwei at hisilicon.com>
Link: https://lore.kernel.org/r/1578019930-55858-1-git-send-email-kong.kongxinwei@hisilicon.com
Signed-off-by: Mark Brown <broonie at kernel.org>
(cherry picked from commit bfda044533b213985bc62bd7ca96f2b984d21b80)
Signed-off-by: Ike Panhc <ike.pan at canonical.com>
---
 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 45972056ed8c..36e02f2f25c5 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c
@@ -289,6 +289,9 @@ static int dw_spi_transfer_one(struct spi_controller *master,
 	dws->rx_end = dws->rx + transfer->len;
 	dws->len = transfer->len;
 
+	/* Ensure dw->rx and dw->rx_end are visible */
+	smp_mb();
+
 	spi_enable_chip(dws, 0);
 
 	/* Handle per transfer options for bpw and speed */
-- 
2.17.1