[PATCH net-next] net: qca_spi: Add available buffer space verification

[Stefan Wahren]

Interferences on the SPI line could distort the response of
available buffer space. So at least we should check that the
response doesn't exceed the maximum available buffer space.
In error case increase a new error counter and retry it later.
This behavior avoids buffer errors in the QCA7000, which
results in an unnecessary chip reset including packet loss.

Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
---
 drivers/net/ethernet/qualcomm/qca_debug.c |  1 +
 drivers/net/ethernet/qualcomm/qca_spi.c   | 16 +++++++++++++++-
 drivers/net/ethernet/qualcomm/qca_spi.h   |  1 +
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/qualcomm/qca_debug.c b/drivers/net/ethernet/qualcomm/qca_debug.c
index a9f1bc0..1450f38 100644
--- a/drivers/net/ethernet/qualcomm/qca_debug.c
+++ b/drivers/net/ethernet/qualcomm/qca_debug.c
@@ -61,6 +61,7 @@ static const char qcaspi_gstrings_stats[][ETH_GSTRING_LEN] = {
 	"Transmit ring full",
 	"SPI errors",
 	"Write verify errors",
+	"Buffer available errors",
 };
 
 #ifdef CONFIG_DEBUG_FS
diff --git a/drivers/net/ethernet/qualcomm/qca_spi.c b/drivers/net/ethernet/qualcomm/qca_spi.c
index d531050..97f9295 100644
--- a/drivers/net/ethernet/qualcomm/qca_spi.c
+++ b/drivers/net/ethernet/qualcomm/qca_spi.c
@@ -289,6 +289,14 @@ qcaspi_transmit(struct qcaspi *qca)
 
 	qcaspi_read_register(qca, SPI_REG_WRBUF_SPC_AVA, &available);
 
+	if (available > QCASPI_HW_BUF_LEN) {
+		/* This could only happen by interferences on the SPI line.
+		 * So retry later ...
+		 */
+		qca->stats.buf_avail_err++;
+		return -1;
+	}
+
 	while (qca->txr.skb[qca->txr.head]) {
 		pkt_len = qca->txr.skb[qca->txr.head]->len + QCASPI_HW_PKT_LEN;
 
@@ -355,7 +363,13 @@ qcaspi_receive(struct qcaspi *qca)
 	netdev_dbg(net_dev, "qcaspi_receive: SPI_REG_RDBUF_BYTE_AVA: Value: %08x\n",
 		   available);
 
-	if (available == 0) {
+	if (available > QCASPI_HW_BUF_LEN) {
+		/* This could only happen by interferences on the SPI line.
+		 * So retry later ...
+		 */
+		qca->stats.buf_avail_err++;
+		return -1;
+	} else if (available == 0) {
 		netdev_dbg(net_dev, "qcaspi_receive called without any data being available!\n");
 		return -1;
 	}
diff --git a/drivers/net/ethernet/qualcomm/qca_spi.h b/drivers/net/ethernet/qualcomm/qca_spi.h
index 2d2c497..eb9af45 100644
--- a/drivers/net/ethernet/qualcomm/qca_spi.h
+++ b/drivers/net/ethernet/qualcomm/qca_spi.h
@@ -74,6 +74,7 @@ struct qcaspi_stats {
 	u64 ring_full;
 	u64 spi_err;
 	u64 write_verify_failed;
+	u64 buf_avail_err;
 };
 
 struct qcaspi {
-- 
2.7.4