netdev - [PATCH v2] net: altera_tse: fix msgdma_tx_completion on non-zero fill

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Message-ID: <20190125.110222.956948485194493083.atsushi.nemoto@sord.co.jp>
Date:   Fri, 25 Jan 2019 11:02:22 +0900
From:   Atsushi Nemoto <atsushi.nemoto@...d.co.jp>
To:     Thor Thayer <thor.thayer@...ux.intel.com>, <netdev@...r.kernel.org>
CC:     Dalon L Westergreen <dalon.westergreen@...ux.intel.com>,
        Tomonori Sakita <tomonori.sakita@...d.co.jp>
Subject: [PATCH v2] net: altera_tse: fix msgdma_tx_completion on non-zero
 fill_level case

From: Tomonori Sakita <tomonori.sakita@...d.co.jp>

If fill_level was not zero and status was not BUSY,
result of "tx_prod - tx_cons - inuse" might be zero.
Subtracting 1 unconditionally results invalid negative return value
on this case.
Make sure not to return an negative value.

Signed-off-by: Tomonori Sakita <tomonori.sakita@...d.co.jp>
Signed-off-by: Atsushi Nemoto <atsushi.nemoto@...d.co.jp>
Reviewed-by: Dalon L Westergreen <dalon.westergreen@...ux.intel.com>
---
Changes in v2:
  Use max_t instead of just removing the "- 1".

 drivers/net/ethernet/altera/altera_msgdma.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/altera/altera_msgdma.c b/drivers/net/ethernet/altera/altera_msgdma.c
index 0fb986b..0ae723f 100644
--- a/drivers/net/ethernet/altera/altera_msgdma.c
+++ b/drivers/net/ethernet/altera/altera_msgdma.c
@@ -145,7 +145,8 @@ u32 msgdma_tx_completions(struct altera_tse_private *priv)
 			& 0xffff;
 
 	if (inuse) { /* Tx FIFO is not empty */
-		ready = priv->tx_prod - priv->tx_cons - inuse - 1;
+		ready = max_t(int,
+			      priv->tx_prod - priv->tx_cons - inuse - 1, 0);
 	} else {
 		/* Check for buffered last packet */
 		status = csrrd32(priv->tx_dma_csr, msgdma_csroffs(status));
-- 
2.1.4