linux-kernel - [PATCH] memstick: r592: avoid gcc-6 warning

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Date:	Tue, 15 Mar 2016 22:45:22 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Quentin Lambert <lambert.quentin@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] memstick: r592: avoid gcc-6 warning

The r592 driver relies on behavior of the DMA mapping API that is
normally observed but not guaranteed by the API. Instead it uses
a runtime check to fail transfers if the API ever behaves
differently.

When CONFIG_NEED_SG_DMA_LENGTH is not set, one of the checks turns
into a comparison of a variable with itself, which gcc-6.0 now
warns about:

drivers/memstick/host/r592.c: In function 'r592_transfer_fifo_dma':
drivers/memstick/host/r592.c:302:31: error: self-comparison always evaluates to false [-Werror=tautological-compare]
    (sg_dma_len(&dev->req->sg) < dev->req->sg.length)) {
                               ^

The check itself is not a problem, so this patch just rephrases
the condition in a way that gcc does not consider an indication
of a mistake. We already know that dev->req->sg.length was initially
R592_LFIFO_SIZE, so we can compare it to that constant again.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/memstick/host/r592.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/memstick/host/r592.c b/drivers/memstick/host/r592.c
index ef09ba0289d7..d5cfb503b9d6 100644
--- a/drivers/memstick/host/r592.c
+++ b/drivers/memstick/host/r592.c
@@ -298,8 +298,7 @@ static int r592_transfer_fifo_dma(struct r592_device *dev)
 	sg_count = dma_map_sg(&dev->pci_dev->dev, &dev->req->sg, 1, is_write ?
 		PCI_DMA_TODEVICE : PCI_DMA_FROMDEVICE);
 
-	if (sg_count != 1 ||
-			(sg_dma_len(&dev->req->sg) < dev->req->sg.length)) {
+	if (sg_count != 1 || sg_dma_len(&dev->req->sg) < R592_LFIFO_SIZE) {
 		message("problem in dma_map_sg");
 		return -EIO;
 	}
-- 
2.7.0