linux-kernel - [PATCH 3.2 012/125] matroxfb: perform a dummy read of M

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Message-ID: <lsq.1404846110.273575946@decadent.org.uk>
Date:	Tue, 08 Jul 2014 20:01:50 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Tomi Valkeinen" <tomi.valkeinen@...com>,
	"Mikulas Patocka" <mpatocka@...hat.com>
Subject: [PATCH 3.2 012/125] matroxfb: perform a dummy read of M_STATUS

3.2.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@...hat.com>

commit 972754cfaee94d6e25acf94a497bc0a864d91b7e upstream.

I had occasional screen corruption with the matrox framebuffer driver and
I found out that the reason for the corruption is that the hardware
blitter accesses the videoram while it is being written to.

The matrox driver has a macro WaitTillIdle() that should wait until the
blitter is idle, but it sometimes doesn't work. I added a dummy read
mga_inl(M_STATUS) to WaitTillIdle() to fix the problem. The dummy read
will flush the write buffer in the PCI chipset, and the next read of
M_STATUS will return the hardware status.

Since applying this patch, I had no screen corruption at all.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/video/fbdev/matrox/matroxfb_base.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/video/matrox/matroxfb_base.h
+++ b/drivers/video/matrox/matroxfb_base.h
@@ -698,7 +698,7 @@ void matroxfb_unregister_driver(struct m

 #define mga_fifo(n)	do {} while ((mga_inl(M_FIFOSTATUS) & 0xFF) < (n))

-#define WaitTillIdle()	do {} while (mga_inl(M_STATUS) & 0x10000)
+#define WaitTillIdle()	do { mga_inl(M_STATUS); do {} while (mga_inl(M_STATUS) & 0x10000); } while (0)

 /* code speedup */
 #ifdef CONFIG_FB_MATROX_MILLENIUM

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