Re: bug in intelfbhw.c

["Antonino A. Daplas" <adaplas@gmail.com>]

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On Thu, 2007-02-22 at 09:14 +0100, Orczykowski, Juergen wrote:
> Hello,
> 
> we would like to use your drivers in our software. While debugging we
> found a bug in calculating the ring_space.
> 
> If there is less then RING_MIN_FREE available in the ring buffer,
> dinfo->ring_space is set to a big value forcing wait_ring to return.
> 
> We have attached a possible solution to solve this bug.
> 

Dave,

I created a patch based on the source.  I don't have the hardware so do
you want to look at this?

Tony

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intelfb: Fix ring space calculation

From: Orczykowski, Juergen <juergen.orczykowski@siemens.com>

If there is less then RING_MIN_FREE available in the ring buffer,
dinfo->ring_space is set to a big value forcing wait_ring to return.

Fix by making ring space = 0 if ring space < RING_MIN_FREE.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
---

 drivers/video/intelfb/intelfbhw.c |   27 ++++++++++++++++++++-------
 1 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/video/intelfb/intelfbhw.c b/drivers/video/intelfb/intelfbhw.c
index c1eb18b..05d07c1 100644
--- a/drivers/video/intelfb/intelfbhw.c
+++ b/drivers/video/intelfb/intelfbhw.c
@@ -1428,6 +1428,24 @@ static void refresh_ring(struct intelfb_
 static void reset_state(struct intelfb_info *dinfo);
 static void do_flush(struct intelfb_info *dinfo);
 
+static  u32 get_ring_space(struct intelfb_info *dinfo)
+{
+	u32 ring_space;
+
+	if (dinfo->ring_tail >= dinfo->ring_head)
+		ring_space = dinfo->ring.size -
+			(dinfo->ring_tail - dinfo->ring_head);
+	else
+		ring_space = dinfo->ring_head - dinfo->ring_tail;
+
+	if (ring_space > RING_MIN_FREE)
+		ring_space -= RING_MIN_FREE;
+	else
+		ring_space = 0;
+
+	return ring_space;
+}
+
 static int
 wait_ring(struct intelfb_info *dinfo, int n)
 {
@@ -1442,13 +1460,8 @@ #endif
 	end = jiffies + (HZ * 3);
 	while (dinfo->ring_space < n) {
 		dinfo->ring_head = INREG(PRI_RING_HEAD) & RING_HEAD_MASK;
-		if (dinfo->ring_tail + RING_MIN_FREE < dinfo->ring_head)
-			dinfo->ring_space = dinfo->ring_head
-				- (dinfo->ring_tail + RING_MIN_FREE);
-		else
-			dinfo->ring_space = (dinfo->ring.size +
-					     dinfo->ring_head)
-				- (dinfo->ring_tail + RING_MIN_FREE);
+		dinfo->ring_space = get_ring_space(dinfo);
+
 		if (dinfo->ring_head != last_head) {
 			end = jiffies + (HZ * 3);
 			last_head = dinfo->ring_head;

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