[PATCH] video: fbdev: pm2fb: avoid stall on fb_sync

[Tong Zhang]

pm2fb_sync is called when doing /dev/fb read or write.
The original pm2fb_sync wait indefinitely on hardware flags which can
possibly stall kernel and make everything unresponsive.
Instead of waiting indefinitely, we can timeout to give user a chance to
get back control.

Signed-off-by: Tong Zhang <ztong0...@gmail.com>
---
 drivers/video/fbdev/pm2fb.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c
index 27893fa139b0..8578c64a0c54 100644
--- a/drivers/video/fbdev/pm2fb.c
+++ b/drivers/video/fbdev/pm2fb.c
@@ -183,12 +183,23 @@ static inline void pm2v_RDAC_WR(struct pm2fb_par *p, s32 
idx, u32 v)
 
 #ifdef CONFIG_FB_PM2_FIFO_DISCONNECT
 #define WAIT_FIFO(p, a)
+#define WAIT_FIFO_TIMEOUT(p, a) (0)
 #else
 static inline void WAIT_FIFO(struct pm2fb_par *p, u32 a)
 {
        while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a)
                cpu_relax();
 }
+static int inline void WAIT_FIFO_TIMEOUT(struct pm2fb_par *p, u32 a)
+{
+       int timeout = 10000;
+       while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) {
+               cpu_relax();
+               if (--timeout==0)
+                       return 1;
+       }
+       return 0;
+}
 #endif
 
 /*
@@ -1031,15 +1042,27 @@ static int pm2fb_blank(int blank_mode, struct fb_info 
*info)
 static int pm2fb_sync(struct fb_info *info)
 {
        struct pm2fb_par *par = info->par;
+       int timeout_sync = 10000;
+       int timeout_fifo;
 
-       WAIT_FIFO(par, 1);
+       if (WAIT_FIFO_TIMEOUT(par, 1))
+               goto end;
        pm2_WR(par, PM2R_SYNC, 0);
        mb();
        do {
-               while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0)
+               timeout_fifo = 10000;
+               while (pm2_RD(par, PM2R_OUT_FIFO_WORDS) == 0) {
                        cpu_relax();
-       } while (pm2_RD(par, PM2R_OUT_FIFO) != PM2TAG(PM2R_SYNC));
+                       if (--timeout_fifo==0)
+                               goto end;
+               }
+               if (pm2_RD(par, PM2R_OUT_FIFO) == PM2TAG(PM2R_SYNC))
+                       break;
+       } while (--timeout_sync>0);
 
+end:
+       if ((!timeout_sync) || (!timeout_fifo))
+               printk_ratelimited(KERN_WARNING "pm2fb: sync timeout!\n");
        return 0;
 }
 
-- 
2.25.1