Hi--
On 2/20/21 3:02 PM, Tong Zhang wrote:
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.
Is this a real problem or theoretical? Does someone still use this driver?
Signed-off-by: Tong Zhang ztong0001@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)
drop void ^^^ It's already "int". Did you compile this?
+{
- int timeout = 10000;
- while (pm2_RD(p, PM2R_IN_FIFO_SPACE) < a) {
cpu_relax();if (--timeout==0)
spaces around ==
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;
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)
spaces around ==
goto end;}if (pm2_RD(par, PM2R_OUT_FIFO) == PM2TAG(PM2R_SYNC))break;- } while (--timeout_sync>0);
spaces around >
+end:
- if ((!timeout_sync) || (!timeout_fifo))
printk_ratelimited(KERN_WARNING "pm2fb: sync timeout!\n");}
thanks.