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SubjectRe: [PATCH] video: fbdev: pm2fb: avoid stall on fb_sync
Hi Randy,
Thanks for the comment.
I currently have this problem on my machine.
I have submitted a revised patch -- which includes the console log.
Thanks!
- Tong

On Sat, Feb 20, 2021 at 6:33 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> 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;
> > 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)
>
> 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");
> > return 0;
> > }
> >
> >
>
>
> thanks.
> --
> ~Randy

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