[U-Boot] [PATCH] mtd: nand: denali: Nuke unbounded loop

[Marek Vasut]

On Monday, December 21, 2015 at 11:32:09 AM, Masahiro Yamada wrote:
> Hi Marek,
> 
> 2015-12-21 19:16 GMT+09:00 Marek Vasut <marex at denx.de>:
> > On Monday, December 21, 2015 at 09:40:16 AM, Masahiro Yamada wrote:
> >> Hi Marek,
> > 
> > Hi,
> > 
> >> 2015-12-20 11:59 GMT+09:00 Marek Vasut <marex at denx.de>:
> >> > This particular unbounded loop in the Denali NAND reset routine can
> >> > lead to a system hang in case neither of the Timeout and Completed
> >> > bits get set.
> >> > 
> >> > Refactor the code a bit so it's readable and implement timer so the
> >> > loop is bounded instead. This way the complete hang can be prevented
> >> > even if the NAND fails to reset.
> >> > 
> >> > Signed-off-by: Marek Vasut <marex at denx.de>
> >> > Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
> >> > Cc: Scott Wood <scottwood at freescale.com>
> >> > ---
> >> > 
> >> >  drivers/mtd/nand/denali.c | 26 ++++++++++++++++++++------
> >> >  1 file changed, 20 insertions(+), 6 deletions(-)
> >> > 
> >> > diff --git a/drivers/mtd/nand/denali.c b/drivers/mtd/nand/denali.c
> >> > index 192be7d..8a8cca9 100644
> >> > --- a/drivers/mtd/nand/denali.c
> >> > +++ b/drivers/mtd/nand/denali.c
> >> > @@ -199,6 +199,7 @@ static void reset_bank(struct denali_nand_info
> >> > *denali)
> >> > 
> >> >  static uint32_t denali_nand_reset(struct denali_nand_info *denali)
> >> >  {
> >> >  
> >> >         int i;
> >> > 
> >> > +       u32 start, reg;
> >> > 
> >> >         for (i = 0; i < denali->max_banks; i++)
> >> >         
> >> >                 writel(INTR_STATUS__RST_COMP | INTR_STATUS__TIME_OUT,
> >> > 
> >> > @@ -206,12 +207,25 @@ static uint32_t denali_nand_reset(struct
> >> > denali_nand_info *denali)
> >> > 
> >> >         for (i = 0; i < denali->max_banks; i++) {
> >> >         
> >> >                 writel(1 << i, denali->flash_reg + DEVICE_RESET);
> >> > 
> >> > -               while (!(readl(denali->flash_reg + INTR_STATUS(i)) &
> >> > -                       (INTR_STATUS__RST_COMP |
> >> > INTR_STATUS__TIME_OUT))) -                       if
> >> > (readl(denali->flash_reg + INTR_STATUS(i)) & -                       
> >> >        INTR_STATUS__TIME_OUT)
> >> > -                               debug("NAND Reset operation timed out
> >> > on bank" -                                     " %d\n", i);
> >> > +
> >> > +               start = get_timer(0);
> >> > +               while (1) {
> >> > +                       reg = readl(denali->flash_reg +
> >> > INTR_STATUS(i)); +                       if (reg &
> >> > INTR_STATUS__TIME_OUT) {
> >> > +                               debug("NAND Reset operation timed out
> >> > on bank %d\n", +                                     i);
> >> > +                               break;
> >> > +                       }
> >> > +
> >> > +                       /* Reset completed and did not time out, all
> >> > good. */ +                       if (reg & INTR_STATUS__RST_COMP)
> >> > +                               break;
> >> > +
> >> > +                       if (get_timer(start) > (CONFIG_SYS_HZ / 1000))
> >> > { +                               debug("%s: Reset timed out!\n",
> >> > __func__); +                               break;
> >> > +                       }
> >> > +               }
> >> 
> >> I feel it is too much here
> >> about using get_timer() & CONFIG_SYS_HZ.
> >> 
> >> How about iterating udelay(1) up to reasonable times?
> > 
> > The get_timer() provides more precise delay , in this case, it's 1 sec .
> > Using just udelay() doesn't provide such precise control over the delay.
> 
> OK. Why do you want to wait precisely 1 sec.
> Rationale for "1 sec", please?

There isn't any, 1 second sounds about right for a timeout in my mind.

> > Moreover, I believe the get_timer() method is the one agreed upon for
> > implementing delays.
> 
> You do not have to use CONFIG_SYS_HZ.
> 
> As commented in lib/timer.c,
> get_timer() returns time in milliseconds.

Ah, so you'd prefer just 1000 in there instead ?

> >> See the  wait_for_irq() function in this file.
> > 
> > I'd like to convert this one to wait_for_bit() once that hits mainline.
> 
> No justice for the conversion.

It'd better to have one timeout function than multiple implementation of the
same thing in multiple drivers, that's all.

> This function just waits long enough,
> 1 sec, 2 sec, or whatever.