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

[Masahiro Yamada]

Hi Marek,


2015-12-21 19:45 GMT+09:00 Marek Vasut <marex at denx.de>:
> 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 ?


Yes.


>> >> 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.


I noticed one thing I had missed.

While the CPU is stuck in udelay() function,
it cannot check the register flag that might have been already set.
This possibly wastes a small piece of time slice.

So, I am OK with your way
(and also with your next patch for the wait_for_bit() conversion, if you like).

Go ahead!


-- 
Best Regards
Masahiro Yamada