[U-Boot] PATCH mtd CFI flash: timeout calculation underflow if imprecise 1kHz timer: fix

[Shinya Kuribayashi <skuribay@pobox.com>]

Renato Andreola wrote:
>  From 21d84ab72266f118794233176bd356d8b1cfdf35 Mon Sep 17 00:00:00 2001
> From: Renato Andreola <renato.andreola@imagos.it>
> Date: Fri, 21 Aug 2009 18:05:51 +0200
> Subject: [PATCH] drivers/mtd/cfi_flash: precision and underflow problem in tout calculation
> 
> With old configuration it could happen tout=0 if CONFIG_SYS_HZ<1000.
> 
> Signed-off-by: Alessandro Rubini <rubini@gnudd.com> Renato Andreola <renato.andreola@imagos.it>
> ---
>   drivers/mtd/cfi_flash.c |    8 +++++---
>   1 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/cfi_flash.c b/drivers/mtd/cfi_flash.c
> index 81ac5d3..0d8fc54 100644
> --- a/drivers/mtd/cfi_flash.c
> +++ b/drivers/mtd/cfi_flash.c
> @@ -660,9 +660,11 @@ static int flash_status_check (flash_info_t * info, flash_sect_t sector,
>   	ulong start;
> 
>   #if CONFIG_SYS_HZ != 1000
> -	tout *= CONFIG_SYS_HZ/1000;
> -#endif
> -
> +	if ((ulong)CONFIG_SYS_HZ > 100000)
> +		tout *= (ulong)CONFIG_SYS_HZ/1000;  /* for a big HZ, avoid overflow */
> +	else
> +		tout = DIV_ROUND_UP(tout*(ulong)CONFIG_SYS_HZ, 1000);
> +#endif	
>   	/* Wait for command completion */
>   	start = get_timer (0);
>   	while (flash_is_busy (info, sector)) {

What should to be fixed first in this case, would be your CONFIG_SYS_HZ
setting, that is NIOS2? timer implementation, yeah really.  But I would
also point out that there is another case flash_status_check() doensn't
work as expected.

One of my colleagues found that with some flash device(s) (I don't
recall precisely, sorry), 'tout' would be probed to be zero.  In that
case, a workaround something like above still doesn't work.

We have not sorted out where the problem is; it might be in cfi_flash.c,
or in the flash device itself.  This is observed with v2009.03 release,
and we've been having a workaround for it for months.  I'd like to have
a look someday.

Anyway, checking to see if 'tout' is zero or not would be sometimes
worth a try, when you think cfi_flash.c doesn't work as expected.

Just for your information,