Re: [patch 02/13] mtd: SST25L (non JEDEC) SPI Flash driver

Ryan Mallon
2009-09-21T03:23:22Z

David Woodhouse wrote:
> On Fri, 2009-09-18 at 12:51 -0700, akpm@linux-foundation.org wrote:
>> +static int sst25l_wait_till_ready(struct sst25l_flash *flash)
>> +{
>> + unsigned long deadline;
>> + int status, err;
>> +
>> + deadline = jiffies + MAX_READY_WAIT_JIFFIES;
>> + do {
>> + err = sst25l_status(flash, &status);
>> + if (err)
>> + return err;
>> + if (!(status & SST25L_STATUS_BUSY))
>> + return 0;
>> +
>> + cond_resched();
>> + } while (!time_after_eq(jiffies, deadline));
>> +
>> + return -ETIMEDOUT;
>> +}
>
> If your system is busy and you end up relinquishing the CPU for a long
> period of time during that cond_resched(), you could hit the timeout
> condition even though the hardware _is_ actually reporting 'ready'
> status by the time you get back on the CPU.
>
> It's unlikely, admittedly, but it's good practice to make sure it can't
> happen like that. Something like
>
> while (busy) {
> if (timed_out) return -ETIMEDOUT;
> cond_resched();
> }
>

Okay, makes sense. I'm a bit busy at the moment, but I'll try and post a
fix in the next couple of days. Is the patch still going to be merged as
is, or are you waiting on a fix for this?

The function above is based on the one of the same name from
drivers/mtd/devices/m25p80.c, so that should also be changed? There are
possibly other mtd drivers which also have this construct.

~Ryan

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