Re: [PATCH v2 1/3] PATA host controller driver for ep93xx

[Arnd Bergmann <arnd@xxxxxxxx>]

On Wednesday 04 April 2012, Rafal Prylowski wrote:
> On 2012-04-03 22:08, Arnd Bergmann wrote:
> >>> +static void ep93xx_pata_wait_for_iordy(void __iomem *base)
> >>> +{
> >>> +     unsigned long deadline = jiffies + msecs_to_jiffies(1000);
> >>> +     while (!ep93xx_pata_check_iordy(base) &&
> >>> +             time_is_before_jiffies(deadline))
> >>> +             cpu_relax();
> >>> +}
> > 
> > Much better for a delay than the previous version. However, it's
> > still a busy wait, which is bad for realtime behavior, especially
> > since this can potentially take many milliseconds. If possible,
> > it should have an msleep() or at least cond_resched() instead of
> > the cpu_relax(). Obviously that will only work when no spinlocks
> > are held.
> > 
> 
> Unfortunately, we can't use msleep() or cond_resched() here
> - ep93xx_pata_wait_for_iordy() is called from interrupt handler.

Well, it also seems inappropriate to have a one second delay timeout
inside of the interrupt handler.

I suppose if you are emulating what a regular read of the status
register does, there isn't much to improve here though.

	Arnd
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