Re: [PATCH v4 2/3] iio: adc: ti-ads1298: Fix incorrect timeout comment

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Sat, May 09, 2026 at 03:27:35PM -0500, David Lechner wrote:
> On 5/9/26 10:19 AM, Md Shofiqul Islam wrote:
> > At the lowest supported data rate of 250Hz, one conversion period is
> > 4ms, not 40ms. Fix the comment to correctly reflect the timing.
> > The 50ms timeout value itself is correct as a conservative margin.

...

> > -	/* Cannot take longer than 40ms (250Hz) */
> > +	/* Cannot take longer than 4ms at the lowest rate (250Hz) */
> >  	ret = wait_for_completion_timeout(&priv->completion, msecs_to_jiffies(50));
> 
> I would say "lowest sample rate" so we know which rate it is talking about.
> 
> However, there could be latency in the kernel delaying the interrupt from
> firing. The kernel latency can be much larger (I've seen 100s of ms on old
> single core ARM CPUs). So I think we should mention that in the comment as
> well so that no one is tempted to set it to msecs_to_jiffies(5) (or 4). Even
> if that works most of the time on a fast machine, we may need the longer
> timeout on slower machines.

Actually it's not about fast/slow machine, it's about scheduler and load.
Even on the fast machine under heavy load the completion (if it's thread
based) may take quite a significant time to be delivered. For the hard IRQ
based completions it might be much better case, but nowadays it's more of
a niche.

-- 
With Best Regards,
Andy Shevchenko