Re: [PATCH v3 01/12] serial: Store character timing information to uart_port

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

On Mon, Apr 11, 2022 at 01:52:18PM +0300, Andy Shevchenko wrote:
> On Mon, Apr 11, 2022 at 11:33:10AM +0300, Ilpo Järvinen wrote:
> > Struct uart_port currently stores FIFO timeout. Having character
> > timing information readily available is useful. Even serial core
> > itself determines char_time from port->timeout using inverse
> > calculation.
> > 
> > Store frame_time directly into uart_port. Character time is stored
> > in nanoseconds to have reasonable precision with high rates.
> > To avoid overflow, 64-bit math is necessary.
> > 
> > It might be possible to determine timeout from frame_time by
> > multiplying it with fifosize as needed but only part of the
> > users seem to be protected by a lock. Thus, this patch does
> > not pursue storing only frame_time in uart_port.

...

> > -	char_time = (port->timeout - HZ/50) / port->fifosize;
> > -	char_time = char_time / 5;
> > -	if (char_time == 0)
> > -		char_time = 1;
> > +	char_time = max(nsecs_to_jiffies(port->frame_time / 5), 1UL);
> > +
> >  	if (timeout && timeout < char_time)
> >  		char_time = timeout;
> 
> Seems it can be packed to something like
> 
> 	char_time = min_not_zero(nsecs_to_jiffies(port->frame_time / 5), timeout);
> 
> ?

Actually:

	char_time = min_not_zero(timeout, nsecs_to_jiffies(port->frame_time / 5));

Ah, either way it would still miss the case when both == 0. So, we need
something like minmax3_not_zero, where 1UL is implied argument. Probably
a suggesting for the future, since here it doesn't make much sense to
introduce.

-- 
With Best Regards,
Andy Shevchenko