Re: [PATCH v3 3/4] serial: 8250_dw: Simplify the ref clock rate setting procedure

[Serge Semin]

On Fri, May 15, 2020 at 05:05:47PM +0300, Andy Shevchenko wrote:
> On Thu, May 07, 2020 at 02:31:34AM +0300, Serge Semin wrote:
> > Really instead of twice checking the clk_round_rate() return value
> > we could do it once, and if it isn't error the clock rate can be changed.
> > By doing so we decrease a number of ret-value tests and remove a weird
> > goto-based construction implemented in the dw8250_set_termios() method.
> 
> >  	rate = clk_round_rate(d->clk, baud * 16);
> > -	if (rate < 0)
> > -		ret = rate;
> 
> > -	else if (rate == 0)
> > -		ret = -ENOENT;
> 
> This case now handled differently.
> I don't think it's good idea to change semantics.
> 
> So, I don't see how this, after leaving the rate==0 case, would be better than
> original one.

Semantic doesn't change. The code does exactly the same as before. If it didn't
I either would have provided a comment about this or just didn't introduce the
change in the first place. I guess you just don't see the whole picture of the
method. Take a look in the code. The ret variable's been used to skip the
"p->uartclk = rate" assignment. That's it. So the (rate == 0) will still be
considered as error condition, which causes the clock rate left unchanged.
Here is the code diff so you wouldn't need to dive deep into the driver
sources:

<	clk_disable_unprepare(d->clk);
<	rate = clk_round_rate(d->clk, baud * 16);
<	if (rate < 0)
<		ret = rate;
<	else if (rate == 0)
<		ret = -ENOENT;
<	else
<		ret = clk_set_rate(d->clk, rate);
<	clk_prepare_enable(d->clk);
<
<	if (ret)
<		goto out;
<
<	p->uartclk = rate;
<
<out:
---
>       clk_disable_unprepare(d->clk);
>       rate = clk_round_rate(d->clk, baud * 16);
>       if (rate > 0) {
>              ret = clk_set_rate(d->clk, rate);
>              if (!ret)
>                      p->uartclk = rate;
>       }
>       clk_prepare_enable(d->clk);

-Sergey

> 
> > -	else
> > +	if (rate > 0) {
> >  		ret = clk_set_rate(d->clk, rate);
> > +		if (!ret)
> > +			p->uartclk = rate;
> > +	}
> >  	clk_prepare_enable(d->clk);
> >  
> > -	if (ret)
> > -		goto out;
> > -
> > -	p->uartclk = rate;
> > -
> > -out:
> >  	p->status &= ~UPSTAT_AUTOCTS;
> >  	if (termios->c_cflag & CRTSCTS)
> >  		p->status |= UPSTAT_AUTOCTS;
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>