linux-kernel - Re: [PATCH v2] clk: at91: fix programmable clock for sama5d2

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Message-ID: <20190319092438.GC29054@piout.net>
Date:   Tue, 19 Mar 2019 10:24:38 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Nicolas.Ferre@...rochip.com
Cc:     sboyd@...nel.org, linux-clk@...r.kernel.org,
        Ludovic.Desroches@...rochip.com, Claudiu.Beznea@...rochip.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mturquette@...libre.com, matthias.wieloch@...-bauer.de,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] clk: at91: fix programmable clock for sama5d2

On 19/03/2019 08:28:40+0000, Nicolas Ferre wrote:
> > Ok. I can apply this clk-fixes. I presume that things are real bad and
> > it can't wait until v5.2?
> 
> To be perfectly clear, it's not a regression.
> But as we're at the very beginning of the '-rc' phase and as it's a bug, 
> I was thinking about adding it now. But you to choose, no problem either 
> way.
> 
> >> @@ -60,10 +68,18 @@ static int clk_programmable_determine_rate(struct clk_hw *hw,
> >>                          continue;
> >>   
> >>                  parent_rate = clk_hw_get_rate(parent);
> >> -               for (shift = 0; shift < PROG_PRES_MASK; shift++) {
> >> -                       tmp_rate = parent_rate >> shift;
> >> -                       if (tmp_rate <= req->rate)
> >> -                               break;
> >> +               if (layout->is_pres_direct) {
> >> +                       for (shift = 0; shift <= layout->pres_mask; shift++) {
> >> +                               tmp_rate = parent_rate / (shift + 1);
> >> +                               if (tmp_rate <= req->rate)
> >> +                                       break;
> >> +                       }
> >> +               } else {
> >> +                       for (shift = 0; shift < layout->pres_mask; shift++) {
> >> +                               tmp_rate = parent_rate >> shift;
> >> +                               if (tmp_rate <= req->rate)
> >> +                                       break;
> >> +                       }
> > 
> > This looks like a lot of copy paste when the if statement could have been
> > pulled into the for loop instead of duplicating the loops and
> > surrounding if condition check for tmp_rate.
> 
> Stop condition of loops not being the same made me separate them instead 
> of adding artificial test conditions for shift == layout->pres_mask. I'm 
> not sure the other way around is more obvious then...
> 

I also tried different ways (e.g. setting up a different determine_rate
for the sama5d2) but this ended up being the more concise one.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com