linux-kernel - Re: [PATCH v2 1/2] clk: sunxi-ng: nkm: consider alternative parent rates when finding rate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <sfni3vehkhotsqrrirklhzrxzkcxzkq6nbtqokeab5if3jgm53@frh7z3iowsfe>
Date:   Mon, 12 Jun 2023 14:31:21 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Frank Oltmanns <frank@...manns.dev>
Cc:     Andre Przywara <andre.przywara@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Roman Beranek <me@...y.cz>,
        Samuel Holland <samuel@...lland.org>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v2 1/2] clk: sunxi-ng: nkm: consider alternative parent
 rates when finding rate

On Mon, Jun 12, 2023 at 10:51:52AM +0200, Frank Oltmanns wrote:
> > @@ -28,12 +68,17 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
> >  			for (_m = nkm->min_m; _m <= nkm->max_m; _m++) {
> 
> According to the manual M/N has to be <= 3. Therefore we need a
> different maximum value for the _m-for-loop:
> 
>         unsigned long max_m = min(3 * _n, nkm->max_m);
>         for (_m = nkm->min_m; _m <= max_m; _m++) {
> 
> I suggest that I add an optional member max_mn_ratio to the structs
> ccu_nkm and _ccu_nkm. Optional meaning: Ignore if 0.

Which workload is affected by this restriction?

> >  				unsigned long tmp_rate;
> >
> > -				tmp_rate = parent * _n * _k / _m;
> > -
> > +				if (parent_hw) {
> > +					tmp_parent = optimal_parent_rate(rate, _n, _k, _m);
> > +					tmp_parent = clk_hw_round_rate(parent_hw, tmp_parent);
> > +				}
> 
> Another constraint is PLL-VIDEO0 rate / M >= 24 MHz. Therefore we also need:
>         if (tmp_parent < 24000000 * _m)
>                 continue;
>
> So, we need another optional member min_m_times_parent or, for
> shortness, maybe min_m_parent. I could use help finding a good name for
> this.

Again, if it's not causing any harm I'd rather keep the code as simple
and maintainable as possible.

Maxime

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)