linux-kernel - Re: [linux-sunxi] [PATCH] clk: sunxi-ng: fix PLL

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Date:   Wed, 18 Jan 2017 18:48:35 +0100
From:   Ondřej Jirman <megous@...ous.com>
To:     maxime.ripard@...e-electrons.com
Cc:     dev@...ux-sunxi.org, Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jorik Jonker <jorik@...pendief.biz>,
        "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
        "moderated list:ARM/Allwinner sunXi SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [linux-sunxi] [PATCH] clk: sunxi-ng: fix PLL_CPUX adjusting on H3

Dne 18.1.2017 v 17:56 Maxime Ripard napsal(a):
>>> What's your current plan to fix that? I guess the easiest (and most
>>> likely to be reusable) would be to allow for clock tables, instead of
>>> using the generic approach. We might have some other clocks (like
>>> audio or video) that would need such a precise tuning in the future
>>> too.
>>
>> My proposed solution is this for M factor (H3 specific solution):
>>
>> https://github.com/megous/linux/commit/88be3d421e958579026135d8acec4b3983958738
> 
> This one is fine.
> 
>> and this for P factor:
>>
>> https://github.com/megous/linux/commit/d7f274ed0c13fa9b4099445cb6bf9b2f8f2cfa8a
>>
>> Perhaps it should be configurable if the P limitation is not universal
>> for all NKMP clocks. But I haven't read all the datasheets.
> 
> And this is exactly what I wanted to avoid, for the reason you're
> giving :)
> 
> This is some generic code, and yet you're putting a clock and SoC
> specific limit in there. You have two ways to deal with that. Either
> come up with some generic throttling mecanism to force a particular
> value above or below a given threshold, but that might be tedious to
> do, and require some significant rework.
> 
> Or you can use a table, which is generic and should be relatively
> easy. I really think this is the most straightforward solution, and
> even more so since we just want to support a limited number of
> frequencies in this case.

So I would add a pointer to a table to struct ccu_nkmp and define the
table itself in ccu-sun8i-h3.c?

If struct ccu_nkmp would have non-NULL pointer to a table, it would be
used instead of the math in ccu_nkmp.c.

Sounds ok?

regards,
  o.

> Maxime
>