linux-kernel - Re: [PATCH] clk: sunxi-ng: v3s: add support for variable rate audio pll output

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Message-ID: <CAGb2v651jyoD9g25gv4+LoRDopNz2L7YYwp6O=GDNq4E0=HO7Q@mail.gmail.com>
Date:   Thu, 18 Feb 2021 16:08:09 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Tobias Schramm <t.schramm@...jaro.org>
Cc:     Maxime Ripard <maxime@...no.tech>, Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clk: sunxi-ng: v3s: add support for variable rate audio
 pll output

On Thu, Feb 18, 2021 at 4:06 PM Icenowy Zheng <icenowy@...c.io> wrote:
>
>
>
> 于 2021年2月18日 GMT+08:00 下午3:58:35, Maxime Ripard <maxime@...no.tech> 写到:
> >Hi,
> >
> >On Fri, Feb 12, 2021 at 02:57:25PM +0100, Tobias Schramm wrote:
> >> Previously the variable rate audio pll output was fixed to a divider
> >of
> >> four. This is unfortunately incompatible with generating commonly
> >used
> >> I2S core clock rates like 24.576MHz from the 24MHz parent clock.
> >> This commit adds support for arbitrary audio pll output dividers to
> >fix
> >> that.
> >>
> >> Signed-off-by: Tobias Schramm <t.schramm@...jaro.org>
> >
> >It's not really clear to me how that would help.
>
> We have introducee SDM-based accurate audio PLL on several
> other SoCs. Some people is quite sensitive about audio-related things.

Right. What you really want is the SDM-based fractional clock support.
Just look at the other drivers.

> >
> >The closest frequency we can provide for 24.576MHz would be 24580645
> >Hz,
> >with N = 127, M = 31 and P = 4, so it would work with what we have
> >already?

Correct. And that is still slightly off. It's even worse for the 44.1khz
family.

ChenYu

> >Maxime
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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