linux-kernel - Re: [PATCH v5 05/17] clk: meson: g12a: make VCLK2 and ENCL clock path configurable by CCF

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Message-ID: <CAFBinCD4nZPp4JKpGARBkWL5pKVHJ0GSLTvy3S_q9mF=1d37Kg@mail.gmail.com>
Date:   Tue, 30 May 2023 21:36:09 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     neil.armstrong@...aro.org
Cc:     Jerome Brunet <jbrunet@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        "Lukas F. Hartmann" <lukas@...re.com>,
        Nicolas Belin <nbelin@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-phy@...ts.infradead.org
Subject: Re: [PATCH v5 05/17] clk: meson: g12a: make VCLK2 and ENCL clock path
 configurable by CCF

Hi Neil,

On Tue, May 30, 2023 at 5:57 PM Neil Armstrong
<neil.armstrong@...aro.org> wrote:
[...]
> >> The mipi_dsi_pxclk_div is set as RO in order to use the same GP0
> >> for mipi_dsi_pxclk and vclk2_input.
> >
> > I don't think notifiers is the appropriate approach here.
> > Whenever there is clock change the motifiers would trigger an off/on of
> > the clock, regardless of the clock usage or state.
> > If you have several consummers on this vclk2, this would
> > cause glitches and maybe this is not desirable.
> >
> > I think it would be better to handle the enable and reset with a
> > specific gate driver, in prepare() or enable(), and the give the clock
> > CLK_SET_RATE_GATE flag.
> >
> > This would require the clock to be properly turn off before changing the
> > rate.
>
> Sure, will see how to switch to that, seem Martin did than on Meson8.
You can start here: [0]
It may not be the nicest logic but so far it works (for me).

Please note that I don't mix between CCF and direct register IO clock handling:
For the old SoCs I'm relying only on CCF to manage the clocks.


Best regards,
Martin


[0] https://github.com/xdarklight/linux/blob/meson-mx-integration-6.3-20230410/drivers/gpu/drm/meson/meson_vclk.c#L1177-L1179