linux-kernel - Re: [PATCH v2 0/3] clk: meson: rounding for fast clocks on 32-bit SoCs

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Message-ID: <CAFBinCBpkci-BeqLSN+BNbrcAE9sLKM8Hs0BB09AM1GKmtU9_g@mail.gmail.com>
Date:   Tue, 22 Jun 2021 23:04:55 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>, sboyd@...nel.org
Cc:     Neil Armstrong <narmstrong@...libre.com>, mturquette@...libre.com,
        khilman@...libre.com, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 0/3] clk: meson: rounding for fast clocks on 32-bit SoCs

Hi Stephen,

On Mon, Jun 7, 2021 at 9:04 AM Jerome Brunet <jbrunet@...libre.com> wrote:
>
>
> On Fri 04 Jun 2021 at 19:18, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:
>
> > Hi Jerome, Hi Stephen,
> >
> > On Mon, May 24, 2021 at 12:37 PM Martin Blumenstingl
> > <martin.blumenstingl@...glemail.com> wrote:
> >>
> >> On the 32-bit Amlogic Meson8/8b/8m2 SoCs we run into a problem with the
> >> fast HDMI PLL and it's OD (post-dividers). This clock tree can run at
> >> up to approx. 3GHz.
> >> This however causes a problem, because these rates require BIT(31) to
> >> be usable. Unfortunately this is not the case with clk_ops.round_rate
> >> on 32-bit systems. BIT(31) is reserved for the sign (+ or -).
> >>
> >> clk_ops.determine_rate does not suffer from this limitation. It uses
> >> an int to signal any errors and can then take all availble 32 bits for
> >> the clock rate.
> >>
> >> Changes since v1 from [0]:
> >> - reworked the first patch so the the existing
> >>   divider_{ro_}round_rate_parent implementations are using the new
> >>   divider_{ro_}determine_rate implementations to avoid code duplication
> >>   (thanks Jerome for the suggestion)
> >> - added a patch to switch the default clk_divider_{ro_}ops to use
> >>   .determine_rate instead of .round_rate as suggested by Jerome
> >>   (thanks)
> >> - dropped a patch for the Meson PLL ops as these are independent from
> >>   the divider patches and Jerome has applied that one directly (thanks)
> >> - added Jerome's Reviewed-by to the meson clk-regmap patch (thanks!)
> >> - dropped the RFC prefix
> > please let me know what you think about this v2
> > I am asking because clk-divider is widely used, so I'd appreciate if
> > this gets some time in linux-next (so for example Kernel CI can test
> > this and report issues if there are any).
Do you have any comments on this series?
I am fine with it skipping 5.14 as it's a change which affects
multiple platforms.
So I would like to use the time until the trees are opening for
patches targeting 5.15 to iron out code-review comments.

> Looks good to me
> Reviewed-by: Jerome Brunet <jbrunet@...libre.com>
Thanks Jerome - I'll add it to v3 once I send it (assuming nothing
major changes)


Best regards,
Martin