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

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Message-ID: <CAFBinCDn_0TeyLG9b9uB+4-4PdeNXgja11wf2CGcQ99tUNjkyQ@mail.gmail.com>
Date:   Fri, 4 Jun 2021 19:18:40 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     sboyd@...nel.org, jbrunet@...libre.com
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 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).


Best regards,
Martin