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

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Date:   Mon, 07 Jun 2021 09:04:13 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.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


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).
>

Looks good to me
Reviewed-by: Jerome Brunet <jbrunet@...libre.com>

>
> Best regards,
> Martin