linux-kernel - Re: [PATCH] ARM: dts: lan966x: fix sys

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Message-ID: <69fdf542-e7ca-ffd1-3f73-ea8dca887a46@microchip.com>
Date:   Mon, 18 Jul 2022 06:36:48 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <michael@...le.cc>, <robh+dt@...nel.org>, <krzk+dt@...nel.org>,
        <Nicolas.Ferre@...rochip.com>, <Kavyasree.Kotagiri@...rochip.com>
CC:     <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: dts: lan966x: fix sys_clk frequency

On 15.07.2022 21:41, Michael Walle wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
> 
> [+ Claudiu as he seems to pick patches for at91, too]
> 
> Am 2022-06-22 13:51, schrieb Michael Walle:
>> Am 2022-04-28 10:49, schrieb Michael Walle:
>>> Am 2022-03-26 20:40, schrieb Michael Walle:
>>>> The sys_clk frequency is 165.625MHz. The register reference of the
>>>> Generic Clock controller lists the CPU clock as 600MHz, the DDR clock
>>>> as
>>>> 300MHz and the SYS clock as 162.5MHz. This is wrong. It was first
>>>> noticed during the fan driver development and it was measured and
>>>> verified via the CLK_MON output of the SoC which can be configured to
>>>> output sys_clk/64.
>>>>
>>>> The core PLL settings (which drives the SYS clock) seems to be as
>>>> follows:
>>>>   DIVF = 52
>>>>   DIVQ = 3
>>>>   DIVR = 1
>>>>
>>>> With a refernce clock of 25MHz, this means we have a post divider
>>>> clock
>>>>   Fpfd = Fref / (DIVR + 1) = 25MHz / (1 + 1) = 12.5MHz
>>>>
>>>> The resulting VCO frequency is then
>>>>   Fvco = Fpfd * (DIVF + 1) * 2 = 12.5MHz * (52 + 1) * 2 = 1325MHz
>>>>
>>>> And the output frequency is
>>>>   Fout = Fvco / 2^DIVQ = 1325MHz / 2^3 = 165.625Mhz
>>>>
>>>> This all adds up to the constrains of the PLL:
>>>>     10MHz <= Fpfd <= 200MHz
>>>>     20MHz <= Fout <= 1000MHz
>>>>   1000MHz <= Fvco <= 2000MHz
>>>>
>>>> Fixes: 290deaa10c50 ("ARM: dts: add DT for lan966 SoC and 2-port
>>>> board pcb8291")
>>>> Signed-off-by: Michael Walle <michael@...le.cc>

Applied to at91-fixes, thanks!

>>>
>>> Ping :)
>>>
>>> Btw. this is also true for the new B0 silicon. I just verified it
>>> with the CLK_MON output.
>>
>> Ping #2.
>>
>> Could this please be picked up because most drivers use this property
>> to calculate output frequencies and so on, e.g. the PWM driver.
> 
> Ping #3. Now it even got a Reviewed-by.
> 
> -michael