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From: Michael Walle <michael@walle.cc>
To: Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Kavyasree Kotagiri <kavyasree.kotagiri@microchip.com>,
	Claudiu.Beznea@microchip.com
Cc: devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ARM: dts: lan966x: fix sys_clk frequency
Date: Fri, 15 Jul 2022 20:41:06 +0200	[thread overview]
Message-ID: <ad62beb5a2c8582014a3b4172d55bf64@walle.cc> (raw)
In-Reply-To: <1d2cbab375b50c0be31780f2d8d7a088@walle.cc>

[+ 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@walle.cc>
>> 
>> 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

  reply	other threads:[~2022-07-15 18:41 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-26 19:40 Michael Walle
2022-04-28  8:49 ` Michael Walle
2022-06-22 11:51   ` Michael Walle
2022-07-15 18:41     ` Michael Walle [this message]
2022-07-18  6:36       ` Claudiu.Beznea
2022-06-29 11:40 ` Kavyasree.Kotagiri

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