From: Michael Walle <email@example.com> To: Rob Herring <firstname.lastname@example.org>, Krzysztof Kozlowski <email@example.com>, Nicolas Ferre <firstname.lastname@example.org>, Kavyasree Kotagiri <email@example.com> Cc: firstname.lastname@example.org, email@example.com Subject: Re: [PATCH] ARM: dts: lan966x: fix sys_clk frequency Date: Wed, 22 Jun 2022 13:51:21 +0200 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> 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 <firstname.lastname@example.org> > > 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. -michael
next prev parent reply other threads:[~2022-06-22 11:51 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 [this message] 2022-07-15 18:41 ` Michael Walle 2022-07-18 6:36 ` Claudiu.Beznea 2022-06-29 11:40 ` Kavyasree.Kotagiri
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