linux-kernel - Re: [PATCH v2 2/4] clk: meson-gxbb: Fix HDMI PLL for GXL SoCs

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Date:   Sun, 18 Nov 2018 13:48:37 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     jbrunet@...libre.com, linux-amlogic@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/4] clk: meson-gxbb: Fix HDMI PLL for GXL SoCs

Hi Neil,

On Tue, Nov 6, 2018 at 3:59 PM Neil Armstrong <narmstrong@...libre.com> wrote:
>
> In an attempt to better describe the HDMI PLL, a single DCO clock was
> left for GXBB and GXL, but the GXL DCO does not have a pre-multiplier.
>
> This patch adds back a GXL specific HDMI PLL DCO with xtal as parent.
according to the public S905X datasheet (from Khadas)
HHI_HDMI_PLL_CNTL2[31:30] describe the OD_FB
the 32-bit SoCs probably have an OD_FB as well and it seems that the
formula for the PLL with OD_FB is:
  in * m / n >> od << od_fb
(however, I must admit that I'm not sure where od_fb fits in best:
before the PLL DCO - like OD is after the PLL DCO, or part of the PLL
DCO)

so this is more of a question than a suggestion/feedback:
do you know whether the datasheet is correct and there's really a
programmable multiplier (called OD_FB)?
do you have more details on that topic?


Regards
Martin