linux-kernel - Re: [PATCH] clk: meson: Fix GXL HDMI PLL fractional bits width

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Message-ID: <CAFBinCCjmw=8ESk0tztWszXnuA4aqWqC8_wdpvMtSYfwZ-KT=A@mail.gmail.com>
Date:   Thu, 22 Nov 2018 23:05:48 +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] clk: meson: Fix GXL HDMI PLL fractional bits width

Hi Neil,

On Thu, Nov 22, 2018 at 9:26 AM Neil Armstrong <narmstrong@...libre.com> wrote:
>
> Hi Martin,
>
> On 21/11/2018 22:53, Martin Blumenstingl wrote:
> > Hi Neil,
> >
> > On Wed, Nov 21, 2018 at 12:19 PM Neil Armstrong <narmstrong@...libre.com> wrote:
> >>
> >> The GXL Documentation specifies 12 bits for the Fractional bit field,
> >> bit the last bits have a different purpose that we cannot handle right
> >> now, so update the bitwidth to have correct fractional calculations.
> > I assume you have more accurate documentation than what's available publicly:
> > - the S805 datasheet doesn't have any documentation for this register at all
> > - the S905 datasheet states that HHI_HDMI_PLL_CNTL2[11:0] are DIV_FRAC
> > - the S905X and S912 datasheets state that SDMNC_POWER is at
> > HHI_HDMI_PLL_CNTL2[6:0], SDMNC_ULMS is at HHI_HDMI_PLL_CNTL2[9:7] and
> > SSC_DEP_SEL is at HHI_HDMI_PLL_CNTL2[13:10]
> > - the S905X and S912 datasheets state that HHI_HDMI_PLL_CNTL1[11:0] are DIV_FRAC
>
> On S905, the HHI_HDMI_PLL_CNTL2 is at address 0xc9 << 2, but on S905X/S905D/S912 the
> equivalent register at same address is named HHI_HDMI_PLL_CNTL1.
>
> They changed the numbering of registers between these 2 SoCs, but the register
> content and addresses are similar for m/n/frac/reset.
I totally missed that - thanks for the explanation!

> >
> > can you confirm that the public S905X and S912 documentation is wrong
> > and that the .frac field is really part of HHI_HDMI_PLL_CNTL2 instead
> > of HHI_HDMI_PLL_CNTL1?
>
> Is is part of HHI_HDMI_PLL_CNTL1 but at address of S905 HHI_HDMI_PLL_CNTL2.
>
> When jerome pushed the PLL support earlier, he added a comment.
> I simply forgot to put it back when I added back the GXL HDMI PLL DCO.
I'm curious: do you know whether the fractional divider field on
Meson8b is 10 or 12 bits wide?

if you can add a short note about the naming confusion to the patch
description when applying the patch:
Acked-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>


Regards
Martin