linux-kernel - Re: [PATCH 1/4] ARM: dts: r8a7742-iwg21d-q7: Enable PCIe Controller

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Message-ID: <CAMuHMdUAKeXWD=G0ifNkMehtdvZATyyiudPL103gp5nY-XMufA@mail.gmail.com>
Date:   Thu, 3 Sep 2020 13:29:43 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Magnus Damm <magnus.damm@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] ARM: dts: r8a7742-iwg21d-q7: Enable PCIe Controller

Hi Prabhakar,

On Thu, Sep 3, 2020 at 1:18 PM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
> On Thu, Sep 3, 2020 at 11:18 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Tue, Aug 25, 2020 at 6:28 PM Lad Prabhakar
> > <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> > > Enable PCIe Controller and set PCIe bus clock frequency.
> > >
> > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > Reviewed-by: Chris Paterson <Chris.Paterson2@...esas.com>
> >
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > i.e. will queue in renesas-devel for v5.10.
> >
> > One thing to double-check below.
> >
> > > --- a/arch/arm/boot/dts/r8a7742-iwg21d-q7.dts
> > > +++ b/arch/arm/boot/dts/r8a7742-iwg21d-q7.dts
> > > @@ -238,6 +238,18 @@
> > >         /* status = "okay"; */
> > >  };
> > >
> > > +&pcie_bus_clk {
> > > +       clock-frequency = <100000000>;
> > > +};
> > > +
> > > +&pciec {
> > > +       /* SW2[6] determines which connector is activated
> > > +        * ON = PCIe X4 (connector-J7)
> > > +        * OFF = mini-PCIe (connector-J26)
> >
> > The table on page 14 says it's the other way around.
> >
> > According to the CBTL02042ABQ datasheet, PCIe_SEL = low
> > selects the first channel (PCIe x4), while PCIe_SEL = high selects the
> > second channel (mini-PCIe).
> > Enabling the switch ties the signal low, so the table must be wrong.
> >
> Referring to [1] page 3:
>
> SEL = LOW: A↔B
> SEL = HIGH: A↔C
>
> And as per the schematic iW-PREJD-CS-01-R2.0-REL1.5.pdf channel B is
> J7 (PCIe X 4) and channel C is J26 (mini PCIe slot).
>
> Enabling the switch SW2[6] (ON) ties SEL to LOW -> channel B is J7 (PCIe X 4)
> Disabling the switch SW2[6] (OFF) ties SEL to HIGH -> channel C is J26
> (mini PCIe)
>
> Also iW-PREJD-CS-01-R2.0-REL1.5.pdf page 14 (General purpose table DIP
> Switch) mentions the above.

Oh right, I looked at the old document, and they fixed it in the newer one.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds