linux-kernel - Re: [PATCH v14 6/8] arm64: dts: Add AMD Pensando Elba SoC support

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Date:   Wed, 31 May 2023 15:09:28 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Brad Larson <blarson@....com>
Cc:     adrian.hunter@...el.com, alcooperx@...il.com,
        andy.shevchenko@...il.com, arnd@...db.de,
        brendan.higgins@...ux.dev, briannorris@...omium.org,
        broonie@...nel.org, catalin.marinas@....com, conor+dt@...nel.org,
        davidgow@...gle.com, devicetree@...r.kernel.org,
        fancer.lancer@...il.com, gerg@...ux-m68k.org, gsomlo@...il.com,
        hal.feng@...rfivetech.com, hasegawa-hitomi@...itsu.com,
        j.neuschaefer@....net, joel@....id.au, kernel@...il.dk,
        krzk@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        lee.jones@...aro.org, lee@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-spi@...r.kernel.org,
        michal.simek@....com, p.zabel@...gutronix.de,
        rdunlap@...radead.org, robh+dt@...nel.org, samuel@...lland.org,
        skhan@...uxfoundation.org, suravee.suthikulpanit@....com,
        thomas.lendacky@....com, tonyhuang.sunplus@...il.com,
        ulf.hansson@...aro.org, vaishnav.a@...com,
        walker.chen@...rfivetech.com, will@...nel.org, zhuyinbo@...ngson.cn
Subject: Re: [PATCH v14 6/8] arm64: dts: Add AMD Pensando Elba SoC support

Hi Brad,

On Wed, May 31, 2023 at 12:04 AM Brad Larson <blarson@....com> wrote:
> On Wed, May 24, 2023 at 13:52 Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Tue, May 23, 2023 at 9:30â€¯PM Brad Larson <blarson@....com> wrote:
> >> On 5/16/23 09:54, Michal Simek wrote:
> >> > On 5/15/23 20:16, Brad Larson wrote:
> >> >> + */
> >> >> +
> >> >> +/ {
> >> >> +    cpus {
> >> >> +            #address-cells = <2>;
> >> >> +            #size-cells = <0>;
> >> >> +
> >> >> +            cpu-map {
> >> >> +                    cluster0 {
> >> >> +                            core0 { cpu = <&cpu0>; };
> >> >> +                            core1 { cpu = <&cpu1>; };
> >> >> +                            core2 { cpu = <&cpu2>; };
> >> >> +                            core3 { cpu = <&cpu3>; };
> >> >> +                    };
> >> >> +
> >> >> +                    cluster1 {
> >> >> +                            core0 { cpu = <&cpu4>; };
> >> >> +                            core1 { cpu = <&cpu5>; };
> >> >> +                            core2 { cpu = <&cpu6>; };
> >> >> +                            core3 { cpu = <&cpu7>; };
> >> >> +                    };
> >> >> +
> >> >> +                    cluster2 {
> >> >> +                            core0 { cpu = <&cpu8>; };
> >> >> +                            core1 { cpu = <&cpu9>; };
> >> >> +                            core2 { cpu = <&cpu10>; };
> >> >> +                            core3 { cpu = <&cpu11>; };
> >> >> +                    };
> >> >> +
> >> >> +                    cluster3 {
> >> >> +                            core0 { cpu = <&cpu12>; };
> >> >> +                            core1 { cpu = <&cpu13>; };
> >> >> +                            core2 { cpu = <&cpu14>; };
> >> >> +                            core3 { cpu = <&cpu15>; };
> >> >> +                    };
> >> >> +            };
> >> >> +
> >> >> +            /* CLUSTER 0 */
> >> >> +            cpu0: cpu@0 {
> >> >> +                    device_type = "cpu";
> >> >> +                    compatible = "arm,cortex-a72";
> >> >> +                    reg = <0 0x0>;
> >> >
> >> > Do you really need 2/0 split here. The first cell is 0 anyway.
> >>
> >> Yes following 64-bit system definition
> >
> > You mean for the 64-bit main address space?
> > The CPU address space under /cpus is unrelated.
>
> Yes, the reg prop for this node is CPU/threads per dt spec.  Checked the history and
> the Elba dt was derived from socionext for these nodes and this is how those device
> trees are configured along with over a dozen other devices.  I changed to
> address-cells = <1> and dropped the leading zero from all cpu* reg<> and booting
> the system I'm observing no change.  Looking in drivers/of I'm not seeing where
> cpu*/reg is read and used, any recommendation?

drivers/of/cpu.c

Looks like there are lots of DTS files that use #address-cells = <2> for
CPU nodes :-(

    git grep -w -A1 cpus -- "*dts*" | grep address-cells | grep "<2>"

I would use <1> is the first cell is always zero...

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