linux-kernel - Re: [PATCH v2 09/16] reset: starfive-jh7100: Add StarFive JH7100 reset driver

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Message-ID: <CAHp75VfwmSfeUPvUXT3TTf0ZYGMfBZ0qaPoB0_SCzyR=Fb_Emw@mail.gmail.com>
Date:   Fri, 22 Oct 2021 18:24:20 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Emil Renner Berthing <kernel@...il.dk>
Cc:     linux-riscv <linux-riscv@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Drew Fustini <drew@...gleboard.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michael Zhu <michael.zhu@...rfivetech.com>,
        Fu Wei <tekkamanninja@...il.com>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Matteo Croce <mcroce@...rosoft.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 09/16] reset: starfive-jh7100: Add StarFive JH7100
 reset driver

On Fri, Oct 22, 2021 at 5:56 PM Emil Renner Berthing <kernel@...il.dk> wrote:
> On Fri, 22 Oct 2021 at 16:50, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > On Fri, Oct 22, 2021 at 5:25 PM Emil Renner Berthing <kernel@...il.dk> wrote:
> > > On Fri, 22 Oct 2021 at 15:39, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > > > On Fri, Oct 22, 2021 at 4:35 PM Emil Renner Berthing <kernel@...il.dk> wrote:
> > > > > On Fri, 22 Oct 2021 at 14:56, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > > > > > On Thu, Oct 21, 2021 at 8:43 PM Emil Renner Berthing <kernel@...il.dk> wrote:

...

> > > > > > Why all these ugly % 32 against constants?
> > > > >
> > > > > Because the JH7100_RST_ values goes higher than 31. There is a
> > > > > BIT_MASK macro, but that does % BITS_PER_LONG and this is a 64bit
> > > > > machine.
> > > >
> > > > And? It's exactly what you have to use!
> > >
> > > So you want me to use an unsigned long array or DECLARE_BITMAP and
> > > juggle two different index and bit offsets?
> >
> > What are the offsets of those status registers?
> > AFAICS they are sequential 4 32-bit registers.
>
> That's right, but we're on a 64bit machine, so DECLARE_BITMAP will
> give us an unsigned long array that doesn't match that.

I didn't get it, sorry.
You will have a bitmap array which you will split to 32-bit values.
What you will probably need is to move  xgpio_get_value32() and void
xgpio_set_value32() to the one of bitmap related headers (look for
bitmap_get_value8() and friends).

> > So bitmap is exactly what is suitable here, you are right!
> > See gpio-xilinx and gpio-pca953x on how to use bitmaps in the GPIO drivers.
>
> None of them has a pre-initialized const DECLARE_BITMAP, so they don't
> have to deal with the 4 vs. 2 commas problem.

I believe it's well possible to refactor this to look much better with
bitmaps (as it represents the hardware very well).

> > > Also is there a macro for handling that we'd then need 4 commas on
> > > 32bit COMPILE_TEST and 2 commas on 64bit?
> > > If you have some other way in mind you'll have to be a lot more explicit again.
> > >
> > > The point of the jh7100_reset_asserted array is that it exactly
> > > mirrors the values of the status registers when the lines are
> > > asserted. Maybe writing it like this would be more explicit:
> > >
> > > static const u32 jh7100_reset_asserted[4] = {
> > >         /* STATUS0 register */
> > >         BIT(JH7100_RST_U74 % 32) |
> > >         BIT(JH7100_RST_VP6_DRESET % 32) |
> > >         BIT(JH7100_RST_VP6_BRESET % 32),
> > >         /* STATUS1 register */
> > >         BIT(JH7100_RST_HIFI4_DRESET % 32) |
> > >         BIT(JH7100_RST_HIFI4_BRESET % 32),
> > >         /* STATUS2 register */
> > >         BIT(JH7100_RST_E24 % 32),
> > >         /* STATUS3 register */
> > >         0,
> > > };

-- 
With Best Regards,
Andy Shevchenko