linux-kernel - Re: [PATCH v10 2/5] rtc: goldfish: introduce goldfish_ioread32()/goldfish

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Message-ID: <CAMuHMdXSFU4N+FLYkCLJCJcWJ74g=8Vr23Rx0cka-kDTBs6Z4Q@mail.gmail.com>
Date:   Wed, 19 Jan 2022 09:21:46 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Laurent Vivier <laurent@...ier.eu>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        John Stultz <john.stultz@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, linux-rtc@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH v10 2/5] rtc: goldfish: introduce goldfish_ioread32()/goldfish_iowrite32()

Hi Laurent,

On Wed, Jan 19, 2022 at 1:05 AM Laurent Vivier <laurent@...ier.eu> wrote:
> The goldfish device always uses the same endianness as the architecture
> using it:
> https://android.googlesource.com/platform/external/qemu/+/refs/heads/emu-master-dev/hw/timer/goldfish_timer.c#177
>
> On a big-endian machine, the device is also big-endian, on a
> little-endian machine the device is little-endian.
>
> So we need to use the right accessor to read/write values to the goldfish
> registers: ioread32()/iowrite32() on a little-endian machine,
> ioread32be()/iowrite32be() on a big-endian machine.
>
> This patch introduces goldfish_ioread32()/goldfish_iowrite32() to allow
> architectures to define them accordlingly to their endianness.
>
> We define them by default in asm-generic/io.h to access the device using
> little-endian access as it is the current use, but we will be able to define
> big-endian version when new architectures will use them.
>
> Signed-off-by: Laurent Vivier <laurent@...ier.eu>

Thanks for your patch!

> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -906,6 +906,13 @@ static inline void iowrite64_rep(volatile void __iomem *addr,
>  #endif /* CONFIG_64BIT */
>  #endif /* CONFIG_GENERIC_IOMAP */
>
> +#ifndef goldfish_ioread32
> +#define goldfish_ioread32 ioread32
> +#endif
> +#ifndef goldfish_iowrite32
> +#define goldfish_iowrite32 iowrite32
> +#endif
> +
>  #ifdef __KERNEL__

I've just discovered include/linux/goldfish.h, which already has gf_*()
accessors for 64-bit, so it'd make sense to move the above there,
and adjust the names.

Arnd: note that the existing ones do use __raw_writel().

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