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Message-ID: <77e747de-c7d6-314d-e0b0-58852d463326@vivier.eu>
Date:   Sun, 16 Jan 2022 12:54:04 +0100
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Subject: Re: [PATCH v8 3/4] clocksource/drivers: Add a goldfish-timer
 clocksource
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To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        John Stultz <john.stultz@linaro.org>,
        linux-rtc@vger.kernel.org, Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        linux-m68k <linux-m68k@lists.linux-m68k.org>
References: <20220115193245.3777833-1-laurent@vivier.eu>
 <20220115193245.3777833-4-laurent@vivier.eu>
 <CAK8P3a13g_o4mTsOO-4b=WU6TGRHubY7HCt1x1FdXpVmjy6-Sg@mail.gmail.com>
From:   Laurent Vivier <laurent@vivier.eu>
In-Reply-To: <CAK8P3a13g_o4mTsOO-4b=WU6TGRHubY7HCt1x1FdXpVmjy6-Sg@mail.gmail.com>
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Le 16/01/2022 à 11:44, Arnd Bergmann a écrit :
> On Sat, Jan 15, 2022 at 8:32 PM Laurent Vivier <laurent@vivier.eu> wrote:
> 
>> +
>> +/* goldfish endianness depends on CPU endianness */
>> +#ifdef CONFIG_CPU_BIG_ENDIAN
>> +#define goldfish_ioread32 ioread32be
>> +#define goldfish_iowrite32 iowrite32be
>> +#else
>> +#define goldfish_ioread32 ioread32
>> +#define goldfish_iowrite32 iowrite32
>> +#endif
> 
> This is not what I meant here, as you are breaking big-endian support
> for all other
> architectures in the process.
> 
> On architectures that support both big-endian and little-endian kernels, devices
> (including emulated ones) can't know which type of kernel you are running, so
> this has to be fixed by architecture. Ideally this macro should be in
> an architecture
> specific header file, but you can also just make this a check for m68k and  hope
> that qemu doesn't duplicate this bug on architectures that gain support for this
> driver in the future.

Virtio has exactly the same problem in the past (prio to v1.0), and it uses __LITTLE_ENDIAN in 
virtio_legacy_is_little_endian() to know the endianness of the device.

So the code can become:

#ifdef __LITTLE_ENDIAN
#define goldfish_ioread32 ioread32
#define goldfish_iowrite32 iowrite32
#else
#define goldfish_ioread32 ioread32be
#define goldfish_iowrite32 iowrite32be
#endif

What do you prefer: CONFIG_M68K or __LITTLE_ENDIAN?

Thanks,
Laurent