linux-kernel - Re: [V2, 2/6] tty: serial: lpuart: add little endian 32 bit register support

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Message-ID: <CAHp75VdL=rGHuupGmgmAVonEQgpyPRgoMQrZK0yQiaM=1Vac-g@mail.gmail.com>
Date:   Wed, 17 May 2017 12:55:59 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dong Aisheng <dongas86@...il.com>
Cc:     Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Dong Aisheng <aisheng.dong@....com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        fugang.duan@....com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        yangbo.lu@....com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stefan Agner <stefan@...er.ch>, Mingkai.Hu@....com,
        Jiri Slaby <jslaby@...e.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [V2, 2/6] tty: serial: lpuart: add little endian 32 bit register support

On Wed, May 17, 2017 at 8:43 AM, Dong Aisheng <dongas86@...il.com> wrote:
> On Wed, May 17, 2017 at 08:37:41AM +0300, Nikita Yushchenko wrote:
>>
>>
>> 17.05.2017 06:39, Dong Aisheng wrote:
>> > On Tue, May 16, 2017 at 02:15:08PM +0300, Nikita Yushchenko wrote:
>> >>>  static u32 lpuart32_read(void __iomem *addr)
>> >>>  {
>> >>> - return ioread32be(addr);
>> >>> + return lpuart_is_be ? ioread32be(addr) : readl(addr);
>> >>>  }
>> >>>
>> >>>  static void lpuart32_write(u32 val, void __iomem *addr)
>> >>>  {
>> >>> - iowrite32be(val, addr);
>> >>> + if (lpuart_is_be)
>> >>> +         iowrite32be(val, addr);
>> >>> + else
>> >>> +         writel(val, addr);
>> >>>  }
>> >>
>> >> What if this is ever executed on big endian system?
>> >>
>> >
>> > Sorry, not catching the point...
>> >
>> > What issues will meet?
>>
>> Isn't writel() in host endian?
>
> On big endian systems, it is supposed to run iowrite32be.

It looks like you substituting *bus* side with CPU *side* of communication.

If you are talking about CPU side
__raw_readl() / __raw_writel() will do the trick.

-- 
With Best Regards,
Andy Shevchenko