linux-kernel - Re: [Question] Alignment requirement for readX() and writeX()

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Date:   Fri, 30 Jul 2021 22:24:53 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Gary Guo <gary@...yguo.net>, Hector Martin <marcan@...can.st>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [Question] Alignment requirement for readX() and writeX()

On Fri, Jul 30, 2021 at 7:31 PM Boqun Feng <boqun.feng@...il.com> wrote:
> On Fri, Jul 30, 2021 at 06:58:30PM +0200, Arnd Bergmann wrote:
>
> If we want to check, I'd expect we do the checks inside
> readX()/writeX(), for example, readl() could be implemented as:
>
>         #define readl(c)                                        \
>         ({                                                      \
>                 u32 __v;                                        \
>                                                                 \
>                 /* alignment checking */                        \
>                 BUG_ON(c & (sizeof(__v) - 1));                  \
>                 __v = readl_relaxed(c);                         \
>                 __iormb(__v);                                   \
>                 __v;                                            \
>         })
>
> It's a runtime check, so if anyone hates it I can understand ;-)

Right, I really don't think that adds any value, this just replaces one
oops message with a more different oops message, while adding
some overhead.

        Arnd