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Message-ID: <YQSsiacvJHFKk3Cj@boqun-archlinux>
Date: Sat, 31 Jul 2021 09:51:05 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: 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 10:24:53PM +0200, Arnd Bergmann wrote:
> 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.
>
Agreed. I wasn't planning to propose this kind of checks for C code.
Just want to understand better on the alignment requirement of these
APIs. Thanks ;-)
Regards,
Boqun
> Arnd
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