From: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
Guenter Roeck <linux@roeck-us.net>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
dma <dmaengine@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] fsldma: fsl_ioread64*() do not need lower_32_bits()
Date: Sun, 30 Aug 2020 14:11:54 +0200 [thread overview]
Message-ID: <20200830121154.zo54k5ywpdk2rw4m@ltop.local> (raw)
In-Reply-To: <CAHk-=whH0ApHy0evN0q6AwQ+-a5RK56oMkYkkCJtTMnaq4FrNQ@mail.gmail.com>
On Sat, Aug 29, 2020 at 10:29:55AM -0700, Linus Torvalds wrote:
> On Sat, Aug 29, 2020 at 5:46 AM Luc Van Oostenryck
> <luc.vanoostenryck@gmail.com> wrote:
> >
> > But the pointer is already 32-bit, so simply cast the pointer to u32.
>
> Yeah, that code was completely pointless. If the pointer had actually
> been 64-bit, the old code would have warned too.
>
> The odd thing is that the fsl_iowrite64() functions make sense. It's
> only the fsl_ioread64() functions that seem to be written by somebody
> who is really confused.
>
> That said, this patch only humors the confusion. The cast to 'u32' is
> completely pointless. In fact, it seems to be actively wrong, because
> it means that the later "fsl_addr + 1" is done entirely incorrectly -
> it now literally adds "1" to an integer value, while the iowrite()
> functions will add one to a "u32 __iomem *" pointer (so will do
> pointer arithmetic, and add 4).
>
My bad. I had noticed the '+ 1' and so automatically assumed
'OK, pointer arithmetic now' without noticing that the cast was
done only after the addition. Grrr.
FWIW, the version you committed looks much better to me.
-- Luc
next prev parent reply other threads:[~2020-08-30 12:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-28 7:11 [PATCH] kernel.h: Silence sparse warning in lower_32_bits Herbert Xu
2020-08-29 10:51 ` Guenter Roeck
2020-08-29 12:45 ` [PATCH] dmaengine: fsldma: Do not pass pointers to lower_32_bits Herbert Xu
2020-08-29 15:08 ` Guenter Roeck
2020-08-29 12:45 ` [PATCH] fsldma: fsl_ioread64*() do not need lower_32_bits() Luc Van Oostenryck
2020-08-29 17:29 ` Linus Torvalds
2020-08-29 20:40 ` Guenter Roeck
2020-08-29 21:20 ` Linus Torvalds
2020-08-31 1:54 ` Michael Ellerman
2020-08-31 6:39 ` Vinod Koul
2020-08-31 14:25 ` Leo Li
2020-08-30 12:11 ` Luc Van Oostenryck [this message]
2020-08-29 15:05 Guenter Roeck
2020-08-29 15:58 ` Christophe Leroy
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