linux-kernel - Re: [PATCH] NTB: ntb_perf: fix cast to restricted _

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Date:   Fri, 19 Jan 2018 21:42:17 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     jdmason@...zu.us, Dave Jiang <dave.jiang@...el.com>,
        Allen.Hubbe@...il.com, "Hook, Gary" <gary.hook@....com>,
        Sergey.Semin@...latforms.ru, linux-ntb@...glegroups.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NTB: ntb_perf: fix cast to restricted __le32

On Fri, Jan 19, 2018 at 6:30 PM, Serge Semin <fancer.lancer@...il.com> wrote:
> Sparse is whining about the u32 and __le32 mixed usage in the
> driver.
>
> drivers/ntb/test/ntb_perf.c:288:21: warning: cast to restricted __le32
> drivers/ntb/test/ntb_perf.c:295:37: warning: incorrect type in argument 4 (different base types)
> drivers/ntb/test/ntb_perf.c:295:37:    expected unsigned int [unsigned] [usertype] val
> drivers/ntb/test/ntb_perf.c:295:37:    got restricted __le32 [usertype] <noident>
> ...
>
> The NTB API can't be changed so ntb_spad_*() methods
> would return either pure __le32 or __be32, since the scratchpad
> data can have arbitrary endianness in general. In this case we
> need to forcibly cast all the u32 to be __le32 and vise-versa
> where it's supposed to be in accordance with the driver logic.
>

There's got to be a better way to do this than sprinkling lots of __force
typecasts throughout the code.

It looks like all those casts are about
ntb_peer_spad_read()/ntb_peer_msg_write() calls, so why not change
those function prototypes to work on __le32 types?

There should also be some form of documentation regarding why you
need to swap the data twice, since all the ntb drivers later end up
doing another cpu_to_le32() on the little-endian data.

       Arnd