linux-kernel - Re: [PATCH v2 1/1] fs: debugfs: fix build error at powerpc platform

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Message-Id: <32cd13af-21fa-45bf-9250-b5f3ca132b9b@app.fastmail.com>
Date:   Mon, 02 Oct 2023 20:14:47 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Frank Li" <Frank.Li@....com>, "Baoquan He" <bhe@...hat.com>
Cc:     dmaengine@...r.kernel.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        imx@...ts.linux.dev, linux-kernel@...r.kernel.org,
        "kernel test robot" <lkp@...el.com>, oe-kbuild-all@...ts.linux.dev,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        "Vinod Koul" <vkoul@...nel.org>
Subject: Re: [PATCH v2 1/1] fs: debugfs: fix build error at powerpc platform

On Mon, Oct 2, 2023, at 16:57, Frank Li wrote:
> ld: fs/debugfs/file.o: in function `debugfs_print_regs':
>    file.c:(.text+0x95a): undefined reference to `ioread64be'
>>> ld: file.c:(.text+0x9dd): undefined reference to `ioread64'
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: 
> https://lore.kernel.org/oe-kbuild-all/202309291322.3pZiyosI-lkp@intel.com/
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---

I still think this is wrong, for the reasons I explained in
https://lore.kernel.org/all/b795ed61-0174-487f-a263-8431e7c76af5@app.fastmail.com/

The part that I had missed earlier is how this is
related to GENERIC_IOMAP, since on those architectures,
the ioread helpers are not just fixed-endian MMIO accessors
like readl and readq but also multiplex to the PIO functions
(inb/inw/inl) that do not have a 64-bit version because x86
and PCI both only define those up to 32 bit width.

The best workaround is probably to use readq() instead of
ioread64(), or swab64(readl()) instead of ioread64_be().

This should work on all 64-bit architectures, plus any 32-bit
one that defines readq(), so you can just use an 'ifdef readq'
around the call.

     Arnd