linux-kernel - Re: [PATCH] misc: Kconfig: add a new dependency for MARVELL_CN10K

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Message-Id: <83ac6b91-c7f1-4b18-a522-8188d6d1298b@app.fastmail.com>
Date: Tue, 16 Jul 2024 15:51:08 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Nathan Chancellor" <nathan@...nel.org>,
 "Vamsi Attunuru" <vattunuru@...vell.com>
Cc: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc: Kconfig: add a new dependency for MARVELL_CN10K_DPI

On Tue, Jul 16, 2024, at 15:26, Nathan Chancellor wrote:
> On Thu, Jul 11, 2024 at 05:01:15AM -0700, Vamsi Attunuru wrote:
>> 
>
> After this change, ARCH=arm allmodconfig fails with:
>
>   drivers/misc/mrvl_cn10k_dpi.c: In function 'dpi_reg_write':
>   drivers/misc/mrvl_cn10k_dpi.c:190:9: error: implicit declaration of 
> function 'writeq'; did you mean 'writeb'? 
> [-Wimplicit-function-declaration]
>     190 |         writeq(val, dpi->reg_base + offset);
>         |         ^~~~~~
>         |         writeb
>   drivers/misc/mrvl_cn10k_dpi.c: In function 'dpi_reg_read':
>   drivers/misc/mrvl_cn10k_dpi.c:195:16: error: implicit declaration of 
> function 'readq'; did you mean 'readb'? 
> [-Wimplicit-function-declaration]
>     195 |         return readq(dpi->reg_base + offset);
>         |                ^~~~~
>         |                readb
>
> Including one of the io-64-nonatomic headers would resolve this but I am
> not sure which one would be appropriate (or perhaps the dependency
> should be tightened to requiring 64BIT, as some other drivers have
> done).

Right, a dependency on 64BIT makes sense here. The alternative is
to include linux/io-64-nonatomic-hi-lo.h or linux/io-64-nonatomic-lo-hi.h
in order to have a replacement readq/writeq implementation that
works on 32-bit architectures. However, doing this requires
understanding whether what the side-effects of accessing the
64-bit registers are and whether they require writing the upper
or lower half of the register last.

     Arnd