Re: [PATCH v2] net: smc91x: fix SMC accesses

David Miller
2016-08-29T03:46:35Z

From: Russell King <rmk+kernel@armlinux.org.uk>
Date: Sat, 27 Aug 2016 17:33:03 +0100

> Commit b70661c70830 ("net: smc91x: use run-time configuration on all ARM
> machines") broke some ARM platforms through several mistakes. Firstly,
> the access size must correspond to the following rule:
>
> (a) at least one of 16-bit or 8-bit access size must be supported
> (b) 32-bit accesses are optional, and may be enabled in addition to
> the above.
>
> Secondly, it provides no emulation of 16-bit accesses, instead blindly
> making 16-bit accesses even when the platform specifies that only 8-bit
> is supported.
>
> Reorganise smc91x.h so we can make use of the existing 16-bit access
> emulation already provided - if 16-bit accesses are supported, use
> 16-bit accesses directly, otherwise if 8-bit accesses are supported,
> use the provided 16-bit access emulation. If neither, BUG(). This
> exactly reflects the driver behaviour prior to the commit being fixed.
>
> Since the conversion incorrectly cut down the available access sizes on
> several platforms, we also need to go through every platform and fix up
> the overly-restrictive access size: Arnd assumed that if a platform can
> perform 32-bit, 16-bit and 8-bit accesses, then only a 32-bit access
> size needed to be specified - not so, all available access sizes must
> be specified.
>
> This likely fixes some performance regressions in doing this: if a
> platform does not support 8-bit accesses, 8-bit accesses have been
> emulated by performing a 16-bit read-modify-write access.
>
> Tested on the Intel Assabet/Neponset platform, which supports only 8-bit
> accesses, which was broken by the original commit.
>
> Fixes: b70661c70830 ("net: smc91x: use run-time configuration on all ARM machines")
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

Applied and queued up for -stable, thanks Russell.