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

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Message-Id: <20160828.234635.224236136235372450.davem@davemloft.net>
Date:   Sun, 28 Aug 2016 23:46:35 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     rmk+kernel@...linux.org.uk
Cc:     linux-arm-kernel@...ts.infradead.org, nico@...xnic.net,
        robert.jarzmik@...e.fr, arnd@...db.de, daniel@...que.org,
        haojian.zhuang@...il.com, realmz6@...il.com,
        adi-buildroot-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH v2] net: smc91x: fix SMC accesses

From: Russell King <rmk+kernel@...linux.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@...linux.org.uk>

Applied and queued up for -stable, thanks Russell.