linux-kernel - Re: [PATCH v1 02/10] powerpc/mm: rework io-workaround invocation.

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Message-ID: <20190814053843.GB27497@infradead.org>
Date:   Tue, 13 Aug 2019 22:38:43 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 02/10] powerpc/mm: rework io-workaround invocation.

On Tue, Aug 13, 2019 at 08:11:34PM +0000, Christophe Leroy wrote:
> ppc_md.ioremap() is only used for I/O workaround on CELL platform,
> so indirect function call can be avoided.
> 
> This patch reworks the io-workaround and ioremap() functions to
> use static keys for the activation of io-workaround.
> 
> When CONFIG_PPC_IO_WORKAROUNDS or CONFIG_PPC_INDIRECT_MMIO are not
> selected, the I/O workaround ioremap() voids and the static key is
> not used at all.

Why bother with the complex static key?  ioremap isn't exactly a fast
path.  Just make it a normal branch if enabled, with the option to
compile it out entirely as in your patch.