linux-kernel - Re: [PATCH 3/3] arm64: Use include/asm-generic/io.h

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Message-Id: <201407101514.16530.arnd@arndb.de>
Date:	Thu, 10 Jul 2014 15:14:16 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] arm64: Use include/asm-generic/io.h

On Thursday 10 July 2014, Catalin Marinas wrote:
> > @@ -235,8 +155,7 @@ extern void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size);
> >  #define ioremap_wc(addr, size)               __ioremap((addr), (size), __pgprot(PROT_NORMAL_NC))
> >  #define iounmap                              __iounmap
> >  
> > -#define ARCH_HAS_IOREMAP_WC
> > -#include <asm-generic/iomap.h>
> > +#include <asm-generic/io.h>
> 
> We don't currently have PCIe support in mainline for arm64 but what I
> had in mind with the generic iomap is that functions like ioread32_rep
> first check whether the address is an IO address or a memory one and
> calls the insl or mmio_insl accordingly. With your generic
> implementation, this check disappears.
> 
> The question is whether this functionality would still be needed.

I think it's much better not to have that check on architectures that have a memory
mapped I/O space like arm64. The main advantage is that ioread32() is just a trivial
alias for readl(). The only reason for needing generic_iomap is architectures that
do something very different for I/O ports.

	Arnd
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