linux-kernel - Re: [PATCH v2 13/31] arm64: Device specific operations

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Message-ID: <20120815003355.GF19607@quad.lixom.net>
Date:	Tue, 14 Aug 2012 17:33:55 -0700
From:	Olof Johansson <olof@...om.net>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v2 13/31] arm64: Device specific operations

On Tue, Aug 14, 2012 at 06:52:14PM +0100, Catalin Marinas wrote:
> This patch adds several definitions for device communication, including
> I/O accessors and ioremap(). The __raw_* accessors are implemented as
> inline asm to avoid compiler generation of post-indexed accesses (less
> efficient to emulate in a virtualised environment).
> 
> Signed-off-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> ---
>  arch/arm64/include/asm/device.h |   26 ++++
>  arch/arm64/include/asm/fb.h     |   34 +++++
>  arch/arm64/include/asm/io.h     |  263 +++++++++++++++++++++++++++++++++++++++
>  arch/arm64/kernel/io.c          |   64 ++++++++++
>  arch/arm64/mm/ioremap.c         |   84 +++++++++++++
>  5 files changed, 471 insertions(+), 0 deletions(-)
>  create mode 100644 arch/arm64/include/asm/device.h
>  create mode 100644 arch/arm64/include/asm/fb.h
>  create mode 100644 arch/arm64/include/asm/io.h
>  create mode 100644 arch/arm64/kernel/io.c
>  create mode 100644 arch/arm64/mm/ioremap.c
> 
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> new file mode 100644
> index 0000000..48fa83f
> --- /dev/null
> +++ b/arch/arm64/include/asm/io.h

[...]

> +/*
> + *  I/O port access primitives.
> + */
> +#define IO_SPACE_LIMIT		0xffff
> +
> +/*
> + * We currently don't have any platform with PCI support, so just leave this
> + * defined to 0 until needed.
> + */
> +#define PCI_IOBASE		((void __iomem *)0)

You could just leave out the PCI / I/O code alltogether instead.

> diff --git a/arch/arm64/kernel/io.c b/arch/arm64/kernel/io.c
> new file mode 100644
> index 0000000..7d37ead
> --- /dev/null
> +++ b/arch/arm64/kernel/io.c
> @@ -0,0 +1,64 @@
> +/*
> + * Based on arch/arm/kernel/io.c
> + *
> + * Copyright (C) 2012 ARM Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/types.h>
> +#include <linux/io.h>
> +
> +/*
> + * Copy data from IO memory space to "real" memory space.
> + */
> +void __memcpy_fromio(void *to, const volatile void __iomem *from, size_t count)
> +{
> +	unsigned char *t = to;
> +	while (count) {
> +		count--;
> +		*t = readb(from);
> +		t++;
> +		from++;
> +	}
> +}
> +EXPORT_SYMBOL(__memcpy_fromio);
> +
> +/*
> + * Copy data from "real" memory space to IO memory space.
> + */
> +void __memcpy_toio(volatile void __iomem *to, const void *from, size_t count)
> +{
> +	const unsigned char *f = from;
> +	while (count) {
> +		count--;
> +		writeb(*f, to);
> +		f++;
> +		to++;
> +	}
> +}
> +EXPORT_SYMBOL(__memcpy_toio);
> +
> +/*
> + * "memset" on IO memory space.
> + */
> +void __memset_io(volatile void __iomem *dst, int c, size_t count)
> +{
> +	while (count) {
> +		count--;
> +		writeb(c, dst);
> +		dst++;
> +	}
> +}
> +EXPORT_SYMBOL(__memset_io);

Doing all of the above a byte at a time is horribly inefficient. Feel
free to borrow the implementations from arch/powerpc/kernel/io.c instead
of from ARM.


-Olof
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