linux-kernel - Re: [PATCH][v2] uio: Support 36-bit physical addresses on 32-bit systems

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Message-ID: <CAOZdJXWd_u_EWXNhh3-t258+Y8mx=JuJhU93CeZfaocPZvhOFA@mail.gmail.com>
Date:	Thu, 13 Oct 2011 14:37:17 +0000
From:	Tabi Timur-B04825 <B04825@...escale.com>
To:	Kumar Gala <galak@...nel.crashing.org>
CC:	"hjk@...sjkoch.de" <hjk@...sjkoch.de>,
	"linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
	"gregkh@...e.de" <gregkh@...e.de>,
	Jiang Kai-B18973 <B18973@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][v2] uio: Support 36-bit physical addresses on 32-bit
 systems

On Wed, Oct 12, 2011 at 3:57 PM, Kumar Gala <galak@...nel.crashing.org> wrote:
> From: Kai Jiang <Kai.Jiang@...escale.com>
>
> To support >32-bit physical addresses for UIO_MEM_PHYS type we need to
> extend the width of 'addr' in struct uio_mem.  Numerous platforms like
> embedded PPC, ARM, and X86 have support for systems with larger physical
> address than logical.
>
> Since 'addr' may contain a physical, logical, or virtual address the
> easiest solution is to just change the type to 'unsigned long long'
> regardless of which type is utilized.

You forgot to update this description.

>  struct uio_mem {
>        const char              *name;
> -       unsigned long           addr;
> +       phys_addr_t             addr;

Please add a comment here saying:

1) That 'addr' can be a virtual or physical address
2) That the kernel guarantees that sizeof(phys_addr_t) >= sizeof(void
*), so it's safe to use phys_addr_t for a virtual pointer.

-- 
Timur Tabi
Linux kernel developer at Freescale
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