linux-kernel - Re: [PATCH 2.6.19-rc1 full] drivers: add LCD support

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Message-ID: <653402b90610300535n6d26be8fr29df1c491f033533@mail.gmail.com>
Date:	Mon, 30 Oct 2006 14:35:01 +0100
From:	"Miguel Ojeda" <maxextreme@...il.com>
To:	Franck <vagabon.xyz@...il.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.19-rc1 full] drivers: add LCD support

On 10/30/06, Franck Bui-Huu <vagabon.xyz@...il.com> wrote:
> Miguel Ojeda wrote:
> >
> > Sorry, I meant: You can't mmap a RAM address using functions like the
> > usual remap_pfn_range (as such functions doesn't like physical RAM
> > addresses, they want I/O ports for example, like 0x378). So, you can't
> > use smem_start. You need to code your own mmap & nopage function. (It
> > is explained in LDD3 very well).
> >
>
> well I must admit that I don't understand why... I suppose you refered
> to that section in ldd3:
>
>         An interesting limitation of remap_pfn_range is that it gives
>         access only to reserved pages and physical addresses above the
>         top of physical memory.
>
> I take a quick look at the implementation of remap_pfn_range() and
> there's no such limitation I can see (fortunately).
>
>                 Franck
>

Read further ;-)

      "Therefore, remap_pfn_range won't allow you to remap
conventional addresses, which include the ones you obtain by calling
get_free_pages"

Because of such limitation, they teach you to remap RAM in other ways.
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