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

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Message-ID: <653402b90610300932r3c96445bxb8e5d34f8f768ec4@mail.gmail.com>
Date:	Mon, 30 Oct 2006 18:32:37 +0100
From:	"Miguel Ojeda" <maxextreme@...il.com>
To:	"Paulo Marques" <pmarques@...popie.com>
Cc:	Franck <vagabon.xyz@...il.com>, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.19-rc1 full] drivers: add LCD support

On 10/30/06, Paulo Marques <pmarques@...popie.com> wrote:
>
> No, this is not the sequence I thought of at all. I don't remember the
> exact API functions you need to call (I have to read LDD3 again ;), but
> if the hardware supports it, there must be a way. The plan is something
> like:
>
>   - at mmap time you return a pointer to something that is not actually
> mapped, and do nothing else
>
>   - when userspace actually writes to that area, you get a page fault,
> and nopage is called. At this point you map the page, and set the dirty
> state. All other writes from userspace until the timer completes are
> done without faulting.
>
>   - when the timer completes, you unmap the page so that the next access
> will generate a fault again
>
> As I said, I don't remember the exact details, but this should be doable.
>

Yes, I get the idea, you mean to "unmap" the page but don't remove the
vma so a page fault is raised and nopage() op must be called again.
May it decrease performance? (Linux /you must take care of a page
fault calling nopage() each time you write/refresh the LCD, then
actually use it).

      Miguel Ojeda
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