linux-kernel - Re: [patch 3/6] add pmem driver

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Message-ID: <a55d774e0909141519i752eca3dp7ab848e1c1154530@mail.gmail.com>
Date:	Mon, 14 Sep 2009 15:19:11 -0700
From:	Brian Swetland <swetland@...gle.com>
To:	Daniel Walker <dwalker@...o99.com>
Cc:	Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
	arve@...roid.com, kernel list <linux-kernel@...r.kernel.org>,
	Iliyan Malchev <malchev@...gle.com>,
	Petri Gynther <pgynther@...gle.com>
Subject: Re: [patch 3/6] add pmem driver

On Mon, Sep 14, 2009 at 3:06 PM, Daniel Walker <dwalker@...o99.com> wrote:
> On Mon, 2009-09-14 at 23:58 +0200, Pavel Machek wrote:
>>
>> This adds android pmem driver, one of dependencies of camera driver.
>
> I wouldn't even both with this one .. There's no way it could ever go
> into mainline .. According to the android developers the camera , and
> the frame buffer driver should work without it anyway..

The latest camera driver should work without pmem (or be fixable to do
so -- I forget if that's done yet).

The framebuffer itself does not need pmem, but pmem is used heavily by
the android userspace on dream/magic for hardware compositable
surfaces (since the 2d compositor requires physically contiguous
memory).

Is there a general linux kernel solution for managing large (1-8MB+)
chunks of physically contiguous memory that needs to be shared between
kernel and userspace for media operations?  This is a very common
problem with these SoCs -- the a/v subsystem and/or GPU don't have
scatter/gather or MMU support and as a result we need to carve out
memory for their use and provide some way for userspace to manipulate
it.

Brian
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