Re: Problem with framebuffer mmap on platforms with large addressing

On Sun, Mar 18, 2012 at 4:46 AM, Benjamin Herrenschmidt
[off-list ref] wrote:

On Sat, 2012-03-17 at 20:04 +0400, Dmitry Eremin-Solenikov wrote:

quoted

Hello,

I'm trying to make framebuffer to work on PPC460EX board (canyonlands).

The peculiarity of this platform is the fact that it has
sizeof(unsigned long) = 4,
but physical address on it is 36 bits width. It is a common to various pieces
of the code to expect that unsigned long variable is able to contain physical
address. Most of those places are easy to fix.

Yes. In fact, Tony (CC) has some patches to fix a lot of the DRM
infrastructure (we have radeon KMS working on a similar platform).

That is interesting! Are those patches published or otherwise available
somewhere? We are also very interested in enabling Canyonlands
with Radeon KMS!

quoted

The problem I'm stuck with is a fb_mmap() code. To find a right memory to map
it uses information from struct fb_fix_screeninfo provided by the driver.
This structure uses two unsigned long fields to hold physical addresses
(smem_start and mmio_start). It would be easy to change that structure
to use phys_addr_t instead of unsigned long, but this structure is a part
of userspace ABI. It is returned to userspace on FBIOGET_FSCREENINFO ioctl.
And now I'm stuck with it.

It's an old problem, which I think we described a while back on the
list. Back then the conclusion was to make a new version with a proper
__u64, a new ioctl to access is, and a "compatible" ioctl that blanks
the address fields (or fails) if they contain a value >32-bit.

We just never got to actually implement it.

I see. I will try to prepare patches.

In fact, we could make the new structure such that it doesn't break
userspace compatibility with 64-bit architectures at all, ie, the "new"
and "compat" ioctl could remain entirely equivalent on 64-bit.

I remember stuff about compat_ioctl, but I have never used/implemented
that. Are there any details of requirements for the structures being passed?

-- 
With best wishes
Dmitry