linux-kernel - Re: [PATCH 1/3] radeonfb: Fix 64 bits resources on 32 bits archs

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Date:	Tue, 22 Apr 2008 17:55:00 +0200
From:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	linux-fbdev-devel@...ts.sourceforge.net, linuxppc-dev@...abs.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, adaplas@...il.com,
	Hollis Blanchard <hollisb@...ibm.com>,
	Wolfgang Denk <wd@...x.de>, Detlev Zundel <dzu@...x.de>
Subject: Re: [PATCH 1/3] radeonfb: Fix 64 bits resources on 32 bits archs

Benjamin Herrenschmidt wrote:
> This fixes radeonfb to not truncate 64 bits resources on 32 bits
> platforms. Unfortunately, there are still issues with addresses
> returned to userspace via struct fb_fix_screeninfo. This will
> have to be dealt with separately.

Thanks for this patch Benjamin, I use it together with what we have discussed in the "pci issue - wrong detection of pci ressources" thread.
Unfortunately I now hit exactly that issue with fb_fix_screeninfo you describe.

For everyone the fb_fix_screeninfo has two "unsigned long" vars that need to strore a IO address.
This fails in my case with a 32bit powerpc system (=sizeof(long)=4) which has paddr >4Gb and actually it should affect any 32bit platform with paddr>4Gb.
You see it e.g. when you try to initialize X11, the x11 radeon driver issues a FBIOGET_FSCREENINFO ioctl and because our address is >4Gb it get's clobbered by that unsigned long in the fb_fix_screeninfo structure (the value comes from a resource_size_t variable which has the correct 64bit).

struct fb_fix_screeninfo {
        char id[16];                    /* identification string eg "TT Builtin" */
        unsigned long smem_start;     /* Start of frame buffer mem */
[...]
        unsigned long mmio_start;     /* Start of Memory Mapped I/O   */
[...]

I tried the stupid solution to just change the fb_fix_screeninfo structure to resource_size_t, but that changes the size ioctl transports and would require awareness in the userspace applications using that ioctl.
The X11 & Framebuffer driver work on 64bit systems, so I think it's just an issue of not cutting that data down to 32bit when transporting it (has anyone already checked the x11 drivers, I hope they don't use unsigned long too).

I wanted to ask if there are any known workarounds atm that would allow me to use my X11 for now?

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
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