Re: [PATCH v3] Fix loading of module radeonfb on PowerMac

Hi Bartlomiej,

On Wed, Jan 3, 2018 at 4:23 PM, Lennart Sorensen
[off-list ref] wrote:

On Wed, Jan 03, 2018 at 03:47:35PM +0100, Bartlomiej Zolnierkiewicz wrote:

quoted

On Thursday, December 21, 2017 11:07:56 PM Mathieu Malaterre wrote:

quoted

When the linux kernel is build with (typical kernel ship with Debian
installer):

CONFIG_FB_OF=y
CONFIG_VT_HW_CONSOLE_BINDING=y
CONFIG_FB_RADEON=m

The offb driver takes precedence over module radeonfb. It is then
impossible to load the module, error reported is:

[   96.551486] radeonfb 0000:00:10.0: enabling device (0006 -> 0007)
[   96.551526] radeonfb 0000:00:10.0: BAR 0: can't reserve [mem 0x98000000-0x9fffffff pref]
[   96.551531] radeonfb (0000:00:10.0): cannot request region 0.
[   96.551545] radeonfb: probe of 0000:00:10.0 failed with error -16

This patch reproduce the behavior of the module radeon, so as to make it
possible to load radeonfb when offb is first loaded.

It should be noticed that `offb_destroy` is never called which explain the
need to skip error detection on the radeon side.

This still needs to be explained more, from my last mail:

"The last put_fb_info() on fb_info should call ->fb_destroy
(offb_destroy in our case) and remove_conflicting_framebuffers()
is calling put_fb_info() so there is some extra reference on
fb_info somewhere preventing it from going away.

Please look into fixing this."

My impression of that problem is that the offb driver is in use because
it is running the console, and until the radeonfb driver is loaded and
ready to take over, you can't stop using the offb driver, but you can't
currently load the radeonfb because offb is holding resources it wants.

Maybe I have misunderstood what the code is doing, but that seems to be
the problem.

On an x86 PC you could drop one fb and go to text mode then start another
fb driver.  PPC doesn't have that option since there is no text mode.

For reference my patch was inspired by commit:

https://github.com/torvalds/linux/commit/a56f7428d7534f162fbb089c5c79012bf38a7c29

While doing the search, I discover my patch is incorrect, I need to
integrate change from:

https://github.com/torvalds/linux/commit/44adece57e2604cec8527a499b48e4d584ab53b8#diff-767fb253c0135686111755f394d64199

So I'll submit a v4 anyway.

Thanks all,