Kernel almost hangs when CONFIG_DRM_RADEON=y

[Kyle Moffett]

2011/8/27 Michel Dänzer <michel at daenzer.net>:
> On Sam, 2011-08-27 at 00:20 -0400, Pavel Ivanov wrote:
>> I observe very strange behavior dependent on value of
>> CONFIG_DRM_RADEON parameter. When it's set to m everything works very
>> good, no problem. When I set it to y I see kernel hang during boot. Or
>> I should better say it "almost hangs" because during last boot attempt
>> I accidentally waited a little bit longer and saw that after more than
>> a minute waiting system continued to boot. Dmesg after "hang" shows
>> these messages:
>>
>> [    8.542639] [drm] Loading CEDAR Microcode
>> [   69.161605] r600_cp: Failed to load firmware "radeon/CEDAR_pfp.bin"
>> [   69.161670] [drm:evergreen_startup] *ERROR* Failed to load firmware!
>>
>> While during normal boot
>>
>> [    9.898870] [drm] Loading CEDAR Microcode
>> [    9.908425] radeon 0000:05:00.0: WB enabled
>
> With CONFIG_DRM_RADEON=y, the microcode is needed before it can be
> loaded from userspace, so it needs to be built into the kernel as well.

Linus has gotten pissed previously about drivers that do this.

I actually recall a patch previously that made request_firmware() fail instantly
before userspace is loaded, which would get rid of the hang, but presumably
not actually make the driver work when built-in.

The solution is to allow the driver to "attach" to the device but if
the firmware is
not available at that time then retrying the request_firmware() later, ideally
triggered from some userspace action.

Cheers,
Kyle Moffett