Re: Switching fb backend back to default

On 3/17/19 2:50 PM, Johannes Lundberg wrote:
> On Sun, Mar 17, 2019 at 21:35 Emmanuel Vadot <manu_at_bidouilliste.com> wrote:
>
>> On Sun, 17 Mar 2019 16:32:43 +0000
>> Johannes Lundberg <johalun0_at_gmail.com> wrote:
>>
>>> On 3/17/19 3:34 PM, Greg V wrote:
>>>>
>>>> On Sun, Mar 17, 2019 at 3:07 PM, Johannes Lundberg
>>>> <johalun0_at_gmail.com> wrote:
>>>>> Hi
>>>>>
>>>>> I'm working on making i915kms unload properly. I've come to what I
>> think
>>>>> is the last issue. The drm driver unloads ok, the "efifb" backend is
>>>>> restored (according to logs) and vt_efifb_init() is being called but
>> the
>>>>> screen (laptop built in display) stays black. The system seems
>>>>> operational otherwise. If I load i915kms again in this state I get
>> back
>>>>> a visible (i915kms) framebuffer.
>>>>>
>>>>> Did we ever have this working so it's known to work?
>>>> Recently on the linux kernel mailing list:
>>>>
>>>> http://lkml.iu.edu/hypermail/linux/kernel/1903.1/01162.html
>>>>
>>>>> Of course, once native drivers like i915 or radeon take over, such a
>>>> framebuffer is toast... [6]
>>>>
>>>>> [6]
>> linux/drivers/gpu/drm/i915/i915_drv.c::i915_kick_out_firmware_fb()
>>>>> linux/drivers/gpu/drm/radeon/radeon_drv.c::radeon_pci_probe()
>>>> So it seems like efifb is not supposed to work after a driver has been
>>>> loaded at least once.
>>>>
>>>>
>>> Hmm, well the code is there to handle switching back to the boot time
>>> fb. What I think is happening is that i915 powers off the displays at
>>> unload and vt doesn't know how to power on (or that it should).
>>>
>>   That and if the display pipeline is de-configured or the resolution
>> changed you cannot reset it to the original state.
>>   Unloading drm modules is only useful for testing (and finding leaks).
>
> Yeah a normal user would never unload it. Since I mostly ssh to my test
> machines I think I’m fine personally with losing the display while
> unloading.
>
> Keyboard input still works though and at least it doesn’t crash anymore :)
>

that's awesome, so in theory we will be able to upgrade the drm-kmod and 
use the new driver without a reboot.  i like that as a hacker and 
end-user :)

-pete

-- 
Pete Wright
pete_at_nomadlogic.org
_at_nomadlogicLA