Hello, Maarten!
On 02/01/2018 12:13 PM, Oleksandr Andrushchenko wrote:
On 02/01/2018 12:04 PM, Maarten Lankhorst wrote:
Op 01-02-18 om 08:08 schreef Oleksandr Andrushchenko:
Hi, all!
I am working on a para-virtualized frontend DRM driver for Xen [1]
which implements display device I/O interface for Xen guest OSes [2].
At the moment I am rebasing the existing implementation from 4.9 kernel
to recent and found that when user-space DRM application exits then
CRTC's
.set_config callback is not called to reset CRTC's mode to NULL.
I tracked the change down to commit
846c7dfc1193eb2f9866fe2fa0ae7d45c72f95b9
"drm/atomic: Try to preserve the crtc enabled state in
drm_atomic_remove_fb, v2.
This introduces a slight behavioral change to rmfb. Instead of
disabling a crtc when the primary plane is disabled, we try to
preserve it.
<snip>
If the atomic commit is rejected by the driver then we will still
fall back to the old behavior and turn off the crtc.
"
which per my understanding is ok for real hardware, but in my case I
still
need .set_config to be called with NULL: this way I can tell the
backend
driver that it can release resources for this connection on its end.
I tried to implement drm_mode_config_funcs's .atomic_commit
returning -EINVAL
on tear down, but at best it made CRTC's atomic state change to
NOCRTC, but
still no .set_config callback seen.
Can anyone please tell me the right sequence to implement old remove FB
behavior for atomic drivers? Or what could be the problem on my side?
rmfb was never meant to mean that the crtc will be disabled as well.
vmwgfx relied on that
behavior as well for old userspace support because userspace never
called set_config.
If you're an atomic driver, the driver core will never call
set_config any more, even if the
first attempt to disable returns -EINVAL. Even the fbcon helpers now
perform direct
calls to atomic_commit().
understood, thank you for clarification
I started to re-implement the existing code in my driver to comply to the
new atomic behavior in terms of "the driver core will never call
set_config any more"
and the question now is what would be the right place to put a check for
mode change?
Basically, I would like to know where I can get "struct drm_mode_set" as
I used to have in drm_crtc_funcs.set_config callback? Or some other
source of
information I can derive (x,y), (width,height), pixel format for the mode
when it changes.
Candidates I am playing with are:
1. drm_crtc_helper_funcs.atomic_flush
2. drm_mode_config_funcs.atomic_commit
During experiments with the above I see that during "on" phase in the
drm_crtc_state I can see that mode, enable and active fields of the state
are changed to 1, but during the "off" phase they remain at 1.
Then I added the primary plane check from drm_simple_kms_crtc_check
and at "off" those started to change to 0.
Do you think drm_mode_config_funcs.atomic_commit with the above
changes/checks
will be the right way to get knowledge to emulate old ".set_config"?
I am trying to be a new atomic driver, but due to the protocol [2]
requirements
I still need a way to send .set_config request to the backend.
If you then still want to revert to old behavior and it doesn't make
sense to have the
crtc enabled without primary plane enabled, you can copy the check
from drm_simple_kms_crtc_check().
will try that, but at the moment this is not a strict requirement
anymore,
just wanted to make sure I understand the flow correctly
~Maarten
Thank you,
Oleksandr
Thank you,
Oleksandr
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