Re: [Intel-gfx] [PATCH v2 02/20] drm: Don't update plane properties for atomic planes if it stays the same

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 13-07-15 om 11:13 schreef Daniel Vetter:
> On Mon, Jul 13, 2015 at 10:59:32AM +0200, Maarten Lankhorst wrote:
>> Op 08-07-15 om 22:12 schreef Daniel Vetter:
>>> On Wed, Jul 08, 2015 at 08:25:07PM +0200, Maarten Lankhorst wrote:
>>>> Op 08-07-15 om 19:52 schreef Daniel Vetter:
>>>>> On Wed, Jul 08, 2015 at 06:35:47PM +0200, Maarten Lankhorst wrote:
>>>>>> Op 08-07-15 om 10:55 schreef Daniel Vetter:
>>>>>>> On Wed, Jul 08, 2015 at 10:00:22AM +0200, Maarten Lankhorst wrote:
>>>>>>>> Op 07-07-15 om 18:43 schreef Daniel Vetter:
>>>>>>>>> On Tue, Jul 07, 2015 at 05:08:34PM +0200, Maarten Lankhorst wrote:
>>>>>>>>>> Op 07-07-15 om 14:10 schreef Daniel Vetter:
>>>>>>>>>>> On Tue, Jul 07, 2015 at 12:20:10PM +0200, Maarten Lankhorst wrote:
>>>>>>>>>>>> Op 07-07-15 om 11:18 schreef Daniel Vetter:
>>>>>>>>>>>>> On Tue, Jul 07, 2015 at 09:08:13AM +0200, Maarten Lankhorst wrote:
>>>>>>>>>>>>>> This allows the first atomic call during hw init to be a real modeset,
>>>>>>>>>>>>>> which is useful for forcing a recalculation.
>>>>>>>>>>>>> fbcon is optional, you can't rely on anything being done in any specific
>>>>>>>>>>>>> way. What exactly do you need this for, what's the implications?
>>>>>>>>>>>> In the hw readout I noticed some warnings when I wasn't setting any mode property in the readout.
>>>>>>>>>>>> I want the first function to be the modeset, so we have a sane base to commit changes on.
>>>>>>>>>>>> Ideally this whole function would have a atomic counterpart which does it in one go. :)
>>>>>>>>>>> Yeah. Otoh as soon as we have atomic modeset working we can replace all
>>>>>>>>>>> the legacy entry points with atomic helpers, and then even plane_disable
>>>>>>>>>>> will be a full atomic modeset.
>>>>>>>>>>>
>>>>>>>>>>> What did fall apart with just touching properties/planes now?
>>>>>>>>>> Also when i915 is fully atomic it calculates in intel_modeset_compute_config
>>>>>>>>>> if a modeset is needed after the first atomic call. Right now because
>>>>>>>>>> intel_modeset_compute_config is only called in set_config so this works as expected.
>>>>>>>>>> Otherwise drm_plane_force_disable or rotate_0 will force a modeset,
>>>>>>>>>> and if the final mode is different this will introduce a double modeset.
>>>>>>>>> For expensive properties (i.e. a no-op changes causes something that takes
>>>>>>>>> time like modeset or vblank wait) we need to make sure we filter them out
>>>>>>>>> in atomic_check. Yeah not quite there yet with pure atomic, but meanwhile
>>>>>>>>> the existing legacy set_prop functions should all filter out no-op changes
>>>>>>>>> themselves. If we don't do that for rotation then that's a bug.
>>>>>>>>>
>>>>>>>>> Same for disabling planes harder, that shouldn't take time. Especially
>>>>>>>>> since fbcon only force-disable non-primary plane, and for driver load
>>>>>>>>> that's the exact thing we already do in the driver anyway.
>>>>>>>> Something like this?
>>>>>>>> ---
>>>>>>>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>>>>>>>> index a1d4e13f3908..2989232f4996 100644
>>>>>>>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>>>>>>>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>>>>>>>> @@ -30,6 +30,7 @@
>>>>>>>>  #include <drm/drm_plane_helper.h>
>>>>>>>>  #include <drm/drm_crtc_helper.h>
>>>>>>>>  #include <drm/drm_atomic_helper.h>
>>>>>>>> +#include "drm_crtc_internal.h"
>>>>>>>>  #include <linux/fence.h>
>>>>>>>>  
>>>>>>>>  /**
>>>>>>>> @@ -1716,7 +1717,12 @@ drm_atomic_helper_crtc_set_property(struct drm_crtc *crtc,
>>>>>>>>  {
>>>>>>>>  	struct drm_atomic_state *state;
>>>>>>>>  	struct drm_crtc_state *crtc_state;
>>>>>>>> -	int ret = 0;
>>>>>>>> +	uint64_t retval;
>>>>>>>> +	int ret;
>>>>>>>> +
>>>>>>>> +	ret = drm_atomic_get_property(&crtc->base, property, &retval);
>>>>>>>> +	if (!ret && val == retval)
>>>>>>>> +		return 0;
>>>>>>>>  
>>>>>>>>  	state = drm_atomic_state_alloc(crtc->dev);
>>>>>>>>  	if (!state)
>>>>>>>> @@ -1776,7 +1782,12 @@ drm_atomic_helper_plane_set_property(struct drm_plane *plane,
>>>>>>>>  {
>>>>>>>>  	struct drm_atomic_state *state;
>>>>>>>>  	struct drm_plane_state *plane_state;
>>>>>>>> -	int ret = 0;
>>>>>>>> +	uint64_t retval;
>>>>>>>> +	int ret;
>>>>>>>> +
>>>>>>>> +	ret = drm_atomic_get_property(&plane->base, property, &retval);
>>>>>>>> +	if (!ret && val == retval)
>>>>>>>> +		return 0;
>>>>>>>>  
>>>>>>>>  	state = drm_atomic_state_alloc(plane->dev);
>>>>>>>>  	if (!state)
>>>>>>>> @@ -1836,7 +1847,12 @@ drm_atomic_helper_connector_set_property(struct drm_connector *connector,
>>>>>>>>  {
>>>>>>>>  	struct drm_atomic_state *state;
>>>>>>>>  	struct drm_connector_state *connector_state;
>>>>>>>> -	int ret = 0;
>>>>>>>> +	uint64_t retval;
>>>>>>>> +	int ret;
>>>>>>>> +
>>>>>>>> +	ret = drm_atomic_get_property(&connector->base, property, &retval);
>>>>>>>> +	if (!ret && val == retval)
>>>>>>>> +		return 0;
>>>>>>>>  
>>>>>>>>  	state = drm_atomic_state_alloc(connector->dev);
>>>>>>>>  	if (!state)
>>>>>>> The reason I didn't do this is that a prop change might still result in no
>>>>>>> hw state change (e.g. if you go automitic->explicit setting matching
>>>>>>> automatic one). Hence I think we need to solve this in lower levels
>>>>>>> anyway, i.e. in when computing the config. But it shouldn't cause trouble
>>>>>>> yet.
>>>>>> Is that a ack or nack?
>>>>> I think we shouldn't need this really for i915, and it might cover up
>>>>> bugs. I prefer we just do the evade modeset logic you've implemented once
>>>>> we switch over to atomic props. Since atm we only have atomic props which
>>>>> get updated in pageflips we shouldn't have serious problems here yet (for
>>>>> setting the rotation prop to 0° again when fbdev starts up).
>>>>>
>>>>> Or do I miss something still here?
>>>> Yes, if the hardware mode is incompatible with its calculated sw mode,
>>>> and we set a different mode from fbdev you get 2 modesets instead of 1.
>>> How does that happen? For setting the rotation property we should just
>>> duplicate the current crtc state. Since there's no mode changing (they
>>> should match perfectly no matter how botched the reconstruction is) there
>>> shouldn't be any need to recompute the config completely and discover that
>>> there's a mismatch. Which means we'll just do the plane update (which
>>> might do a few silly mmios but shouldn't block) and that's it.
>>>
>>> At least that's what I'd expect - where does this fall apart?
>> If crtc is active and primary fb visible, and converted to atomic:
>>
>> restore_fbdev_mode() ->
>> 	drm_mode_plane_set_obj_prop() ->
>> 		drm_atomic_helper_plane_set_property() ->
>> 			drm_atomic_get_plane_state() ->
>> 				drm_atomic_get_crtc_state()
>> crtc state is part of the state, intel_modeset_pipe_config performs
>> the initial check if modeset's needed. Lets assume yes:
> "Let's assume yes" -> that's imo a bug, so where does this happen so that
> we can fix it? Disabling a plane or setting a plane prop really shouldn't
> result in a modeset. Well at least if it's not a plane prop that does
> required a modeset (but I don't think we have any of those).
From a driver point of view you wouldn't be able to distinguish it from a real modeset to the same mode. :(
In both cases you have all planes added and the crtc.

Thinking about it more there will be 1 thing saving us from a modeset,
drm_atomic_crtc_check will reject enable without mode_blob for atomic drivers,
so until the first mode is set all atomic updates to the crtc will be rejected.

Unfortunately you will still get WARN_ON's for this, so a better solution's needed.

~Maarten

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