Hi,
On 9/17/21 6:25 PM, Ville Syrjälä wrote:
On Fri, Sep 17, 2021 at 04:37:14PM +0200, Hans de Goede wrote:
Hi,
On 9/16/21 3:45 PM, Ville Syrjälä wrote:
On Mon, Sep 06, 2021 at 09:35:19AM +0200, Hans de Goede wrote:
Add support for eDP panels with a built-in privacy screen using the new drm_privacy_screen class.
One thing which stands out here is the addition of these 2 lines to intel_atomic_commit_tail:
for_each_new_connector_in_state(&state->base, connector, ... drm_connector_update_privacy_screen(connector, state);
It may seem more logical to instead take care of updating the privacy-screen state by marking the crtc as needing a modeset and then do this in both the encoder update_pipe (for fast-sets) and enable (for full modesets) callbacks. But ATM these callbacks only get passed the new connector_state and these callbacks are all called after drm_atomic_helper_swap_state() at which point there is no way to get the old state from the new state.
Pretty sure the full atomic state is plumbed all the way down these days.
Including the old state? AFAICT the old-state is being thrown away from drm_atomic_helper_swap_state(),
No. That's just when those annoying foo_state->state pointers get clobbered. We've been moving away from using those and just plumbing the entire atomic state everywhere.
Nothing actually gets freed until the whole drm_atomic_state gets nuked after the commit is done.
so if we do this in a different place then we don't have access to the old-state.
Without access to the old state, we do not know if the sw_state of the privacy-screen has changes so we would need to call drm_privacy_screen_set_sw_state() unconditionally. This is undesirable since all current known privacy-screen providers use ACPI calls which are somewhat expensive to make.
I doubt anyone is going to care about a bit of overhead for a modeset.
But this is not a modeset, this is more like changing the backlight brightness, atm the code does not set the needs_modeset when only the privacy-screen sw-state has changed.
Also in my experience the firmware (AML) code which we end up calling for this is not the highest quality code, often it has interesting issues / unhandled corner cases. So in my experience with ACPI we really should try to avoid these calls unless we absolutely must make them, but I guess not making unnecessary calls is something which could be handled inside the actual privacy-screen driver instead.
The usual rule is that a modeset doesn't skip anything. That way we can be 100% sure we remeber to update everythinbg. For fastsets I guess one could argue skipping it if not needed, but not sure even that is warranted.
Right, but again this is not a full modeset.
In general fastset is is just an optimized modeset. Userspace asked for a modeset, but we noticed it doesn't need it. I don't think there is a particular expectation that it's super fast.
But if this is really annoyingly slow in some actual usecase
Yeah these acpi-calls might take like a 100 ms easily, so we really want to avoid it if it is not necessary.
then one way to avoid that need to compare against the old state is just introduce another foo_changed flag.
Ok, so I have the feeling that you have an idea of how you think this should be done / how this code should look instead of what I have currently.
Can you perhaps provide a rough sketch / description of how you think this should be done (instead of the current implementation) ?
Should I do the update from the the encoder update_pipe (for fast-sets) and enable (for full modesets) callbacks instead as I mention in the commit message ?
And since I still only want to do the call if there is an actual change, where could I best do the old / new sw_state change cmp to set the new foo_changed flag?
The current code you have in there is cettainly 110% dodgy. Since the sw_state is stored in the connector state I presume it's at least trying to be an atomic property, which means you shouldn't go poking at it after the swap_state ever.
It is not being poked, it is only being read, also this is happening before swap_state.
Note I'm open for suggestions to handle this differently, including changing the drm_connector_update_privacy_screen() helper which currently relies on being passed the state before swap_state is called:
void drm_connector_update_privacy_screen(struct drm_connector *connector, struct drm_atomic_state *state) { struct drm_connector_state *new_connector_state, *old_connector_state; int ret;
if (!connector->privacy_screen) return;
new_connector_state = drm_atomic_get_new_connector_state(state, connector); old_connector_state = drm_atomic_get_old_connector_state(state, connector);
if (new_connector_state->privacy_screen_sw_state == old_connector_state->privacy_screen_sw_state) return;
ret = drm_privacy_screen_set_sw_state(connector->privacy_screen, new_connector_state->privacy_screen_sw_state); if (ret) { drm_err(connector->dev, "Error updating privacy-screen sw_state\n"); return; }
So if you have any suggestions how to do this differently, please let me know and I will take a shot at implementing those suggestions.
You cut the code too soon. Just after this you call the other update_privacy_screen() thing which does poke at connector->state->stuff AFAICS.
True, the idea here is to only update the hw_state, the returned sw_state should always be the one which we just set. But I agree it would be better to change the code here so that drm_connector_update_privacy_screen() only updates privacy_screen_hw_state I will change the code to do this in the next version of this patch-set.
Regards,
Hans