Hi,
On 4/15/20 11:10 PM, Jani Nikula wrote:
On Wed, 15 Apr 2020, Rajat Jain rajatja@google.com wrote:
Hello,
On Wed, Apr 15, 2020 at 8:40 AM Hans de Goede hdegoede@redhat.com wrote:
Hi,
On 4/15/20 5:28 PM, Jani Nikula wrote:
On Wed, 15 Apr 2020, Hans de Goede hdegoede@redhat.com wrote:
ii. Currently the "privacy-screen" property added by Rajat's patch-set is an enum with 2 possible values: "Enabled" "Disabled"
We could add a third value "Not Available", which would be the default and then for internal panels always add the property so that we avoid the problem that detecting if the laptop has an internal privacy screen needs to be done before the connector is registered. Then we can add some hooks which allow an lcdshadow-driver to register itself against a connector later (which is non trivial wrt probe order, but lets ignore that for now).
I regret dropping the ball on Rajat's series (sorry!).
I do think having the connector property for this is the way to go.
I 100% agree.
Even if we couldn't necessarily figure out all the details on the kernel internal connections, can we settle on the property though, so we could move forward with Rajat's series?
Thanks, it would be great!.
Yes please, this will also allow us to move forward with userspace support even if for testing that we do some hacks for the kernel's internal connections for now.
Moreover, do we actually need two properties, one which could indicate userspace's desire for the property, and another that tells the hardware state?
No I do not think so. I would expect there to just be one property, I guess that if the state is (partly) firmware controlled then there might be a race, but we will need a notification mechanism (*) for firmware triggered state changes anyways, so shortly after loosing the race userspace will process the notification and it will know about it.
I agree with Hans here that I think it would be better if we could do it with one property.
- I can imagine demand for laptops that have a "hardware kill switch"
for privacy screen (just like there are for camera etc today). So I think in future we may have to deal with this case anyway. In such devices it's the hardware (as opposite to firmware) that will change the state. The HW will likely provide an interrupt to the software to notify of the change. This is all imaginative at this point though.
- I think having 2 properties might be a confusing UAPI. Also, we have
existing properties like link-status that can be changed by both the user and the hardware.
I think the consensus is that all properties that get changed by both userspace and the kernel are mistakes, and the way to handle it is to have two properties.
But the actual privacy screen has only 1 state, having two properties for this will only be confusing. As I mentioned before we have a similar case with e.g. keyboard backlighting and there the userspace API also has a single sysfs attribute for the brightness, with change notifications to userspace if the firmware changes the brightness on its own and this works well.
What would the semantics of these 2 different properties be? And what sort of extra functionality would these semantics offer which the single property versions does not offer?
Regards,
Hans