[External] Re: [PATCH] thinkpad_acpi: Add sysfs entry for lcdshadow feature

[Mark Pearson]

Hi Rajat,

> -----Original Message-----
> From: Rajat Jain <rajatja at google.com>
> Sent: Thursday, February 20, 2020 1:39 PM
> >
> > For this particular issue what is the best way to contribute and get
> > involved? We'd like to make it so ePrivacy can be used more easily from
> > Linux. I agree a more generic way of controlling it would be good.
> > I looked at the proposed patch from Rajat
> > (https://lkml.org/lkml/2019/10/22/967) - it seems like a good solution to me.
> > We can help with testing that on our platforms if that would be useful.
> 
> Thanks you, just so that you know, the latest patchset is at:
> https://lkml.org/lkml/2019/12/20/794
> 
> It would be great to get some additional testing if possible. I can
> send a sample ACPI (for our platform) in case it helps.
> 
Sounds good - we'll definitely try this out and see how it goes. I suspect we'll have some questions once we try it out and get more familiar.

> >
> > I need to understand how we connect that implementation with the ACPI
> > controls we have (as I believe what we have are thinkpad specific and not to
> > a drm spec; we need to confirm that). We also have the ACPI events that
> > notify if ePrivacy was changed by the hotkeys and that seems like something
> > that should be done in thinkpad_acpi.c and not the drm code.
> > 
> > Not sure if the two need to be connected somehow (or if handling the
> > event is actually not important and polling is acceptable)?
> 
> So there was some brief discussion about this on my patches - but
> atleast on  the platforms I have seen, there was no way to change the
> privacy screen out of software / kernel control. Essentially, if there
> are hotkeys, they would send an input event to the kernel, who'd send
> them to userspace, who'd use the DRM method to toggle the privacy
> screen. Thus the current version of the patch only supports
> controlling the privacy screen via set() method. The get() method just
> returns the cached value.I hope that works for you.
> 
OK - on the thinkpads we have function+D as a 'hotkey' to control the feature...and my understanding is that bypasses everything and goes straight to the firmware.

The changes Nitin had been working on in thinkpad_acpi.c was to make this more Linux and friendly - provide a sysfs hook for user space to connect to with the aim of allowing it to be configured from user space and have on screen display when it was triggered etc.

I'm personally not sure yet how this ties up with the DRM method - more digging required. I'm intrigued to see if it works on our systems (sadly I don't have anything with that feature available on my desk right now...I need to get my hands on one)

Thanks
Mark