[Intel-gfx] [PATCH 0/6] Intel Color Manager Framework

[Ville Syrjälä]

On Fri, Feb 21, 2014 at 02:20:24PM +0000, Sharma, Shashank wrote:
> Hi Ville, 
> 
> Thanks for your time and comments. 
> I can understand two basic problems what you see in this implementation: 
> 
> 1.  The most important issue from my POV is that it can't be part of the atomic modeset.    
> 2.  it make the whole API inconsistent. 
> 
> I am not sure if its good to block all current implementation because we have thought something for this in atomic modeset. 
> I think even in atomic modeset we need the core implementation like this, but the interface would be different, which might come in from of a DRM property. 
> So at that time we can use this core implementation as it is, only the interfaces/framework needs to be changed. 
> 
> In this way we can always go ahead with a current implementation, and can just change the interfaces to fit in to the final interface like DRM property in atomic modeset.
> Or you can suggest us the expected interface, and we can work on modifying that as per expectation.

The exptected interface will be range properties for stuff like
brightness, contrast etc. controls. There are already such things as
connector properties, but we're going to want something similar as
plane or crtc properties. One thing that worries me about such
properties though is whether we can make them hardware agnostic and
yet allow userspace precise control over the final image. That is, if we
map some fixed input range to a hardware specific output range, userspace
can't know how the actual output will change when the input changes. On
the other hand if the input is hardware specific, userspace can't know
what value to put in there to get the expected change on the output side.

For bigger stuff like CSC matrices and gamma ramps we will want to use
some reasonably well defined blobs. Ie. the internal strucuture of the
blob has to be documented and it shouldn't contain more than necessary.
Ie. just the CSC matrix coefficients for one matrix, or just the entries
for a single gamma ramp. Again ideally we should make the blobs hardware
agnostic, but still allow precise control over the output data.

I think this is going to involve first going over our hardware features,
trying to find the common patterns between different generations. If
there's a way to make something that works across the board for us, or
at least across a wide range, then we should also ask for some input on
dri-devel whether the proposed property would work for other people. We
may need to define new property types to more precisely define what the
value of the property actually means.

>  
> Please correct me if any of my assumptions are not right, or not feasible, or if I am just a moron :) .

The implementation itself has to be tied into the pipe config (and
eventual plane config) stuff, which are the structures meant to house
the full device state, which will then be applied in one go.

At the moment it looks like you're writing a bunch of registers from
various places w/o much thought into how those things interact with
anything else. For instance, what's the story with your use of the
pipe CSC unit vs. the already existing "Broadcast RGB" property?

>     
> Regards
> Shashank 
> -----Original Message-----
> From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com] 
> Sent: Friday, February 21, 2014 2:47 PM
> To: Sharma, Shashank
> Cc: intel-gfx at lists.freedesktop.org; Shankar, Uma; dri-devel at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH 0/6] Intel Color Manager Framework
> 
> On Fri, Feb 21, 2014 at 03:34:43AM +0000, Sharma, Shashank wrote:
> > Hi Ville/All,
> > 
> > We gave a presentation on design on this framework, few months ago, in one of our common forum with OTC folks. 
> > We  discussed, took review comments, and re-designed the framework, as per the feedbacks. 
> 
> Apparently I wasn't there. And in any case it would be better to discuss it on dri-devel where people outside Intel can give their opinion.
> 
> > 
> > We also discussed the benefits of providing the controls directly from /sysfs over going for a UI manager based property settings.
> > So I don't understand where are we going wrong, can you please elaborate a bit ? 
> 
> The most important issue from my POV is that it can't be part of the atomic modeset.
> 
> Another issue is that it make the whole API inconsistent. Some stuff through ioctl, some stuff through sysfs, some stuff through whatever the next guy thinks of. It's not pretty. I've worked in the past with a driver where I had to poke at various standardish ioctls, custom ioctls, and sysfs to make it do anything useful, and I have no interest in repeating that experience. sysfs is especially painful since you have do the string<->binary conversions all over the place, and also you en up doing open+read/write+close cycles for every little thing.
> 
> It also adds more entrypoints into the driver for us to worry about.
> That means extra worries about the power management stuff and locking at the very least.
> 
> Also the rules of sysfs say "one item per file". The only allowed exception to this rule I know of is hardware provided blobs (like EDID, PCI ROM etc.). Your current implementation breaks this rule blatantly.
> 
> > 
> > This is just a basic design, and once go ahead with this, we can always work on making hardware agnostic, as you recommended.  
> > 
> > IMHO, controls from /sysfs would be a very generic interface for all linux/drm based platform, where any userspace can read/write and control properties. 
> > We don't even need a UI manager or a minimum executable to play 
> > around, just a small script can do. But we can always write something on top of this, to be included in any UI framework or property.
> 
> If there's a real need to get at properties through sysfs, then we could think about exposing them all. But that may presents some issues where the current master suddenly gets confused about its state since someone else went behind its back and changed a bunch of stuff.
> 
> >  
> > Regards
> > Shashank    
> > 
> > -----Original Message-----
> > From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
> > Sent: Thursday, February 20, 2014 6:41 PM
> > To: Sharma, Shashank
> > Cc: intel-gfx at lists.freedesktop.org; Shankar, Uma; 
> > dri-devel at lists.freedesktop.org
> > Subject: Re: [Intel-gfx] [PATCH 0/6] Intel Color Manager Framework
> > 
> > On Thu, Feb 20, 2014 at 06:07:21PM +0530, Shashank Sharma wrote:
> > > Color manager is a new framework in i915 driver, which provides a 
> > > unified interface for various color correction methods supported by 
> > > intel hardwares. The high level overview of this change is:
> > 
> > Would have been good to discuss this idea before implementing it. The plan is to use kms properties for this kind of stuff which allows us to hook it up with the upcoming atomic modeset API. Just yesterday there was some discussion on #dri-devel about exposing user settable blob properties even before the atomic modeset API lands (it was always the plan for the atomic modeset API anyway). So based on a cursory glance, this looks like it's going in the wrong direction.
> > 
> > Also ideally the properties should be hardware agnostic, so a generic userspace could use them regardless of the hardware/driver. Obviously that might not be possible in all cases, but we should at least spend a bit of effort on trying to make that happen for most properties.
> > 
> > --
> > Ville Syrjälä
> > Intel OTC
> 
> --
> Ville Syrjälä
> Intel OTC

-- 
Ville Syrjälä
Intel OTC