From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp-68.nebula.fi ([83.145.220.68]:54426 "EHLO smtp-68.nebula.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751805Ab2AJK5z (ORCPT ); Tue, 10 Jan 2012 05:57:55 -0500 Message-ID: <4F0C19AE.3090501@iki.fi> Date: Tue, 10 Jan 2012 12:57:50 +0200 From: Sakari Ailus MIME-Version: 1.0 To: Laurent Pinchart CC: linux-media@vger.kernel.org, tuukkat76@gmail.com, dacohen@gmail.com, g.liakhovetski@gmx.de, hverkuil@xs4all.nl, snjw23@gmail.com Subject: Re: [ANN] Notes on IRC meeting on new sensor control interface, 2012-01-09 14:00 GMT+2 References: <20120104085633.GM3677@valkosipuli.localdomain> <201201101050.52887.laurent.pinchart@ideasonboard.com> <4F0C0A5A.9060708@iki.fi> <201201101105.49477.laurent.pinchart@ideasonboard.com> In-Reply-To: <201201101105.49477.laurent.pinchart@ideasonboard.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi Laurent, Laurent Pinchart wrote: > On Tuesday 10 January 2012 10:52:26 Sakari Ailus wrote: >> Laurent Pinchart wrote: >>> On Tuesday 10 January 2012 10:42:58 Sakari Ailus wrote: >>>> Laurent Pinchart wrote: >>>>> On Tuesday 10 January 2012 00:26:46 Sakari Ailus wrote: >>>>>> Laurent Pinchart wrote: >>>>>>> On Monday 09 January 2012 23:32:06 Sakari Ailus wrote: >>>>>>>> Laurent Pinchart wrote: >>>>>>>>> On Monday 09 January 2012 18:38:25 Sakari Ailus wrote: >>>>>> ... >>>>>> >>>>>>>>>> A fourth section may be required as well: at this level the frame >>>>>>>>>> rate (or frame time) range makes more sense than the low-level >>>>>>>>>> blanking values. The blanking values can be calculated from the >>>>>>>>>> frame time and a flag which tells whether either horizontal or >>>>>>>>>> vertical blanking should be preferred. >>>>>>>>> >>>>>>>>> How does one typically select between horizontal and vertical >>>>>>>>> blanking ? Do mixed modes make sense ? >>>>>>>> >>>>>>>> There are minimums and maximums for both. You can increase the frame >>>>>>>> time by increasing value for either or both of them --- to achieve >>>>>>>> very long frame times you may have to use both, but that's not very >>>>>>>> common in practice. I think we should have a flag to tell which one >>>>>>>> should be increased first --- the effect would be to have the >>>>>>>> minimum possible value on the other. >>>>>>> >>>>>>> But how do you decide in practice which one to increase when you're >>>>>>> an application (or middleware) developer ? >>>>>> >>>>>> I think it's the responsibility of this library to do that, unless the >>>>>> user wants really, really precise control in which case they have to >>>>>> deal with the blanking values directly. In general it should be the >>>>>> library. >>>>> >>>>> And how does the library decide ? :-) >>>> >>>> frame_time = pixel_rate / ((width + hblank) * (height + vblank)) >>>> >>>> The user gives you frame time and the configuration contains the >>>> information which one to prefer. Let's say the user prefers hblank (from >>> >>>> the above): >>> That was my question, how does the user decide whether hblank or vblank >>> is preferred ? >> >> I think that should be defined in the configuration itself. It's very >> unlikely there's any need to change this dynamically. > > Sure, but that's not my point. How does the user decide in the first place > when writing the configuration ? That's a policy decision. There may be multiple reasons for that, but the most obvious I can think of is a decision between amortised memory access rate and the rolling shutter effect. There may be other factors like time of year, phase of moon and colour of the neighbour's cat to name a few. :-) It might also make sense to be able to specify a minimum for horizontal blanking which is bigger than the minimum the sensor allows. But that's going to the fine details. -- Sakari Ailus sakari.ailus@iki.fi