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From: Keith Packard <keithp@keithp.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
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Cc: Tomasz Stanislawski <t.stanislaws@samsung.com>,
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Subject: Re: Kernel Display and Video API Consolidation mini-summit at ELC 2012 - Notes
In-Reply-To: <1775349.d0yvHiVdjB@avalon>
References: <201201171126.42675.laurent.pinchart@ideasonboard.com> <1654816.MX2JJ87BEo@avalon> <1775349.d0yvHiVdjB@avalon>
Date: Sat, 18 Feb 2012 13:56:49 +1300
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<#part sign=pgpmime>
On Fri, 17 Feb 2012 00:25:51 +0100, Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote:

> ***  Synchronous pipeline changes ***
> 
>   Goal: Create an API to apply complex changes to a video pipeline atomically.
> 
>   Needed for complex camera use cases. On the DRM/KMS side, the approach is to
>   use one big ioctl to configure the whole pipeline.

This is the only credible approach for most desktop chips -- you must
have the whole configuration available before you can make any
commitment to supporting the requested modes.

>   One solution is a commit ioctl, through the media controller device, that
>   would be dispatched to entities internally with a prepare step and a commit
>   step.

The current plan for the i915 KMS code is to use a single ioctl -- the
application sends a buffer full of configuration commands down to the
kernel which can then figure out whether it can be supported or not.

The kernel will have to store the intermediate data until the commit
arrives anyways, and you still need a central authority in the kernel
controlling the final commit decision.

-- 
keith.packard@intel.com