Re: [PATCH 09/21] OMAPDSS: DISPC: Calculate scaling limits in a more generic way

On Friday 14 September 2012 02:23 PM, Tomi Valkeinen wrote:

On Thu, 2012-09-13 at 17:44 +0530, Archit Taneja wrote:

quoted

Scaling calculations for an overlay are done by comparing pixel clock of the
connected overlay manager and the core clock of DISPC. The pixel clock is the
output rate of the scalar. The scalar block needs to provide pixels at this rate
since the manager is connected to a panel, which has real time constraints.

In the case of writeback in memory to memory mode, the output of the scalar
blocks aren't connected to a display, and hence there isn't a pixel clock which
causes downscaling limitations.

Make the input to scaling calculations a bit more generic by passing the scalar
output rate rather than passing pixel clock of the overlay manager connected to
the pipeline, as we now have use cases where the scalar's output may not go to
a manager connected to a panel.

Pixel clock is the rate at which pixels are processed. I don't see it
only meaning a clock that's related to actual video signal going out of
OMAP. So if in normal case the scaler outputs pixels at the rate of
pixel clock, we can call it pixel clock with WB's case also, instead of
renaming it to output clock.

Pixel clock, in OMAP DSS terms, is the rate at which the video port of 
an overlay manager provides pixels to an output. It is a fixed rate at 
which the scaler needs to push out data.

If we stick to this terminology of pixel clock, I don't think it applies 
to writeback. As far as I see it, there is no specific rate at which the 
scaler outputs data, it adjusts itself based on how much scaling is 
done, and at the rate we can get/push data to the interconnect. That's 
why I didn't want to call it pixel clock. Because, that sounds a lot 
like a fixed rate at which pixels need to be output.

Or was there some other reason for the rename, that I missed?

The main aim of this patch was to pass pixel clock rate/or output rate 
as an argument to scaler functions, rather than passing the overlay 
manager's channel id to calculate this rate. I can rename it to pixel 
clock if that seems better.

Archit