On Mon, Sep 26, 2022 at 01:17:52PM +0200, Thomas Zimmermann wrote:
Hi
Am 26.09.22 um 12:34 schrieb Geert Uytterhoeven:
Hi Maxime,
On Mon, Sep 26, 2022 at 12:17 PM Maxime Ripard <maxime@xxxxxxxxxx> wrote:
On Fri, Sep 23, 2022 at 11:05:48AM +0200, Thomas Zimmermann wrote:
+ /* 63.556us * 13.5MHz = 858 pixels */
I kind of get what the comment wants to tell me, but the units don't add up.
I'm not sure how it doesn't add up?
We have a frequency in Hz (equivalent to s^-1) and a duration in s, so
the result ends up with no dimension, which is to be expected for a
number of periods?
To make the units add up, it should be 13.5 Mpixel/s
(which is what a pixel clock of 13.5 MHz really means ;-)
Sort of. It leaves the time value as a magic number, which obfuscates what's
happening.
The unit for htotal is pixels/scanline because if you multiply it with the
number of scanlines per frame (which is in vtotal), you get pixels/frame.
Multiplying with the frames per second results in the pixel clock in
pixels/second.
That's true, but both are true?
That's a bit much for this comment. Hence, I suggested to remove these
comments entirely and document the relation among the numbers in a more
prominent location. The documentation for drm_display_mode would be a good
place, I guess.
I'm not sure I understand what it's about. It's an explicit requirement
of PAL and NTSC, why would something so specific be in the generic
definition of drm_display_mode?
Maxime
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