Hi

Am 26.09.22 um 12:34 schrieb Geert Uytterhoeven:
Hi Maxime,

On Mon, Sep 26, 2022 at 12:17 PM Maxime Ripard <max...@cerno.tech> 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 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.

Best regards
Thomas


Gr{oetje,eeting}s,

                         Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                 -- Linus Torvalds

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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