Geert Uytterhoeven
2022-Sep-26 10:34 UTC
[Nouveau] [PATCH v2 10/33] drm/modes: Add a function to generate analog display modes
Hi Maxime, On Mon, Sep 26, 2022 at 12:17 PM Maxime Ripard <maxime at 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 ;-) Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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
2022-Sep-26 11:17 UTC
[Nouveau] [PATCH v2 10/33] drm/modes: Add a function to generate analog display modes
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 at 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 -- geert at 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 N?rnberg, Germany (HRB 36809, AG N?rnberg) Gesch?ftsf?hrer: Ivo Totev -------------- next part -------------- A non-text attachment was scrubbed... Name: OpenPGP_signature Type: application/pgp-signature Size: 840 bytes Desc: OpenPGP digital signature URL: <https://lists.freedesktop.org/archives/nouveau/attachments/20220926/11335383/attachment.sig>