Nouveau - Sep 2022 - [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>

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 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 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
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 228 bytes
Desc: not available
URL:
<https://lists.freedesktop.org/archives/nouveau/attachments/20220926/00c5f847/attachment.sig>