Hi Am 11.07.22 um 11:35 schrieb Geert Uytterhoeven:
Hi Thomas, On Mon, Jul 11, 2022 at 11:03 AM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:Am 08.07.22 um 20:21 schrieb Geert Uytterhoeven:The mode parsing code recognizes named modes only if they are explicitly listed in the internal whitelist, which is currently limited to "NTSC" and "PAL". Provide a mechanism for drivers to override this list to support custom mode names. Ideally, this list should just come from the driver's actual list of modes, but connector->probed_modes is not yet populated at the time of parsing.I've looked for code that uses these names, couldn't find any. How is this being used in practice? For example, if I say "PAL" on the command line, is there DRM code that fills in the PAL mode parameters?I guess Maxime knows, as he added the whitelist?
Yeah, I saw his reply already.
I don't really have a strong opinion, but having all modes in one global list is quite user-friendly. It's all there for everyone. Otherwise users would somehow have to know which hardware supports which modes. That's actually the job of each driver's mode_valid and atomic_check functions.Reading the description of commit 3764137906a5acec ("drm/modes: Introduce a whitelist for the named modes"), it looks like this is more about preventing the parser from taking any string as a random mode, than about adding support for "PAL" or "NTSC"? Note that drivers/gpu/drm/i915/display/intel_tv.c defines an array of tv_modes[], including "PAL", so perhaps these end up as named modes?And another question I have is whether this whitelist belongs into the driver at all. Standard modes exist independent from drivers or hardware. Shouldn't there simply be a global list of all possible mode names? Drivers would filter out the unsupported modes anyway.For standard modes, I agree. And these are usually specified by resolution and refresh rate (e.g. "640x480@60", instead of "480p"). But legacy hardware may have very limited support for programmable pixel clocks (e.g. Amiga is limited to pixel clocks of 7, 14, or 28 MHz), so the standard modes are a bad match, or may not work at all. Hence drivers may need to provide their own modes, but it seems wrong to me to make these non-standard modes global, and possibly pollute the experience for everyone.
Best regards Thomas
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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