linux-kernel - Re: [PATCH v2] drm/edid: Implement DisplayID Type IX & X timing blocks parsing

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Message-ID: <f0e0d4e7f5d552cb82cf3c9243f15772268fa311.camel@sdore.me>
Date: Thu, 13 Feb 2025 01:30:12 +0300
From: Egor Vorontsov <sdoregor@...re.me>
To: Jani Nikula <jani.nikula@...ux.intel.com>, linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org, Maarten Lankhorst
	 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
 Thomas Zimmermann <tzimmermann@...e.de>, Egor Vorontsov <sdoregor@...re.me>
Subject: Re: [PATCH v2] drm/edid: Implement DisplayID Type IX & X timing
 blocks parsing

On Wed, 2025-02-12 at 11:35 +0200, Jani Nikula wrote:
> > +	/* TODO: support video-optimized refresh rate */
> > +	if (timings->flags & (1 << 4))
> > +		return NULL;
> 
> Mmh. I'm not sure I'd go this far. The bit indicates *two* timings, one
> for which the below *is* correct, and another additional one with
> vrefresh * (1000/1001).
> 
> We could just add a drm_dbg_kms(dev, "<message>") here about missing
> fractional refresh rate, and proceed with the one non-fractional rate?
> Or just have the TODO comment with no checks.
I'll go with the former, for now.

> Either way,
> Reviewed-by: Jani Nikula <jani.nikula@...el.com>
Thank you. ... But!

> Are you up for the follow-ups too? And since you've got the hang of it,
> maybe fix struct displayid_formula_timings_9 hactive/vactive to __be16
> as well?
... at this moment I realised that both the specs and the legacy code
actually indicate it's indeed *little*-endian shorts!
I.e. `x[0] | x[1] << 8' -- that's LSB-first.

Also, virtually no code in `drm_edid.c' uses big-endian.

Thus, I'm fixing both my code and `displayid_detailed_timings_1' (I
suppose you meant this struct instead) to use __le16.

Egor