linux-kernel - Re: [PATCH v6 16/23] drm/probe-helper: Provide a TV get

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Date:   Sun, 6 Nov 2022 17:59:23 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Mateusz Kwiatkowski <kfyatek@...il.com>, maxime@...no.tech,
        Karol Herbst <kherbst@...hat.com>,
        Emma Anholt <emma@...olt.net>, Ben Skeggs <bskeggs@...hat.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Samuel Holland <samuel@...lland.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Maxime Ripard <mripard@...nel.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Lyude Paul <lyude@...hat.com>
Cc:     linux-sunxi@...ts.linux.dev, intel-gfx@...ts.freedesktop.org,
        Phil Elwell <phil@...pberrypi.com>,
        linux-arm-kernel@...ts.infradead.org,
        nouveau@...ts.freedesktop.org, Hans de Goede <hdegoede@...hat.com>,
        Dom Cobley <dom@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Noralf Trønnes <noralf@...nnes.org>
Subject: Re: [PATCH v6 16/23] drm/probe-helper: Provide a TV get_modes helper



Den 27.10.2022 00.02, skrev Mateusz Kwiatkowski:
> Hi Maxime,
> 
> First of all, nice idea with the helper function that can be reused by different
> drivers. This is neat!
> 
> But looking at this function, it feels a bit overcomplicated. You're creating
> the two modes, then checking which one is the default, then set the preferred
> one and possibly reorder them. Maybe it can be simplified somehow?
> 
> Although when I tried to refactor it myself, I ended up with something that's
> not better at all. Maybe it needs to be complicated, after all :(
> 

I also thought that the function was complicated/difficult to read, in
particular the index stuff at the end, but I also failed in finding a
"better" solution, just a different one ;)

Noralf.

My version:

int drm_connector_helper_tv_get_modes(struct drm_connector *connector)
{
	struct drm_device *dev = connector->dev;
	struct drm_property *tv_mode_property = dev->mode_config.tv_mode_property;
	struct drm_cmdline_mode *cmdline = &connector->cmdline_mode;
	unsigned int ntsc_modes = BIT(DRM_MODE_TV_MODE_NTSC) |
				  BIT(DRM_MODE_TV_MODE_NTSC_443) |
				  BIT(DRM_MODE_TV_MODE_NTSC_J) |
				  BIT(DRM_MODE_TV_MODE_PAL_M);
	unsigned int pal_modes = BIT(DRM_MODE_TV_MODE_PAL) |
				 BIT(DRM_MODE_TV_MODE_PAL_N) |
				 BIT(DRM_MODE_TV_MODE_SECAM);
	unsigned int tv_modes[2] = { UINT_MAX, UINT_MAX };
	unsigned int i, supported_tv_modes = 0;

	if (!tv_mode_property)
		return 0;

	for (i = 0; i < tv_mode_property->num_values; i++)
		supported_tv_modes |= BIT(tv_mode_property->values[i]);

	if ((supported_tv_modes & ntsc_modes) && (supported_tv_modes &
pal_modes)) {
		uint64_t default_mode;

		if (drm_object_property_get_default_value(&connector->base,
							  tv_mode_property,
							  &default_mode))
			return 0;

		if (cmdline->tv_mode_specified)
			default_mode = cmdline->tv_mode;

		if (BIT(default_mode) & ntsc_modes) {
			tv_modes[0] = DRM_MODE_TV_MODE_NTSC;
			tv_modes[1] = DRM_MODE_TV_MODE_PAL;
		} else {
			tv_modes[0] = DRM_MODE_TV_MODE_PAL;
			tv_modes[1] = DRM_MODE_TV_MODE_NTSC;
		}
	} else if (supported_tv_modes & ntsc_modes) {
		tv_modes[0] = DRM_MODE_TV_MODE_NTSC;
	} else if (supported_tv_modes & pal_modes) {
		tv_modes[0] = DRM_MODE_TV_MODE_PAL;
	} else {
		return 0;
	}
	
	for (i = 0; i < ARRAY_SIZE(tv_modes); i++) {
		struct drm_display_mode *mode;

		if (tv_modes[i] == DRM_MODE_TV_MODE_NTSC)
			mode = drm_mode_analog_ntsc_480i(dev);
		else if (tv_modes[i] == DRM_MODE_TV_MODE_PAL)
			mode = drm_mode_analog_pal_576i(dev);
		else
			break;
		if (!mode)
			return i;
		if (!i)
			mode->type |= DRM_MODE_TYPE_PREFERRED;
		drm_mode_probed_add(connector, mode);
	}

	return i;
}