linux-kernel - Re: [PATCH 4/5] drm/modes: Add support for driver-specific named modes

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Message-ID: <ef2aada2-96e4-c2e4-645f-39bc9094e93a@suse.de>
Date:   Mon, 11 Jul 2022 11:03:38 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Hans de Goede <hdegoede@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-m68k@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] drm/modes: Add support for driver-specific named
 modes

Hi Geert

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?

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.

Best regards
Thomas

> 
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
>   drivers/gpu/drm/drm_modes.c | 15 +++++++++++----
>   include/drm/drm_connector.h | 10 ++++++++++
>   2 files changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 9ce275fbda566b7c..7a00eb6df502e991 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1748,25 +1748,31 @@ static int drm_mode_parse_cmdline_options(const char *str,
>   static const char * const drm_named_modes_whitelist[] = {
>   	"NTSC",
>   	"PAL",
> +	NULL
>   };
>   
>   static int drm_mode_parse_cmdline_named_mode(const char *name,
>   					     unsigned int length,
>   					     bool refresh,
> +					     const struct drm_connector *connector,
>   					     struct drm_cmdline_mode *mode)
>   {
> +	const char * const *named_modes_whitelist;
>   	unsigned int i;
>   	int ret;
>   
> -	for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
> -		ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
> +	named_modes_whitelist = connector->named_modes_whitelist ? :
> +				drm_named_modes_whitelist;
> +
> +	for (i = 0; named_modes_whitelist[i]; i++) {
> +		ret = str_has_prefix(name, named_modes_whitelist[i]);
>   		if (!ret)
>   			continue;
>   
>   		if (refresh)
>   			return -EINVAL; /* named + refresh is invalid */
>   
> -		strcpy(mode->name, drm_named_modes_whitelist[i]);
> +		strcpy(mode->name, named_modes_whitelist[i]);
>   		mode->specified = true;
>   		return 0;
>   	}
> @@ -1850,7 +1856,8 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
>   	/* First check for a named mode */
>   	if (mode_end) {
>   		ret = drm_mode_parse_cmdline_named_mode(name, mode_end,
> -							refresh_ptr, mode);
> +							refresh_ptr, connector,
> +							mode);
>   		if (ret)
>   			return false;
>   	}
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 3ac4bf87f2571c4c..6361f8a596c01107 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -1659,6 +1659,16 @@ struct drm_connector {
>   
>   	/** @hdr_sink_metadata: HDR Metadata Information read from sink */
>   	struct hdr_sink_metadata hdr_sink_metadata;
> +
> +	/**
> +	 * @named_modes_whitelist:
> +	 *
> +	 * Optional NULL-terminated array of names to be considered valid mode
> +	 * names.  This lets the command line option parser distinguish between
> +	 * mode names and freestanding extras and/or options.
> +	 * If not set, a set of defaults will be used.
> +	 */
> +	const char * const *named_modes_whitelist;
>   };
>   
>   #define obj_to_connector(x) container_of(x, struct drm_connector, base)

-- 
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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