linux-kernel - Re: [PATCH v4 3/3] drm/panel-simple: allow LVDS format override

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Date:   Fri, 18 Aug 2023 09:04:34 +0200
From:   Johannes Zink <j.zink@...gutronix.de>
To:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>,
        patchwork-jzi@...gutronix.de, kernel@...gutronix.de,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] drm/panel-simple: allow LVDS format override

Hi Dan,

do you have any input on this for me?

Best regards
Johannes

On 7/28/23 16:16, Johannes Zink wrote:
> Some panels support multiple LVDS data mapping formats, which can be
> used e.g. run displays on jeida-18 format when only 3 LVDS lanes are
> available.
> 
> Add parsing of an optional data-mapping devicetree property, which also
> touches up the bits per color to match the bus format.
> 
> Signed-off-by: Johannes Zink <j.zink@...gutronix.de>
> 
> ---
> 
> Changes:
> 
>    v3 -> v4: - worked in Dan's feedback (thanks for reviewing my work):
>                  - return with a proper error in case the call to
> 		  panel_simple_override_nondefault_lvds_datamapping()
> 		  fails
>                  - drop the unneeded and ambiguous ret variable
> 
>    v2 -> v3: - worked in Laurent's review findings (thanks for reviewing
>                my work):
> 	        - extract fixing up the bus format to separate
> 		  function
> 		- only call function on LVDS panels
> 		- fix typos found by Laurent
> 		- simplified error handling
> 
>    v1 -> v2: - fix missing unwind goto found by test robot
>                Reported-by: kernel test robot <lkp@...el.com>
>                Reported-by: Dan Carpenter <error27@...il.com>
>                Link: https://lore.kernel.org/r/202304160359.4LHmFOlU-lkp@intel.com/
> ---
>   drivers/gpu/drm/panel/panel-simple.c | 53 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 53 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 4badda6570d5..3a164931093e 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -40,6 +40,7 @@
>   #include <drm/drm_edid.h>
>   #include <drm/drm_mipi_dsi.h>
>   #include <drm/drm_panel.h>
> +#include <drm/drm_of.h>
>   
>   /**
>    * struct panel_desc - Describes a simple panel.
> @@ -549,6 +550,51 @@ static void panel_simple_parse_panel_timing_node(struct device *dev,
>   		dev_err(dev, "Reject override mode: No display_timing found\n");
>   }
>   
> +static int panel_simple_override_nondefault_lvds_datamapping(struct device *dev,
> +							     struct panel_simple *panel)
> +{
> +	int ret, bpc;
> +
> +	ret = drm_of_lvds_get_data_mapping(dev->of_node);
> +	if (ret < 0) {
> +		if (ret == -EINVAL)
> +			dev_warn(dev, "Ignore invalid data-mapping property\n");
> +
> +		/*
> +		 * Ignore non-existing or malformatted property, fallback to
> +		 * default data-mapping, and return 0.
> +		 */
> +		return 0;
> +	}
> +
> +	switch (ret) {
> +	default:
> +		WARN_ON(1);
> +		fallthrough;
> +	case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
> +		fallthrough;
> +	case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
> +		bpc = 8;
> +		break;
> +	case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
> +		bpc = 6;
> +	}
> +
> +	if (panel->desc->bpc != bpc || panel->desc->bus_format != ret) {
> +		struct panel_desc *override_desc;
> +
> +		override_desc = devm_kmemdup(dev, panel->desc, sizeof(*panel->desc), GFP_KERNEL);
> +		if (!override_desc)
> +			return -ENOMEM;
> +
> +		override_desc->bus_format = ret;
> +		override_desc->bpc = bpc;
> +		panel->desc = override_desc;
> +	}
> +
> +	return 0;
> +}
> +
>   static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>   {
>   	struct panel_simple *panel;
> @@ -601,6 +647,13 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>   			panel_simple_parse_panel_timing_node(dev, panel, &dt);
>   	}
>   
> +	if (desc->connector_type == DRM_MODE_CONNECTOR_LVDS) {
> +		/* Optional data-mapping property for overriding bus format */
> +		err = panel_simple_override_nondefault_lvds_datamapping(dev, panel);
> +		if (err)
> +			goto free_ddc;
> +	}
> +
>   	connector_type = desc->connector_type;
>   	/* Catch common mistakes for panels. */
>   	switch (connector_type) {
> 

-- 
Pengutronix e.K.                | Johannes Zink                  |
Steuerwalder Str. 21            | https://www.pengutronix.de/    |
31137 Hildesheim, Germany       | Phone: +49-5121-206917-0       |
Amtsgericht Hildesheim, HRA 2686| Fax:   +49-5121-206917-5555    |