linux-kernel - Re: [PATCH v2 3/3] drm/panel-simple: allow LVDS format override

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Message-ID: <20230602153938.GC3343@pendragon.ideasonboard.com>
Date:   Fri, 2 Jun 2023 18:39:38 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Johannes Zink <j.zink@...gutronix.de>
Cc:     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>,
        Thierry Reding <thierry.reding@...il.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>,
        patchwork-jzi@...gutronix.de, kernel@...gutronix.de,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] drm/panel-simple: allow LVDS format override

Hi Johannes,

Thank you for the patch.

On Tue, May 23, 2023 at 10:19:43AM +0200, 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.

Of course one could argue that the innolux,g101ice-l01 panel should have
used the panel-lvds bindings... :-)

> Signed-off-by: Johannes Zink <j.zink@...gutronix.de>
> 
> ---
> 
> Changes:
> 
>   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 | 39 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 38 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 2a9c1a785a5c..0a35fdb49ccb 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.
> @@ -559,7 +560,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>  	struct device_node *ddc;
>  	int connector_type;
>  	u32 bus_flags;
> -	int err;
> +	int err, ret;
>  
>  	panel = devm_kzalloc(dev, sizeof(*panel), GFP_KERNEL);
>  	if (!panel)
> @@ -605,6 +606,42 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>  			panel_simple_parse_panel_timing_node(dev, panel, &dt);
>  	}
>  
> +

Double blank line.

> +	/* optional data-mapping property for overriding bus format */

s/optional/Optional/

> +	ret = drm_of_lvds_get_data_mapping(dev->of_node);
> +	if (ret == -EINVAL) {
> +		dev_warn(dev, "Ignore invalid data-mapping property");
> +	} else if (ret != -ENODEV) {

If someone incorrectly sets the property in DT for a non-LVDS panel,
the result won't be nice. That's of course a DT issue, but I wonder if
we could/should protect against it. You could move this code to a
separate function (which would have the added benefit of lowering the
indentation level as you can return early in error cases), and call it
from panel_simple_probe() only if the panel is an LVDS panel (as
reported by its desc->bus_format value).

> +		int bpc;
> +
> +		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 (desc->bpc != bpc || desc->bus_format != ret) {
> +			struct panel_desc *override_desc;
> +
> +			override_desc = devm_kmemdup(dev, desc, sizeof(*desc), GFP_KERNEL);
> +			if (!override_desc) {
> +				err = -ENOMEM;
> +				goto free_ddc;
> +			}
> +
> +			override_desc->bus_format = ret;
> +			override_desc->bpc = bpc;
> +			panel->desc = override_desc;
> +		}
> +	}
> +
>  	connector_type = desc->connector_type;
>  	/* Catch common mistakes for panels. */
>  	switch (connector_type) {

-- 
Regards,

Laurent Pinchart