linux-kernel - Re: [PATCH v3 4/4] drm/panel: simple: add bus-format support for panel-dpi

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Date:   Wed, 3 Aug 2022 12:15:12 +0530
From:   Aradhya Bhatia <a-bhatia1@...com>
To:     Max Krummenacher <max.oss.09@...il.com>,
        <max.krummenacher@...adex.com>
CC:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh@...nel.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Maxime Ripard <mripard@...nel.org>,
        Marek Vasut <marex@...x.de>,
        Christoph Niedermaier <cniedermaier@...electronics.com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Sam Ravnborg <sam@...nborg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] drm/panel: simple: add bus-format support for
 panel-dpi



On 28-Jun-22 23:48, Max Krummenacher wrote:
> From: Max Krummenacher <max.krummenacher@...adex.com>
> 
> Evaluate the device tree bus-format property to set bus_format for
> a 'panel-dpi' panel. Additionally infer the bpc value from the
> given bus-format.
> 
> Valid values for bus-format are found in:
> <include/dt-bindings/display/dt-media-bus-format.h>
> 
> This completes the addition of panel-dpi to completely specify
> a panel-simple panel from the device tree.
> 
> Signed-off-by: Max Krummenacher <max.krummenacher@...adex.com>
> 
> ---
> 
> Changes in v3:
> - Moved the bus-format property under the port/endpoint node as
>    suggested by Rob Herring
> 
> Changes in v2:
> - Fix errors found by dt_binding_check
> 
>   drivers/gpu/drm/panel/panel-simple.c | 49 ++++++++++++++++++++++++++++
>   1 file changed, 49 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 4a2e580a2f7b..f1a457f1069e 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -21,9 +21,11 @@
>    * DEALINGS IN THE SOFTWARE.
>    */
>   
> +#include <dt-bindings/display/dt-media-bus-format.h>
>   #include <linux/delay.h>
>   #include <linux/gpio/consumer.h>
>   #include <linux/module.h>
> +#include <linux/of_graph.h>
>   #include <linux/of_platform.h>
>   #include <linux/platform_device.h>
>   #include <linux/pm_runtime.h>
> @@ -449,10 +451,12 @@ static int panel_dpi_probe(struct device *dev,
>   			   struct panel_simple *panel)
>   {
>   	struct display_timing *timing;
> +	struct device_node *endpoint;
>   	const struct device_node *np;
>   	struct panel_desc *desc;
>   	unsigned int bus_flags;
>   	struct videomode vm;
> +	u32 bus_format;
>   	int ret;
>   
>   	np = dev->of_node;
> @@ -477,6 +481,51 @@ static int panel_dpi_probe(struct device *dev,
>   	of_property_read_u32(np, "width-mm", &desc->size.width);
>   	of_property_read_u32(np, "height-mm", &desc->size.height);
>   
> +	endpoint = of_graph_get_endpoint_by_regs(np, -1, -1);
> +	if (endpoint &&
> +	    !of_property_read_u32(endpoint, "bus-format", &bus_format)) {
> +		/* infer bpc from bus-format */
> +		switch (bus_format) {
> +		case DT_MEDIA_BUS_FMT_RGB565_1X16:
> +			desc->bus_format = MEDIA_BUS_FMT_RGB565_1X16;
> +			desc->bpc = 6;
> +			break;
> +		case DT_MEDIA_BUS_FMT_RGB666_1X18:
> +			desc->bus_format = MEDIA_BUS_FMT_RGB666_1X18;
> +			desc->bpc = 6;
> +			break;
> +		case DT_MEDIA_BUS_FMT_RGB666_1X24_CPADHI:
> +			desc->bus_format = MEDIA_BUS_FMT_RGB666_1X24_CPADHI;
> +			desc->bpc = 6;
> +			break;
> +		case DT_MEDIA_BUS_FMT_BGR888_1X24:
> +			desc->bus_format = MEDIA_BUS_FMT_BGR888_1X24;
> +			desc->bpc = 8;
> +			break;
> +		case DT_MEDIA_BUS_FMT_GBR888_1X24:
> +			desc->bus_format = MEDIA_BUS_FMT_GBR888_1X24;
> +			desc->bpc = 8;
> +			break;
> +		case DT_MEDIA_BUS_FMT_RBG888_1X24:
> +			desc->bus_format = MEDIA_BUS_FMT_RBG888_1X24;
> +			desc->bpc = 8;
> +			break;
> +		case DT_MEDIA_BUS_FMT_RGB888_1X24:
> +			desc->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> +			desc->bpc = 8;
> +			break;
> +		case DT_MEDIA_BUS_FMT_RGB888_1X32_PADHI:
> +			desc->bus_format = MEDIA_BUS_FMT_RGB888_1X32_PADHI;
> +			desc->bpc = 8;
> +			break;
> +		default:
> +			dev_err(dev, "%pOF: unknown bus-format property\n", np);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	of_node_put(endpoint);
> +
>   	/* Extract bus_flags from display_timing */
>   	bus_flags = 0;
>   	vm.flags = timing->flags;

I understand that it is important to add a bus-format property for dumb
dpi-panels, and I agree with the implementation in the patch-set.

However,
I do not yet fully understand Rob's comments on the dt-bindings side of
patch set (patch 1/4) and what consequences it may cause if that remains
unresolved.

Given that the bus-format property gets added, I do not see any concern
with the panel-simple driver patch.


Reviewed-by: Aradhya Bhatia <a-bhatia1@...com>


Regards
Aradhya