Date:   Wed, 18 Apr 2018 09:29:48 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Sean Paul <seanpaul@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 4/6] drm/atmel-hlcdc: support bus-width (12/16/18/24)
 in endpoint nodes

On Tue, 17 Apr 2018 15:10:50 +0200
Peter Rosin <peda@...ntia.se> wrote:

> This beats the heuristic that the connector is involved in what format
> should be output for cases where this fails.
> 
> E.g. if there is a bridge that changes format between the encoder and the
> connector, or if some of the RGB pins between the lcd controller and the
> encoder are not routed on the PCB.
> 
> This is critical for the devices that have the "conflicting output
> formats" issue (SAM9N12, SAM9X5, SAMA5D3), since the most significant
> RGB bits move around depending on the selected output mode. For
> devices that do not have the "conflicting output formats" issue
> (SAMA5D2, SAMA5D4), this is completely irrelevant.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 85 ++++++++++++++++++++------
>  1 file changed, 65 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> index d73281095fac..2e718959981e 100644
> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> @@ -19,12 +19,14 @@
>   */
>  
>  #include <linux/clk.h>
> +#include <linux/of_graph.h>
>  #include <linux/pm.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/pinctrl/consumer.h>
>  
>  #include <drm/drm_crtc.h>
>  #include <drm/drm_crtc_helper.h>
> +#include <drm/drm_of.h>
>  #include <drm/drmP.h>
>  
>  #include <video/videomode.h>
> @@ -226,6 +228,68 @@ static void atmel_hlcdc_crtc_atomic_enable(struct drm_crtc *c,
>  #define ATMEL_HLCDC_RGB888_OUTPUT	BIT(3)
>  #define ATMEL_HLCDC_OUTPUT_MODE_MASK	GENMASK(3, 0)
>  
> +static int atmel_hlcdc_connector_output_mode(struct drm_connector_state *state)
> +{
> +	struct drm_connector *connector = state->connector;
> +	struct drm_display_info *info = &connector->display_info;
> +	unsigned int supported_fmts = 0;
> +	struct device_node *ep;
> +	int j;
> +
> +	/*
> +	 * Use the connector index as an approximation of the
> +	 * endpoint node index. We know it's true for our case
> +	 * depending on the driver implementation.
> +	 */
> +	ep = of_graph_get_endpoint_by_regs(connector->dev->dev->of_node, 0,
> +					   connector->index);
> +

Hm, this sounds a bit fragile. Can't we have a reference to the of_node
attached to the connector? Or maybe we can parse this earlier and set a
constraint on the accepted modes.

> +	if (ep) {
> +		int bus_fmt = drm_of_media_bus_fmt(ep);

Hm, you're extracting this piece of information from the DT every time
an atomic modeset is done. I'd really prefer to have this done once at
probe time. Since this property is attached to the connector, maybe we
should overwrite the info->bus_formats[] array or mark some of its
entries as invalid.

> +
> +		of_node_put(ep);
> +
> +		if (bus_fmt < 0)
> +			return bus_fmt;
> +
> +		switch (bus_fmt) {
> +		case 0:
> +			break;
> +		case MEDIA_BUS_FMT_RGB444_1X12:
> +			return ATMEL_HLCDC_RGB444_OUTPUT;
> +		case MEDIA_BUS_FMT_RGB565_1X16:
> +			return ATMEL_HLCDC_RGB565_OUTPUT;
> +		case MEDIA_BUS_FMT_RGB666_1X18:
> +			return ATMEL_HLCDC_RGB666_OUTPUT;
> +		case MEDIA_BUS_FMT_RGB888_1X24:
> +			return ATMEL_HLCDC_RGB888_OUTPUT;
> +		default:
> +			return -EINVAL;
> +		}
> +	}
> +
> +	for (j = 0; j < info->num_bus_formats; j++) {
> +		switch (info->bus_formats[j]) {
> +		case MEDIA_BUS_FMT_RGB444_1X12:
> +			supported_fmts |= ATMEL_HLCDC_RGB444_OUTPUT;
> +			break;
> +		case MEDIA_BUS_FMT_RGB565_1X16:
> +			supported_fmts |= ATMEL_HLCDC_RGB565_OUTPUT;
> +			break;
> +		case MEDIA_BUS_FMT_RGB666_1X18:
> +			supported_fmts |= ATMEL_HLCDC_RGB666_OUTPUT;
> +			break;
> +		case MEDIA_BUS_FMT_RGB888_1X24:
> +			supported_fmts |= ATMEL_HLCDC_RGB888_OUTPUT;
> +			break;
> +		default:
> +			break;
> +		}
> +	}
> +
> +	return supported_fmts;
> +}
> +
>  static int atmel_hlcdc_crtc_select_output_mode(struct drm_crtc_state *state)
>  {
>  	unsigned int output_fmts = ATMEL_HLCDC_OUTPUT_MODE_MASK;
> @@ -238,31 +302,12 @@ static int atmel_hlcdc_crtc_select_output_mode(struct drm_crtc_state *state)
>  	crtc = drm_crtc_to_atmel_hlcdc_crtc(state->crtc);
>  
>  	for_each_new_connector_in_state(state->state, connector, cstate, i) {
> -		struct drm_display_info *info = &connector->display_info;
>  		unsigned int supported_fmts = 0;
> -		int j;
>  
>  		if (!cstate->crtc)
>  			continue;
>  
> -		for (j = 0; j < info->num_bus_formats; j++) {
> -			switch (info->bus_formats[j]) {
> -			case MEDIA_BUS_FMT_RGB444_1X12:
> -				supported_fmts |= ATMEL_HLCDC_RGB444_OUTPUT;
> -				break;
> -			case MEDIA_BUS_FMT_RGB565_1X16:
> -				supported_fmts |= ATMEL_HLCDC_RGB565_OUTPUT;
> -				break;
> -			case MEDIA_BUS_FMT_RGB666_1X18:
> -				supported_fmts |= ATMEL_HLCDC_RGB666_OUTPUT;
> -				break;
> -			case MEDIA_BUS_FMT_RGB888_1X24:
> -				supported_fmts |= ATMEL_HLCDC_RGB888_OUTPUT;
> -				break;
> -			default:
> -				break;
> -			}
> -		}
> +		supported_fmts = atmel_hlcdc_connector_output_mode(cstate);
>  
>  		if (crtc->dc->desc->conflicting_output_formats)
>  			output_fmts &= supported_fmts;

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