Re: [PATCH 8/8] drm: mxsfb: Add support for the bus-width DT property

[Sam Ravnborg <sam@ravnborg.org>]

Hi Laurent.

On Thu, Aug 13, 2020 at 04:29:10AM +0300, Laurent Pinchart wrote:
> A new bus-width DT property has been introduced in the bindings to allow
> overriding the bus width. Support it.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

We already reads the bus-width in following files in drm:
atmel-hlcdc/atmel_hlcdc_output.c bridge/ti-tfp410.c

So this calls for a common helper to do this like:

int drm_of_bus_fmt(const struct device_node *ep)
{
}

This helper could then read bus-width, data-shift (if relevant)
and return the relevant bus format.

I can see that bridge/ti-tfp410.c assumes 12 equals
MEDIA_BUS_FMT_RGB888_2X12_LE where as mxsfb assumes 12 is
MEDIA_BUS_FMT_RGB444_1X12.
I do not know why neither how to handle this difference.
Maybe this is something to do with DVI as this is what tfp410
seems to support.

	Sam


> ---
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 26 ++++++++++++++++++++++++++
>  drivers/gpu/drm/mxsfb/mxsfb_drv.h |  2 ++
>  drivers/gpu/drm/mxsfb/mxsfb_kms.c |  8 ++++++--
>  3 files changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index 8c549c3931af..fab3aae8cf73 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -95,10 +95,36 @@ static int mxsfb_attach_bridge(struct mxsfb_drm_private *mxsfb)
>  {
>  	struct drm_device *drm = mxsfb->drm;
>  	struct drm_connector_list_iter iter;
> +	struct device_node *ep;
>  	struct drm_panel *panel;
>  	struct drm_bridge *bridge;
> +	u32 bus_width = 0;
>  	int ret;
>  
> +	ep = of_graph_get_endpoint_by_regs(drm->dev->of_node, 0, 0);
> +	if (!ep)
> +		return -ENODEV;
> +
> +	of_property_read_u32(ep, "bus-width", &bus_width);
> +	of_node_put(ep);
> +
> +	switch (bus_width) {
> +	case 16:
> +		mxsfb->bus_format = MEDIA_BUS_FMT_RGB565_1X16;
> +		break;
> +	case 18:
> +		mxsfb->bus_format = MEDIA_BUS_FMT_RGB666_1X18;
> +		break;
> +	case 24:
> +		mxsfb->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> +		break;
> +	case 0:
> +		break;
> +	default:
> +		DRM_DEV_ERROR(drm->dev, "Invalid bus-width %u", bus_width);
> +		return -ENODEV;
> +	}
> +
>  	ret = drm_of_find_panel_or_bridge(drm->dev->of_node, 0, 0, &panel,
>  					  &bridge);
>  	if (ret)
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.h b/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> index 399d23e91ed1..c4f7a8a0c891 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> @@ -32,6 +32,8 @@ struct mxsfb_drm_private {
>  	struct clk			*clk_axi;
>  	struct clk			*clk_disp_axi;
>  
> +	u32				bus_format;
> +
>  	struct drm_device		*drm;
>  	struct {
>  		struct drm_plane	primary;
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> index b721b8b262ce..6d512f346918 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> @@ -50,11 +50,15 @@ static void mxsfb_set_formats(struct mxsfb_drm_private *mxsfb)
>  {
>  	struct drm_device *drm = mxsfb->drm;
>  	const u32 format = mxsfb->crtc.primary->state->fb->format->format;
> -	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> +	u32 bus_format;
>  	u32 ctrl, ctrl1;
>  
> -	if (mxsfb->connector->display_info.num_bus_formats)
> +	if (mxsfb->bus_format)
> +		bus_format = mxsfb->bus_format;
> +	else if (mxsfb->connector->display_info.num_bus_formats)
>  		bus_format = mxsfb->connector->display_info.bus_formats[0];
> +	else
> +		bus_format = MEDIA_BUS_FMT_RGB888_1X24;
>  
>  	DRM_DEV_DEBUG_DRIVER(drm->dev, "Using bus_format: 0x%08X\n",
>  			     bus_format);
> -- 
> Regards,
> 
> Laurent Pinchart
> 
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