linux-kernel - Re: [PATCH 2/2] drm: lcdif: Add i.MX93 LCDIF support

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Date:   Mon, 23 Jan 2023 09:13:07 +0100
From:   Lothar Waßmann <LW@...O-electronics.de>
To:     Liu Ying <victor.liu@....com>
Cc:     dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        marex@...x.de, stefan@...er.ch, airlied@...il.com, daniel@...ll.ch,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com
Subject: Re: [PATCH 2/2] drm: lcdif: Add i.MX93 LCDIF support

Hi,

On Mon, 23 Jan 2023 15:23:58 +0800 Liu Ying wrote:
> The LCDIF embedded in i.MX93 SoC is essentially the same to those
> in i.MX8mp SoC.  However, i.MX93 LCDIF may connect with MIPI DSI
> controller through LCDIF cross line pattern(controlled by mediamix
> blk-ctrl) or connect with LVDS display bridge(LDB) directly or a
> parallel display(also through mediamix blk-ctrl), so add multiple
> encoders(with DRM_MODE_ENCODER_NONE encoder type) support in the
> LCDIF DRM driver and find a bridge to attach the relevant encoder's
> chain when needed.  While at it, derive lcdif_crtc_state structure
> from drm_crtc_state structure to introduce bus_format and bus_flags
> states so that the next downstream bridges may use consistent bus
> format and bus flags.
> 
> Signed-off-by: Liu Ying <victor.liu@....com>
> ---
>  drivers/gpu/drm/mxsfb/lcdif_drv.c |  73 +++++++++--
>  drivers/gpu/drm/mxsfb/lcdif_drv.h |   6 +-
>  drivers/gpu/drm/mxsfb/lcdif_kms.c | 206 ++++++++++++++++++++----------
>  3 files changed, 208 insertions(+), 77 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/lcdif_drv.c b/drivers/gpu/drm/mxsfb/lcdif_drv.c
> index cc2ceb301b96..4d41f6b6eb14 100644
> --- a/drivers/gpu/drm/mxsfb/lcdif_drv.c
> +++ b/drivers/gpu/drm/mxsfb/lcdif_drv.c
> @@ -9,13 +9,16 @@
>  #include <linux/dma-mapping.h>
>  #include <linux/io.h>
>  #include <linux/module.h>
> +#include <linux/of.h>
>  #include <linux/of_device.h>
> +#include <linux/of_graph.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
>  
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_bridge.h>
>  #include <drm/drm_drv.h>
> +#include <drm/drm_encoder.h>
>  #include <drm/drm_fbdev_generic.h>
>  #include <drm/drm_gem_dma_helper.h>
>  #include <drm/drm_gem_framebuffer_helper.h>
> @@ -38,21 +41,70 @@ static const struct drm_mode_config_helper_funcs lcdif_mode_config_helpers = {
>  	.atomic_commit_tail = drm_atomic_helper_commit_tail_rpm,
>  };
>  
> +static const struct drm_encoder_funcs lcdif_encoder_funcs = {
> +	.destroy = drm_encoder_cleanup,
> +};
> +
>  static int lcdif_attach_bridge(struct lcdif_drm_private *lcdif)
>  {
> -	struct drm_device *drm = lcdif->drm;
> +	struct device *dev = lcdif->drm->dev;
> +	struct device_node *ep;
>  	struct drm_bridge *bridge;
>  	int ret;
>  
> -	bridge = devm_drm_of_get_bridge(drm->dev, drm->dev->of_node, 0, 0);
> -	if (IS_ERR(bridge))
> -		return PTR_ERR(bridge);
> -
> -	ret = drm_bridge_attach(&lcdif->encoder, bridge, NULL, 0);
> -	if (ret)
> -		return dev_err_probe(drm->dev, ret, "Failed to attach bridge\n");
> -
> -	lcdif->bridge = bridge;
> +	for_each_endpoint_of_node(dev->of_node, ep) {
> +		struct device_node *remote;
> +		struct of_endpoint of_ep;
> +		struct drm_encoder *encoder;
> +
> +		remote = of_graph_get_remote_port_parent(ep);
> +		if (!remote || !of_device_is_available(remote)) {
'!remote ||' is redundant, since of_device_is_available already checks
for a NULL pointer.

[...]

> diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> index 262bc43b1079..ba36447ed900 100644
> --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
> +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
[...]
> @@ -529,6 +580,46 @@ static void lcdif_crtc_atomic_disable(struct drm_crtc *crtc,
>  	pm_runtime_put_sync(drm->dev);
>  }
>  
> +static void lcdif_crtc_reset(struct drm_crtc *crtc)
> +{
> +	struct lcdif_crtc_state *state;
> +
> +	if (crtc->state)
> +		__drm_atomic_helper_crtc_destroy_state(crtc->state);
> +
> +	kfree(to_lcdif_crtc_state(crtc->state));
>
If crtc-state can be NULL at this point, this will only work as long as
'base' is the first member of the lcdif_crtc_state struct (which
currently is the case, but there is no guarantee that this will always
be this way), otherwise the if clause above is not needed.



Lothar Waßmann