Re: [PATCH 02/21] drm: mxsfb: Use drm_panel_bridge

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On 2020-03-09 20:51, Laurent Pinchart wrote:
> Replace the manual connector implementation based on drm_panel with the
> drm_panel_bridge helper. This simplifies the mxsfb driver by removing
> connector-related code, and standardizing all pipeline control
> operations on bridges.
> 
> A hack is needed to get hold of the connector, as that's our only source
> of bus flags and formats for now. As soon as the bridge API provides us
> with that information this can be fixed.

This seems like a nice simplification.

I gave this a go applied on today's drm-misc-next using a Colibri iMX7
(imx7d-colibri-emmc-eval-v3.dts device tree). This device makes use of
the simple panel driver. I get this when booting:

[    2.976698] [drm] Supports vblank timestamp caching Rev 2
(21.10.2013).
[    2.983526] ------------[ cut here ]------------
[    2.988180] WARNING: CPU: 0 PID: 1 at
drivers/gpu/drm/bridge/panel.c:267 devm_drm_panel_bridge_add+0x25/0x28
[    2.998059] Modules linked in:
[    3.001159] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
5.6.0-rc5-yocto-standard-01250-ga4ce5db7c9f1 #29
[    3.010493] Hardware name: Freescale i.MX7 Dual (Device Tree)
[    3.016281] [<c010f089>] (unwind_backtrace) from [<c010a9bb>]
(show_stack+0xb/0xc)
[    3.023887] [<c010a9bb>] (show_stack) from [<c08b33cf>]
(dump_stack+0x63/0x70)
[    3.031144] [<c08b33cf>] (dump_stack) from [<c0124385>]
(__warn+0x9d/0xb0)
[    3.038047] [<c0124385>] (__warn) from [<c0124403>]
(warn_slowpath_fmt+0x6b/0x70)
[    3.045564] [<c0124403>] (warn_slowpath_fmt) from [<c04ebf65>]
(devm_drm_panel_bridge_add+0x25/0x28)
[    3.054736] [<c04ebf65>] (devm_drm_panel_bridge_add) from
[<c051fe7f>] (mxsfb_probe+0x197/0x2e0)
[    3.063559] [<c051fe7f>] (mxsfb_probe) from [<c0532e91>]
(platform_drv_probe+0x2d/0x60)
[    3.071598] [<c0532e91>] (platform_drv_probe) from [<c0531615>]
(really_probe+0x1dd/0x330)
[    3.079897] [<c0531615>] (really_probe) from [<c05318b3>]
(driver_probe_device+0x4f/0x154)
[    3.088195] [<c05318b3>] (driver_probe_device) from [<c0531b3f>]
(device_driver_attach+0x37/0x44)
[    3.097101] [<c0531b3f>] (device_driver_attach) from [<c0531bc7>]
(__driver_attach+0x7b/0xec)
[    3.105660] [<c0531bc7>] (__driver_attach) from [<c0530069>]
(bus_for_each_dev+0x3d/0x64)
[    3.113870] [<c0530069>] (bus_for_each_dev) from [<c0530b9b>]
(bus_add_driver+0xef/0x160)
[    3.122081] [<c0530b9b>] (bus_add_driver) from [<c053238d>]
(driver_register+0x35/0x9c)
[    3.130119] [<c053238d>] (driver_register) from [<c0102de9>]
(do_one_initcall+0x3d/0x1e4)
[    3.138333] [<c0102de9>] (do_one_initcall) from [<c1100d13>]
(kernel_init_freeable+0x1b3/0x1fc)
[    3.147069] [<c1100d13>] (kernel_init_freeable) from [<c08c3f7b>]
(kernel_init+0x7/0xd0)
[    3.155194] [<c08c3f7b>] (kernel_init) from [<c01010f9>]
(ret_from_fork+0x11/0x38)
[    3.162789] Exception stack(0xec0e3fb0 to 0xec0e3ff8)
[    3.167862] 3fa0:                                     00000000
00000000 00000000 00000000
[    3.176071] 3fc0: 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000
[    3.184278] 3fe0: 00000000 00000000 00000000 00000000 00000013
00000000
[    3.191029] ---[ end trace b69e1f44de470959 ]---
[    3.195671] mxsfb 30730000.lcdif: Cannot connect bridge: -19

Should we maybe use devm_drm_panel_bridge_add_typed?

Two more comments below.

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/mxsfb/Makefile    |   2 +-
>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 105 ++++++++++++++----------------
>  drivers/gpu/drm/mxsfb/mxsfb_drv.h |   5 +-
>  drivers/gpu/drm/mxsfb/mxsfb_out.c |  99 ----------------------------
>  4 files changed, 53 insertions(+), 158 deletions(-)
>  delete mode 100644 drivers/gpu/drm/mxsfb/mxsfb_out.c
> 
> diff --git a/drivers/gpu/drm/mxsfb/Makefile b/drivers/gpu/drm/mxsfb/Makefile
> index ff6e358088fa..811584e54ad1 100644
> --- a/drivers/gpu/drm/mxsfb/Makefile
> +++ b/drivers/gpu/drm/mxsfb/Makefile
> @@ -1,3 +1,3 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -mxsfb-y := mxsfb_drv.o mxsfb_crtc.o mxsfb_out.o
> +mxsfb-y := mxsfb_drv.o mxsfb_crtc.o
>  obj-$(CONFIG_DRM_MXSFB)	+= mxsfb.o
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> index 2e6068d96034..cffc70257bd3 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> @@ -29,7 +29,6 @@
>  #include <drm/drm_gem_framebuffer_helper.h>
>  #include <drm/drm_irq.h>
>  #include <drm/drm_of.h>
> -#include <drm/drm_panel.h>
>  #include <drm/drm_probe_helper.h>
>  #include <drm/drm_simple_kms_helper.h>
>  #include <drm/drm_vblank.h>
> @@ -100,29 +99,11 @@ static void mxsfb_pipe_enable(struct
> drm_simple_display_pipe *pipe,
>  			      struct drm_crtc_state *crtc_state,
>  			      struct drm_plane_state *plane_state)
>  {
> -	struct drm_connector *connector;
>  	struct mxsfb_drm_private *mxsfb = drm_pipe_to_mxsfb_drm_private(pipe);
>  	struct drm_device *drm = pipe->plane.dev;
>  
> -	if (!mxsfb->connector) {
> -		list_for_each_entry(connector,
> -				    &drm->mode_config.connector_list,
> -				    head)
> -			if (connector->encoder == &mxsfb->pipe.encoder) {
> -				mxsfb->connector = connector;
> -				break;
> -			}
> -	}
> -
> -	if (!mxsfb->connector) {
> -		dev_warn(drm->dev, "No connector attached, using default\n");
> -		mxsfb->connector = &mxsfb->panel_connector;
> -	}
> -
>  	pm_runtime_get_sync(drm->dev);
> -	drm_panel_prepare(mxsfb->panel);
>  	mxsfb_crtc_enable(mxsfb);
> -	drm_panel_enable(mxsfb->panel);
>  }
>  
>  static void mxsfb_pipe_disable(struct drm_simple_display_pipe *pipe)
> @@ -132,9 +113,7 @@ static void mxsfb_pipe_disable(struct
> drm_simple_display_pipe *pipe)
>  	struct drm_crtc *crtc = &pipe->crtc;
>  	struct drm_pending_vblank_event *event;
>  
> -	drm_panel_disable(mxsfb->panel);
>  	mxsfb_crtc_disable(mxsfb);
> -	drm_panel_unprepare(mxsfb->panel);
>  	pm_runtime_put_sync(drm->dev);
>  
>  	spin_lock_irq(&drm->event_lock);
> @@ -144,9 +123,6 @@ static void mxsfb_pipe_disable(struct
> drm_simple_display_pipe *pipe)
>  		drm_crtc_send_vblank_event(crtc, event);
>  	}
>  	spin_unlock_irq(&drm->event_lock);
> -
> -	if (mxsfb->connector != &mxsfb->panel_connector)
> -		mxsfb->connector = NULL;
>  }
>  
>  static void mxsfb_pipe_update(struct drm_simple_display_pipe *pipe,
> @@ -190,6 +166,48 @@ static struct drm_simple_display_pipe_funcs mxsfb_funcs = {
>  	.disable_vblank	= mxsfb_pipe_disable_vblank,
>  };
>  
> +static int mxsfb_attach_bridge(struct mxsfb_drm_private *mxsfb)
> +{
> +	struct drm_device *drm = mxsfb->drm;
> +	struct drm_connector_list_iter iter;
> +	struct drm_panel *panel;
> +	struct drm_bridge *bridge;
> +	int ret;
> +
> +	ret = drm_of_find_panel_or_bridge(drm->dev->of_node, 0, 0, &panel,
> +					  &bridge);
> +	if (ret)
> +		return ret;
> +
> +	if (panel) {
> +		bridge = devm_drm_panel_bridge_add(drm->dev, panel);

Do we need a select DRM_PANEL_BRIDGE in Kconfig maybe? From what I can
tell there is no devm_drm_panel_bridge_add() stub if DRM_PANEL_BRIDGE is
not selected.

> +		if (IS_ERR(bridge))
> +			return PTR_ERR(bridge);
> +	}
> +
> +	if (!bridge)
> +		return -ENODEV;
> +
> +	ret = drm_simple_display_pipe_attach_bridge(&mxsfb->pipe, bridge);
> +	if (ret) {
> +		DRM_DEV_ERROR(drm->dev,
> +			      "failed to attach bridge: %d\n", ret);
> +		return ret;
> +	}
> +
> +	mxsfb->bridge = bridge;
> +
> +	/*
> +	 * Get hold of the connector. This is a bit of a hack, until the bridge
> +	 * API gives us bus flags and formats.
> +	 */
> +	drm_connector_list_iter_begin(drm, &iter);
> +	mxsfb->connector = drm_connector_list_iter_next(&iter);
> +	drm_connector_list_iter_end(&iter);

Could we not just use drm_panel_bridge_connector() here?

--
Stefan

> +
> +	return 0;
> +}
> +
>  static int mxsfb_load(struct drm_device *drm, unsigned long flags)
>  {
>  	struct platform_device *pdev = to_platform_device(drm->dev);
> @@ -201,6 +219,7 @@ static int mxsfb_load(struct drm_device *drm,
> unsigned long flags)
>  	if (!mxsfb)
>  		return -ENOMEM;
>  
> +	mxsfb->drm = drm;
>  	drm->dev_private = mxsfb;
>  	mxsfb->devdata = &mxsfb_devdata[pdev->id_entry->driver_data];
>  
> @@ -236,41 +255,17 @@ static int mxsfb_load(struct drm_device *drm,
> unsigned long flags)
>  	/* Modeset init */
>  	drm_mode_config_init(drm);
>  
> -	ret = mxsfb_create_output(drm);
> -	if (ret < 0) {
> -		dev_err(drm->dev, "Failed to create outputs\n");
> -		goto err_vblank;
> -	}
> -
>  	ret = drm_simple_display_pipe_init(drm, &mxsfb->pipe, &mxsfb_funcs,
> -			mxsfb_formats, ARRAY_SIZE(mxsfb_formats), NULL,
> -			mxsfb->connector);
> +			mxsfb_formats, ARRAY_SIZE(mxsfb_formats), NULL, NULL);
>  	if (ret < 0) {
>  		dev_err(drm->dev, "Cannot setup simple display pipe\n");
>  		goto err_vblank;
>  	}
>  
> -	/*
> -	 * Attach panel only if there is one.
> -	 * If there is no panel attach, it must be a bridge. In this case, we
> -	 * need a reference to its connector for a proper initialization.
> -	 * We will do this check in pipe->enable(), since the connector won't
> -	 * be attached to an encoder until then.
> -	 */
> -
> -	if (mxsfb->panel) {
> -		ret = drm_panel_attach(mxsfb->panel, mxsfb->connector);
> -		if (ret) {
> -			dev_err(drm->dev, "Cannot connect panel: %d\n", ret);
> -			goto err_vblank;
> -		}
> -	} else if (mxsfb->bridge) {
> -		ret = drm_simple_display_pipe_attach_bridge(&mxsfb->pipe,
> -							    mxsfb->bridge);
> -		if (ret) {
> -			dev_err(drm->dev, "Cannot connect bridge: %d\n", ret);
> -			goto err_vblank;
> -		}
> +	ret = mxsfb_attach_bridge(mxsfb);
> +	if (ret) {
> +		dev_err(drm->dev, "Cannot connect bridge: %d\n", ret);
> +		goto err_vblank;
>  	}
>  
>  	drm->mode_config.min_width	= MXSFB_MIN_XRES;
> @@ -288,7 +283,7 @@ static int mxsfb_load(struct drm_device *drm,
> unsigned long flags)
>  
>  	if (ret < 0) {
>  		dev_err(drm->dev, "Failed to install IRQ handler\n");
> -		goto err_irq;
> +		goto err_vblank;
>  	}
>  
>  	drm_kms_helper_poll_init(drm);
> @@ -299,8 +294,6 @@ static int mxsfb_load(struct drm_device *drm,
> unsigned long flags)
>  
>  	return 0;
>  
> -err_irq:
> -	drm_panel_detach(mxsfb->panel);
>  err_vblank:
>  	pm_runtime_disable(drm->dev);
>  
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> b/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> index 0b65b5194a9c..0e3e5a63bbf9 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.h
> @@ -8,6 +8,8 @@
>  #ifndef __MXSFB_DRV_H__
>  #define __MXSFB_DRV_H__
>  
> +struct drm_device;
> +
>  struct mxsfb_devdata {
>  	unsigned int	 transfer_count;
>  	unsigned int	 cur_buf;
> @@ -26,10 +28,9 @@ struct mxsfb_drm_private {
>  	struct clk			*clk_axi;
>  	struct clk			*clk_disp_axi;
>  
> +	struct drm_device		*drm;
>  	struct drm_simple_display_pipe	pipe;
> -	struct drm_connector		panel_connector;
>  	struct drm_connector		*connector;
> -	struct drm_panel		*panel;
>  	struct drm_bridge		*bridge;
>  };
>  
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_out.c
> b/drivers/gpu/drm/mxsfb/mxsfb_out.c
> deleted file mode 100644
> index 9eca1605d11d..000000000000
> --- a/drivers/gpu/drm/mxsfb/mxsfb_out.c
> +++ /dev/null
> @@ -1,99 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-or-later
> -/*
> - * Copyright (C) 2016 Marek Vasut <marex@xxxxxxx>
> - */
> -
> -#include <linux/of_graph.h>
> -
> -#include <drm/drm_atomic.h>
> -#include <drm/drm_atomic_helper.h>
> -#include <drm/drm_crtc.h>
> -#include <drm/drm_fb_cma_helper.h>
> -#include <drm/drm_gem_cma_helper.h>
> -#include <drm/drm_of.h>
> -#include <drm/drm_panel.h>
> -#include <drm/drm_plane_helper.h>
> -#include <drm/drm_probe_helper.h>
> -#include <drm/drm_simple_kms_helper.h>
> -
> -#include "mxsfb_drv.h"
> -
> -static struct mxsfb_drm_private *
> -drm_connector_to_mxsfb_drm_private(struct drm_connector *connector)
> -{
> -	return container_of(connector, struct mxsfb_drm_private,
> -			    panel_connector);
> -}
> -
> -static int mxsfb_panel_get_modes(struct drm_connector *connector)
> -{
> -	struct mxsfb_drm_private *mxsfb =
> -			drm_connector_to_mxsfb_drm_private(connector);
> -
> -	if (mxsfb->panel)
> -		return drm_panel_get_modes(mxsfb->panel, connector);
> -
> -	return 0;
> -}
> -
> -static const struct
> -drm_connector_helper_funcs mxsfb_panel_connector_helper_funcs = {
> -	.get_modes = mxsfb_panel_get_modes,
> -};
> -
> -static enum drm_connector_status
> -mxsfb_panel_connector_detect(struct drm_connector *connector, bool force)
> -{
> -	struct mxsfb_drm_private *mxsfb =
> -			drm_connector_to_mxsfb_drm_private(connector);
> -
> -	if (mxsfb->panel)
> -		return connector_status_connected;
> -
> -	return connector_status_disconnected;
> -}
> -
> -static void mxsfb_panel_connector_destroy(struct drm_connector *connector)
> -{
> -	struct mxsfb_drm_private *mxsfb =
> -			drm_connector_to_mxsfb_drm_private(connector);
> -
> -	if (mxsfb->panel)
> -		drm_panel_detach(mxsfb->panel);
> -
> -	drm_connector_unregister(connector);
> -	drm_connector_cleanup(connector);
> -}
> -
> -static const struct drm_connector_funcs mxsfb_panel_connector_funcs = {
> -	.detect			= mxsfb_panel_connector_detect,
> -	.fill_modes		= drm_helper_probe_single_connector_modes,
> -	.destroy		= mxsfb_panel_connector_destroy,
> -	.reset			= drm_atomic_helper_connector_reset,
> -	.atomic_duplicate_state	= drm_atomic_helper_connector_duplicate_state,
> -	.atomic_destroy_state	= drm_atomic_helper_connector_destroy_state,
> -};
> -
> -int mxsfb_create_output(struct drm_device *drm)
> -{
> -	struct mxsfb_drm_private *mxsfb = drm->dev_private;
> -	int ret;
> -
> -	ret = drm_of_find_panel_or_bridge(drm->dev->of_node, 0, 0,
> -					  &mxsfb->panel, &mxsfb->bridge);
> -	if (ret)
> -		return ret;
> -
> -	if (mxsfb->panel) {
> -		mxsfb->connector = &mxsfb->panel_connector;
> -		mxsfb->connector->dpms = DRM_MODE_DPMS_OFF;
> -		mxsfb->connector->polled = 0;
> -		drm_connector_helper_add(mxsfb->connector,
> -					 &mxsfb_panel_connector_helper_funcs);
> -		ret = drm_connector_init(drm, mxsfb->connector,
> -					 &mxsfb_panel_connector_funcs,
> -					 DRM_MODE_CONNECTOR_Unknown);
> -	}
> -
> -	return ret;
> -}
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