Re: [PATCH 3/4] drm: Introduce drm_fb_helper_prepare()

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On Tue, Apr 22, 2014 at 04:42:20PM +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@xxxxxxxxxx>
> 
> To implement hotplug detection in a race-free manner, drivers must call
> drm_kms_helper_poll_init() before hotplug events can be triggered. Such
> events can be triggered right after any of the encoders or connectors
> are initialized. At the same time, if the drm_fb_helper_hotplug_event()
> helper is used by a driver, then the poll helper requires some parts of
> the FB helper to be initialized to prevent a crash.
> 
> At the same time, drm_fb_helper_init() requires information that is not
> necessarily available at such an early stage (number of CRTCs and
> connectors), so it cannot be used yet.
> 
> Add a new helper, drm_fb_helper_prepare(), that initializes the bare
> minimum needed to allow drm_kms_helper_poll_init() to execute and any
> subsequent hotplug events to be processed properly.
> 
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>

Some bikeshed on the kerneldoc below, with that addressed this is

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

> ---
>  drivers/gpu/drm/armada/armada_fbdev.c     |  2 +-
>  drivers/gpu/drm/ast/ast_fb.c              |  4 ++-
>  drivers/gpu/drm/bochs/bochs_fbdev.c       |  3 ++-
>  drivers/gpu/drm/cirrus/cirrus_fbdev.c     |  4 ++-
>  drivers/gpu/drm/drm_fb_cma_helper.c       |  3 ++-
>  drivers/gpu/drm/drm_fb_helper.c           | 43 ++++++++++++++++++++++++-------
>  drivers/gpu/drm/exynos/exynos_drm_fbdev.c |  3 ++-
>  drivers/gpu/drm/gma500/framebuffer.c      |  3 ++-
>  drivers/gpu/drm/i915/intel_fbdev.c        |  3 ++-
>  drivers/gpu/drm/mgag200/mgag200_fb.c      |  3 ++-
>  drivers/gpu/drm/msm/msm_fbdev.c           |  2 +-
>  drivers/gpu/drm/nouveau/nouveau_fbcon.c   |  3 ++-
>  drivers/gpu/drm/omapdrm/omap_fbdev.c      |  2 +-
>  drivers/gpu/drm/qxl/qxl_fb.c              |  5 +++-
>  drivers/gpu/drm/radeon/radeon_fb.c        |  4 ++-
>  drivers/gpu/drm/tegra/fb.c                |  4 +--
>  drivers/gpu/drm/udl/udl_fb.c              |  3 ++-
>  include/drm/drm_fb_helper.h               |  2 ++
>  18 files changed, 68 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/gpu/drm/armada/armada_fbdev.c b/drivers/gpu/drm/armada/armada_fbdev.c
> index 21aa1261dba2..9437e11d5df1 100644
> --- a/drivers/gpu/drm/armada/armada_fbdev.c
> +++ b/drivers/gpu/drm/armada/armada_fbdev.c
> @@ -149,7 +149,7 @@ int armada_fbdev_init(struct drm_device *dev)
>  
>  	priv->fbdev = fbh;
>  
> -	fbh->funcs = &armada_fb_helper_funcs;
> +	drm_fb_helper_prepare(dev, fbh, &armada_fb_helper_funcs);
>  
>  	ret = drm_fb_helper_init(dev, fbh, 1, 1);
>  	if (ret) {
> diff --git a/drivers/gpu/drm/ast/ast_fb.c b/drivers/gpu/drm/ast/ast_fb.c
> index 2113894e4ff8..cba45c774552 100644
> --- a/drivers/gpu/drm/ast/ast_fb.c
> +++ b/drivers/gpu/drm/ast/ast_fb.c
> @@ -328,8 +328,10 @@ int ast_fbdev_init(struct drm_device *dev)
>  		return -ENOMEM;
>  
>  	ast->fbdev = afbdev;
> -	afbdev->helper.funcs = &ast_fb_helper_funcs;
>  	spin_lock_init(&afbdev->dirty_lock);
> +
> +	drm_fb_helper_prepare(dev, &afbdev->helper, &ast_fb_helper_funcs);
> +
>  	ret = drm_fb_helper_init(dev, &afbdev->helper,
>  				 1, 1);
>  	if (ret) {
> diff --git a/drivers/gpu/drm/bochs/bochs_fbdev.c b/drivers/gpu/drm/bochs/bochs_fbdev.c
> index 17e5c17f2730..19cf3e9413b6 100644
> --- a/drivers/gpu/drm/bochs/bochs_fbdev.c
> +++ b/drivers/gpu/drm/bochs/bochs_fbdev.c
> @@ -189,7 +189,8 @@ int bochs_fbdev_init(struct bochs_device *bochs)
>  {
>  	int ret;
>  
> -	bochs->fb.helper.funcs = &bochs_fb_helper_funcs;
> +	drm_fb_helper_prepare(bochs->dev, &bochs->fb.helper,
> +			      &bochs_fb_helper_funcs);
>  
>  	ret = drm_fb_helper_init(bochs->dev, &bochs->fb.helper,
>  				 1, 1);
> diff --git a/drivers/gpu/drm/cirrus/cirrus_fbdev.c b/drivers/gpu/drm/cirrus/cirrus_fbdev.c
> index 2bd0291168e4..2a135f253e29 100644
> --- a/drivers/gpu/drm/cirrus/cirrus_fbdev.c
> +++ b/drivers/gpu/drm/cirrus/cirrus_fbdev.c
> @@ -306,9 +306,11 @@ int cirrus_fbdev_init(struct cirrus_device *cdev)
>  		return -ENOMEM;
>  
>  	cdev->mode_info.gfbdev = gfbdev;
> -	gfbdev->helper.funcs = &cirrus_fb_helper_funcs;
>  	spin_lock_init(&gfbdev->dirty_lock);
>  
> +	drm_fb_helper_prepare(cdev->dev, &gfbdev->helper,
> +			      &cirrus_fb_helper_funcs);
> +
>  	ret = drm_fb_helper_init(cdev->dev, &gfbdev->helper,
>  				 cdev->num_crtc, CIRRUSFB_CONN_LIMIT);
>  	if (ret) {
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> index b74f9e58b69d..acbbd230e081 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -354,9 +354,10 @@ struct drm_fbdev_cma *drm_fbdev_cma_init(struct drm_device *dev,
>  		return ERR_PTR(-ENOMEM);
>  	}
>  
> -	fbdev_cma->fb_helper.funcs = &drm_fb_cma_helper_funcs;
>  	helper = &fbdev_cma->fb_helper;
>  
> +	drm_fb_helper_prepare(dev, helper, &drm_fb_cma_helper_funcs);
> +
>  	ret = drm_fb_helper_init(dev, helper, num_crtc, max_conn_count);
>  	if (ret < 0) {
>  		dev_err(dev->dev, "Failed to initialize drm fb helper.\n");
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 80ce92ab91f9..7788f110fcbf 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -49,10 +49,11 @@ static LIST_HEAD(kernel_fb_helper_list);
>   * helper functions used by many drivers to implement the kernel mode setting
>   * interfaces.
>   *
> - * Initialization is done as a three-step process with drm_fb_helper_init(),
> - * drm_fb_helper_single_add_all_connectors() and drm_fb_helper_initial_config().
> - * Drivers with fancier requirements than the default behaviour can override the
> - * second step with their own code.  Teardown is done with drm_fb_helper_fini().
> + * Initialization is done as a four-step process with drm_fb_helper_prepare(),
> + * drm_fb_helper_init(), drm_fb_helper_single_add_all_connectors() and
> + * drm_fb_helper_initial_config(). Drivers with fancier requirements than the
> + * default behaviour can override the second step with their own code.
> + * Teardown is done with drm_fb_helper_fini().
>   *
>   * At runtime drivers should restore the fbdev console by calling
>   * drm_fb_helper_restore_fbdev_mode() from their ->lastclose callback. They
> @@ -502,6 +503,33 @@ static void drm_fb_helper_crtc_free(struct drm_fb_helper *helper)
>  }
>  
>  /**
> + * drm_fb_helper_prepare - setup a drm_fb_helper structure
> + * @dev: DRM device
> + * @helper: driver-allocated fbdev helper structure to set up
> + * @funcs: pointer to structure of functions associate with this helper
> + *
> + * Sets up the bare minimum to make the framebuffer helper usable. This is
> + * useful to implement race-free initialization of the polling helpers. In
> + * that case a typical sequence would be:
> + *
> + *   - call drm_fb_helper_prepare()
> + *   - set dev->mode_config.funcs

This step is done in drm_fb_helper_prepare already.

> + *   - perform driver-specific setup
> + *   - call drm_kms_helper_poll_init()

Maybe mention that after this you can start to handle hpd events using the
probe helpers?

> + *   - call drm_fb_helper_init()
> + *   - call drm_fb_helper_single_add_all_connectors()
> + *   - call drm_fb_helper_initial_config()

Does this list look sane in the generated DocBook? Afaik kerneldoc
unfortunately lacks any form of markup, at least afaik :(

> + */
> +void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> +			   const struct drm_fb_helper_funcs *funcs)
> +{
> +	INIT_LIST_HEAD(&helper->kernel_fb_list);
> +	helper->funcs = funcs;
> +	helper->dev = dev;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_prepare);
> +
> +/**
>   * drm_fb_helper_init - initialize a drm_fb_helper structure
>   * @dev: drm device
>   * @fb_helper: driver-allocated fbdev helper structure to initialize
> @@ -513,8 +541,7 @@ static void drm_fb_helper_crtc_free(struct drm_fb_helper *helper)
>   * nor register the fbdev. This is only done in drm_fb_helper_initial_config()
>   * to allow driver writes more control over the exact init sequence.
>   *
> - * Drivers must set fb_helper->funcs before calling
> - * drm_fb_helper_initial_config().
> + * Drivers must call drm_fb_helper_prepare() before calling this function.
>   *
>   * RETURNS:
>   * Zero if everything went ok, nonzero otherwise.
> @@ -529,10 +556,6 @@ int drm_fb_helper_init(struct drm_device *dev,
>  	if (!max_conn_count)
>  		return -EINVAL;
>  
> -	fb_helper->dev = dev;
> -
> -	INIT_LIST_HEAD(&fb_helper->kernel_fb_list);
> -
>  	fb_helper->crtc_info = kcalloc(crtc_count, sizeof(struct drm_fb_helper_crtc), GFP_KERNEL);
>  	if (!fb_helper->crtc_info)
>  		return -ENOMEM;
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
> index 7ccf04917f47..46443971d517 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_fbdev.c
> @@ -274,7 +274,8 @@ int exynos_drm_fbdev_init(struct drm_device *dev)
>  		return -ENOMEM;
>  
>  	private->fb_helper = helper = &fbdev->drm_fb_helper;
> -	helper->funcs = &exynos_drm_fb_helper_funcs;
> +
> +	drm_fb_helper_prepare(dev, helper, &exynos_drm_fb_helper_funcs);
>  
>  	num_crtc = dev->mode_config.num_crtc;
>  
> diff --git a/drivers/gpu/drm/gma500/framebuffer.c b/drivers/gpu/drm/gma500/framebuffer.c
> index 76e4d777d01d..d0dd3bea8aa5 100644
> --- a/drivers/gpu/drm/gma500/framebuffer.c
> +++ b/drivers/gpu/drm/gma500/framebuffer.c
> @@ -600,7 +600,8 @@ int psb_fbdev_init(struct drm_device *dev)
>  	}
>  
>  	dev_priv->fbdev = fbdev;
> -	fbdev->psb_fb_helper.funcs = &psb_fb_helper_funcs;
> +
> +	drm_fb_helper_prepare(dev, &fbdev->psb_fb_helper, &psb_fb_helper_funcs);
>  
>  	drm_fb_helper_init(dev, &fbdev->psb_fb_helper, dev_priv->ops->crtcs,
>  							INTELFB_CONN_LIMIT);
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 336a89f2549e..e7dd21029060 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -600,7 +600,8 @@ int intel_fbdev_init(struct drm_device *dev)
>  	if (ifbdev == NULL)
>  		return -ENOMEM;
>  
> -	ifbdev->helper.funcs = &intel_fb_helper_funcs;
> +	drm_fb_helper_probe(dev, &ifbdev->helper, &intel_fb_helper_funcs);
> +
>  	if (!intel_fbdev_init_bios(dev, ifbdev))
>  		ifbdev->preferred_bpp = 32;
>  
> diff --git a/drivers/gpu/drm/mgag200/mgag200_fb.c b/drivers/gpu/drm/mgag200/mgag200_fb.c
> index a4319aba9180..5451dc58eff1 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_fb.c
> +++ b/drivers/gpu/drm/mgag200/mgag200_fb.c
> @@ -293,9 +293,10 @@ int mgag200_fbdev_init(struct mga_device *mdev)
>  		return -ENOMEM;
>  
>  	mdev->mfbdev = mfbdev;
> -	mfbdev->helper.funcs = &mga_fb_helper_funcs;
>  	spin_lock_init(&mfbdev->dirty_lock);
>  
> +	drm_fb_helper_prepare(mdev->dev, &mfbdev->helper, &mga_fb_helper_funcs);
> +
>  	ret = drm_fb_helper_init(mdev->dev, &mfbdev->helper,
>  				 mdev->num_crtc, MGAG200FB_CONN_LIMIT);
>  	if (ret)
> diff --git a/drivers/gpu/drm/msm/msm_fbdev.c b/drivers/gpu/drm/msm/msm_fbdev.c
> index 841665862f2f..745b1be4acf0 100644
> --- a/drivers/gpu/drm/msm/msm_fbdev.c
> +++ b/drivers/gpu/drm/msm/msm_fbdev.c
> @@ -200,7 +200,7 @@ struct drm_fb_helper *msm_fbdev_init(struct drm_device *dev)
>  
>  	helper = &fbdev->base;
>  
> -	helper->funcs = &msm_fb_helper_funcs;
> +	drm_fb_helper_prepare(dev, helper, &msm_fb_helper_funcs);
>  
>  	ret = drm_fb_helper_init(dev, helper,
>  			priv->num_crtcs, priv->num_connectors);
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.c b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> index 8e9c07b7fc89..afe706a20f97 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> @@ -464,7 +464,8 @@ nouveau_fbcon_init(struct drm_device *dev)
>  
>  	fbcon->dev = dev;
>  	drm->fbcon = fbcon;
> -	fbcon->helper.funcs = &nouveau_fbcon_helper_funcs;
> +
> +	drm_fb_helper_prepare(dev, &fbcon->helper, &nouveau_fbcon_helper_funcs);
>  
>  	ret = drm_fb_helper_init(dev, &fbcon->helper,
>  				 dev->mode_config.num_crtc, 4);
> diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
> index 4cb12083eb12..8436c6857cda 100644
> --- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
> +++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c
> @@ -325,7 +325,7 @@ struct drm_fb_helper *omap_fbdev_init(struct drm_device *dev)
>  
>  	helper = &fbdev->base;
>  
> -	helper->funcs = &omap_fb_helper_funcs;
> +	drm_fb_helper_prepare(dev, helper, &omap_fb_helper_funcs);
>  
>  	ret = drm_fb_helper_init(dev, helper,
>  			priv->num_crtcs, priv->num_connectors);
> diff --git a/drivers/gpu/drm/qxl/qxl_fb.c b/drivers/gpu/drm/qxl/qxl_fb.c
> index cf89614c72be..df567888bb1e 100644
> --- a/drivers/gpu/drm/qxl/qxl_fb.c
> +++ b/drivers/gpu/drm/qxl/qxl_fb.c
> @@ -676,9 +676,12 @@ int qxl_fbdev_init(struct qxl_device *qdev)
>  
>  	qfbdev->qdev = qdev;
>  	qdev->mode_info.qfbdev = qfbdev;
> -	qfbdev->helper.funcs = &qxl_fb_helper_funcs;
>  	spin_lock_init(&qfbdev->delayed_ops_lock);
>  	INIT_LIST_HEAD(&qfbdev->delayed_ops);
> +
> +	drm_fb_helper_prepare(qdev->ddev, &qfbdev->helper,
> +			      &qxl_fb_helper_funcs);
> +
>  	ret = drm_fb_helper_init(qdev->ddev, &qfbdev->helper,
>  				 qxl_num_crtc /* num_crtc - QXL supports just 1 */,
>  				 QXLFB_CONN_LIMIT);
> diff --git a/drivers/gpu/drm/radeon/radeon_fb.c b/drivers/gpu/drm/radeon/radeon_fb.c
> index ad97afdbc4c7..db598d712901 100644
> --- a/drivers/gpu/drm/radeon/radeon_fb.c
> +++ b/drivers/gpu/drm/radeon/radeon_fb.c
> @@ -353,7 +353,9 @@ int radeon_fbdev_init(struct radeon_device *rdev)
>  
>  	rfbdev->rdev = rdev;
>  	rdev->mode_info.rfbdev = rfbdev;
> -	rfbdev->helper.funcs = &radeon_fb_helper_funcs;
> +
> +	drm_fb_helper_prepare(rdev->ddev, &rfbdev->helper,
> +			      &radeon_fb_helper_funcs);
>  
>  	ret = drm_fb_helper_init(rdev->ddev, &rfbdev->helper,
>  				 rdev->num_crtc,
> diff --git a/drivers/gpu/drm/tegra/fb.c b/drivers/gpu/drm/tegra/fb.c
> index 75bed72a9755..2e3758542c89 100644
> --- a/drivers/gpu/drm/tegra/fb.c
> +++ b/drivers/gpu/drm/tegra/fb.c
> @@ -276,7 +276,6 @@ static struct tegra_fbdev *tegra_fbdev_create(struct drm_device *drm,
>  					      unsigned int num_crtc,
>  					      unsigned int max_connectors)
>  {
> -	struct drm_fb_helper *helper;
>  	struct tegra_fbdev *fbdev;
>  	int err;
>  
> @@ -286,8 +285,7 @@ static struct tegra_fbdev *tegra_fbdev_create(struct drm_device *drm,
>  		return ERR_PTR(-ENOMEM);
>  	}
>  
> -	fbdev->base.funcs = &tegra_fb_helper_funcs;
> -	helper = &fbdev->base;
> +	drm_fb_helper_prepare(drm, &fbdev->base, &tegra_fb_helper_funcs);
>  
>  	err = drm_fb_helper_init(drm, &fbdev->base, num_crtc, max_connectors);
>  	if (err < 0) {
> diff --git a/drivers/gpu/drm/udl/udl_fb.c b/drivers/gpu/drm/udl/udl_fb.c
> index 0647c8cc368b..d1da339843ca 100644
> --- a/drivers/gpu/drm/udl/udl_fb.c
> +++ b/drivers/gpu/drm/udl/udl_fb.c
> @@ -583,7 +583,8 @@ int udl_fbdev_init(struct drm_device *dev)
>  		return -ENOMEM;
>  
>  	udl->fbdev = ufbdev;
> -	ufbdev->helper.funcs = &udl_fb_helper_funcs;
> +
> +	drm_fb_helper_prepare(dev, &ufbdev->helper, &udl_fb_helper_funcs);
>  
>  	ret = drm_fb_helper_init(dev, &ufbdev->helper,
>  				 1, 1);
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index e8c8eeb3a253..9b83c66a5f13 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -97,6 +97,8 @@ struct drm_fb_helper {
>  	bool delayed_hotplug;
>  };
>  
> +void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
> +			   const struct drm_fb_helper_funcs *funcs);
>  int drm_fb_helper_init(struct drm_device *dev,
>  		       struct drm_fb_helper *helper, int crtc_count,
>  		       int max_conn);
> -- 
> 1.9.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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