Re: [Intel-gfx] [PATCH 26/51] drm: Manage drm_mode_config_init with drmm_

[Sam Ravnborg <sam@ravnborg.org>]

Hi Daniel.

On Mon, Mar 02, 2020 at 11:26:06PM +0100, Daniel Vetter wrote:
> drm_mode_config_cleanup is idempotent, so no harm in calling this
> twice. This allows us to gradually switch drivers over by removing
> explicit drm_mode_config_cleanup calls.
> 
> With this step it's now also possible that (at least for simple
> drivers) automatic resource cleanup can be done correctly without a
> drm_driver->release hook. Therefore allow this now in
> devm_drm_dev_init().
> 
> Also with drmm_ explicit drm_driver->release hooks are kinda not the
> best option: Drivers can always just register their current release
> hook with drmm_add_action, but even better they could split them up to
> simplify the unwinding for the driver load failure case. So deprecate
> that hook to discourage future users.
> 
> v2: Fixup the example in the kerneldoc too.
> 
> v3:
> - For paranoia, double check that minor->dev == dev in the release
>   hook, because I botched the pointer math in the drmm library.
> - Call drm_mode_config_cleanup when drmm_add_action fails, we'd be
>   missing some mutex_destroy and ida_cleanup otherwise (Laurent)
> 
> v4: Add a drmm_add_action_or_reset (like devm_ has) to encapsulate this
> pattern (Noralf).
> 
> v5: Fix oversight in the new drmm_add_action_or_reset macro (Noralf)
> 
> v4: Review from Sam:
> - drmm_mode_config_init wrapper (also suggested by Thomas)
> - improve commit message, explain better why ->relase is deprecated

The idea was to rename drm_mode_config_init() to
drmm_mode_config_init().
And then provide a wrapper for backward compatibility.
- So the kernel-doc documented function in drm_mode_config.c is the
  recommened choice
- And the wrapper in drm_mode_config.h was only for backward
  compatibility

In other words - the wrapper should be an undocumented:
static inline int drm_mode_config_init(struct drm_device *dev)
{
	return drmm_mode_config_init(dev);
}

When all users have transitioned to drmm_mode_config_init()
then the wrapper could be dropped.

With this fixed, or a good reason not to do so:

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

	Sam

> 
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: "Noralf Trønnes" <noralf@tronnes.org>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Acked-by: Noralf Trønnes <noralf@tronnes.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_drv.c         | 23 +++++++----------------
>  drivers/gpu/drm/drm_managed.c     | 14 ++++++++++++++
>  drivers/gpu/drm/drm_mode_config.c | 13 ++++++++++++-
>  include/drm/drm_managed.h         |  7 +++++++
>  include/drm/drm_mode_config.h     | 19 ++++++++++++++++++-
>  5 files changed, 58 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index c709a0ce018c..a82702d0c2fb 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -98,6 +98,8 @@ static void drm_minor_alloc_release(struct drm_device *dev, void *data)
>  	struct drm_minor *minor = data;
>  	unsigned long flags;
>  
> +	WARN_ON(dev != minor->dev);
> +
>  	put_device(minor->kdev);
>  
>  	spin_lock_irqsave(&drm_minor_lock, flags);
> @@ -267,8 +269,7 @@ void drm_minor_release(struct drm_minor *minor)
>   *
>   * The following example shows a typical structure of a DRM display driver.
>   * The example focus on the probe() function and the other functions that is
> - * almost always present and serves as a demonstration of devm_drm_dev_init()
> - * usage with its accompanying drm_driver->release callback.
> + * almost always present and serves as a demonstration of devm_drm_dev_init().
>   *
>   * .. code-block:: c
>   *
> @@ -278,16 +279,8 @@ void drm_minor_release(struct drm_minor *minor)
>   *		struct clk *pclk;
>   *	};
>   *
> - *	static void driver_drm_release(struct drm_device *drm)
> - *	{
> - *		struct driver_device *priv = container_of(...);
> - *
> - *		drm_mode_config_cleanup(drm);
> - *	}
> - *
>   *	static struct drm_driver driver_drm_driver = {
>   *		[...]
> - *		.release = driver_drm_release,
>   *	};
>   *
>   *	static int driver_probe(struct platform_device *pdev)
> @@ -312,7 +305,9 @@ void drm_minor_release(struct drm_minor *minor)
>   *		}
>   *		drmm_add_final_kfree(drm, priv);
>   *
> - *		drm_mode_config_init(drm);
> + *		ret = drm_mode_config_init(drm);
> + *		if (ret)
> + *			return ret;
>   *
>   *		priv->userspace_facing = drmm_kzalloc(..., GFP_KERNEL);
>   *		if (!priv->userspace_facing)
> @@ -710,8 +705,7 @@ static void devm_drm_dev_init_release(void *data)
>   * @driver: DRM driver
>   *
>   * Managed drm_dev_init(). The DRM device initialized with this function is
> - * automatically put on driver detach using drm_dev_put(). You must supply a
> - * &drm_driver.release callback to control the finalization explicitly.
> + * automatically put on driver detach using drm_dev_put().
>   *
>   * RETURNS:
>   * 0 on success, or error code on failure.
> @@ -722,9 +716,6 @@ int devm_drm_dev_init(struct device *parent,
>  {
>  	int ret;
>  
> -	if (WARN_ON(!driver->release))
> -		return -EINVAL;
> -
>  	ret = drm_dev_init(dev, driver, parent);
>  	if (ret)
>  		return ret;
> diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> index 0883615c2088..8c5f1f03c485 100644
> --- a/drivers/gpu/drm/drm_managed.c
> +++ b/drivers/gpu/drm/drm_managed.c
> @@ -142,6 +142,20 @@ int __drmm_add_action(struct drm_device *dev,
>  }
>  EXPORT_SYMBOL(__drmm_add_action);
>  
> +int __drmm_add_action_or_reset(struct drm_device *dev,
> +			       drmres_release_t action,
> +			       void *data, const char *name)
> +{
> +	int ret;
> +
> +	ret = __drmm_add_action(dev, action, data, name);
> +	if (ret)
> +		action(dev, data);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(__drmm_add_action_or_reset);
> +
>  void drmm_remove_action(struct drm_device *dev,
>  			drmres_release_t action,
>  			void *data)
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 08e6eff6a179..6f7005bc597f 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -25,6 +25,7 @@
>  #include <drm/drm_drv.h>
>  #include <drm/drm_encoder.h>
>  #include <drm/drm_file.h>
> +#include <drm/drm_managed.h>
>  #include <drm/drm_mode_config.h>
>  #include <drm/drm_print.h>
>  #include <linux/dma-resv.h>
> @@ -373,6 +374,11 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
>  	return 0;
>  }
>  
> +static void drm_mode_config_init_release(struct drm_device *dev, void *ptr)
> +{
> +	drm_mode_config_cleanup(dev);
> +}
> +
>  /**
>   * drm_mode_config_init - initialize DRM mode_configuration structure
>   * @dev: DRM device
> @@ -384,8 +390,10 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
>   * problem, since this should happen single threaded at init time. It is the
>   * driver's problem to ensure this guarantee.
>   *
> + * Cleanup is automatically handled through registering drm_mode_config_cleanup
> + * with drmm_add_action().
>   */
> -void drm_mode_config_init(struct drm_device *dev)
> +int drm_mode_config_init(struct drm_device *dev)
>  {
>  	mutex_init(&dev->mode_config.mutex);
>  	drm_modeset_lock_init(&dev->mode_config.connection_mutex);
> @@ -443,6 +451,9 @@ void drm_mode_config_init(struct drm_device *dev)
>  		drm_modeset_acquire_fini(&modeset_ctx);
>  		dma_resv_fini(&resv);
>  	}
> +
> +	return drmm_add_action_or_reset(dev, drm_mode_config_init_release,
> +					NULL);
>  }
>  EXPORT_SYMBOL(drm_mode_config_init);
>  
> diff --git a/include/drm/drm_managed.h b/include/drm/drm_managed.h
> index 2b1ba2ad5582..1e6291407586 100644
> --- a/include/drm/drm_managed.h
> +++ b/include/drm/drm_managed.h
> @@ -18,6 +18,13 @@ int __must_check __drmm_add_action(struct drm_device *dev,
>  				   drmres_release_t action,
>  				   void *data, const char *name);
>  
> +#define drmm_add_action_or_reset(dev, action, data) \
> +	__drmm_add_action_or_reset(dev, action, data, #action)
> +
> +int __must_check __drmm_add_action_or_reset(struct drm_device *dev,
> +					    drmres_release_t action,
> +					    void *data, const char *name);
> +
>  void drmm_remove_action(struct drm_device *dev,
>  			drmres_release_t action,
>  			void *data);
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index 3bcbe30339f0..aa6288bf04df 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -929,7 +929,24 @@ struct drm_mode_config {
>  	const struct drm_mode_config_helper_funcs *helper_private;
>  };
>  
> -void drm_mode_config_init(struct drm_device *dev);
> +int drm_mode_config_init(struct drm_device *dev);
> +
> +/**
> + * drmm_mode_config_init - managed DRM mode_configuration structure
> + * 	initialization
> + * @dev: DRM device
> + *
> + * This is a managed version of drm_mode_config_init(). The only difference is
> + * that this version is annotated with __must_check, to make sure that drivers
> + * can actually rely on the automatic cleanup.
> + *
> + * Returns: 0 on success, negative error value on failure.
> + */
> +static inline __must_check int drmm_mode_config_init(struct drm_device *dev)
> +{
> +	return drm_mode_config_init(dev);
> +}
> +
>  void drm_mode_config_reset(struct drm_device *dev);
>  void drm_mode_config_cleanup(struct drm_device *dev);
>  
> -- 
> 2.24.1
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