Re: [PATCH v2 03/12] drm/drv: DOC: Add driver example code

[Sam Ravnborg <sam@ravnborg.org>]

Hi Noralf

On Sun, Feb 10, 2019 at 02:10:30PM +0100, Noralf Trønnes wrote:
> Add driver example that shows how devm_drm_dev_init() can be used.
> 
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>

Always good with examples!


> ---
> 
> I'm not sure how detailed such an example such be and a description of 
> some kind is also required. Help is needed :-)
> 
> Noralf.
> 
>  drivers/gpu/drm/drm_drv.c | 118 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 118 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 351f128ec4b7..99ca3551688f 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -286,6 +286,124 @@ void drm_minor_release(struct drm_minor *minor)
>   * Note that the lifetime rules for &drm_device instance has still a lot of
>   * historical baggage. Hence use the reference counting provided by
>   * drm_dev_get() and drm_dev_put() only carefully.
> + *
> + * Display driver example
> + * ~~~~~~~~~~~~~~~~~~~~~~

Maybe add something like this:

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.
The example is used to demonstrate the use of devm_drm_dev_init(), and
shows how the use of a device managed drm_device allows for simpler
remove() and shuttdown() functions.


> + *
> + * .. code-block:: c
> + *
> + *	struct driver_device {
> + *		struct drm_device drm;
> + *		void *userspace_facing;
> + *		struct clk *pclk;
> + *	};
> + *
> + *	static inline struct driver_device *drm_to_priv(struct drm_device *drm)
> + *	{
> + *		return container_of(drm, struct driver_device, drm);
> + *	}
> + *
> + *	static void driver_drm_release(struct drm_device *drm)
> + *	{
> + *		struct driver_device *priv = drm_to_priv(drm);
> + *
> + *		drm_mode_config_cleanup(drm);
> + *		drm_dev_fini(drm);
> + *		kfree(priv->userspace_facing);
> + *		kfree(priv);
> + *	}
> + *
> + *	static struct drm_driver driver_drm_driver = {
> + *		[...]
> + *		.release = driver_drm_release,
> + *	};
> + *
> + *	static int driver_probe(struct platform_device *pdev)
> + *	{
> + *		struct driver_device *priv;
> + *		struct drm_device *drm;
> + *		int ret;
> + *
> + *		priv = kzalloc(sizeof(*priv), GFP_KERNEL);
Add a comment that explains why we cannot use devm_kzalloc()?
It is used in a lot of places today...

> + *		if (!priv)
> + *			return -ENOMEM;
> + *
> + *		drm = &priv->drm;
> + *
> + *		ret = devm_drm_dev_init(&pdev->dev, drm, &driver_drm_driver);
> + *		if (ret) {
> + *			kfree(drm);
This should be kfree(priv);

> + *			return ret;
> + *		}
> + *
> + *		drm_mode_config_init(drm);
> + *
> + *		priv->userspace_facing = kzalloc(..., GFP_KERNEL);
> + *		if (!priv->userspace_facing)
> + *			return -ENOMEM;
If we fail here we should also free priv?

> + *
> + *		priv->pclk = devm_clk_get(dev, "PCLK");
> + *		if (IS_ERR(priv->pclk))
> + *			return PTR_ERR(priv->pclk);
> + *
> + *		[ Further setup, display pipeline etc ]
> + *
> + *		drm_mode_config_reset(drm);
> + *
> + *		ret = drm_dev_register(drm);
> + *		if (ret)
> + *			return ret;
> + *
> + *		platform_set_drvdata(pdev, drm);
> + *
> + *		drm_fbdev_generic_setup(drm, 32);
> + *
> + *		return 0;
> + *	}
> + *
> + *	[ This function is called before the devm_ resources are released ]
> + *	static int driver_remove(struct platform_device *pdev)
> + *	{
> + *		struct drm_device *drm = platform_get_drvdata(pdev);
> + *
> + *		drm_dev_unregister(drm);
> + *		drm_atomic_helper_shutdown(drm)
> + *
> + *		return 0;
> + *	}
> + *
> + *	static void driver_shutdown(struct platform_device *pdev)
> + *	{
> + *		drm_atomic_helper_shutdown(platform_get_drvdata(pdev));
> + *	}
> + *
> + *	static int __maybe_unused driver_pm_suspend(struct device *dev)
> + *	{
> + *		return drm_mode_config_helper_suspend(dev_get_drvdata(dev));
> + *	}
> + *
> + *	static int __maybe_unused driver_pm_resume(struct device *dev)
> + *	{
> + *		drm_mode_config_helper_resume(dev_get_drvdata(dev));
> + *
> + *		return 0;
> + *	}
> + *
> + *	static const struct dev_pm_ops driver_pm_ops = {
> + *		SET_SYSTEM_SLEEP_PM_OPS(driver_pm_suspend, driver_pm_resume)
> + *	};
> + *
> + *	static struct platform_driver driver_driver = {
> + *		.driver = {
> + *			[...]
> + *			.pm = &driver_pm_ops,
> + *		},
> + *		.probe = driver_probe,
> + *		.remove = driver_remove,
> + *		.shutdown = driver_shutdown,
> + *	};
> + *	module_platform_driver(driver_driver);
> + *
>   */
>  
>  /**
> -- 
> 2.20.1
> 
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