Den 10.02.2019 22.03, skrev Sam Ravnborg:
> 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@xxxxxxxxxxx>
>
> 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.
Using devm_drm_dev_init() doesn't affect the use of shutdown(), and for
remove() it only saves one drm_dev_put(). The main benefit that I see is
for a simpler probe() function.
Maybe the last part can be:
The example is used to demonstrate the use of devm_drm_dev_init() and
its accompanying drm_driver->release callback.
Thanks for helping me with this. Daniel is big on documentation so I try
to follow up, but words for humans isn't my strong side :-)
>
>
>> + *
>> + * .. code-block:: c
>> + *
>> + * struct driver_device {
>> + * struct drm_device drm;
Maybe I should add a comment for userspace_facing:
* [ Represents a resource that is accessed by userspace ]
>> + * 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...
That makes sense:
devm_kzalloc() can't be used here because the drm_device lifetime can
exceed the device lifetime if driver unbind happens when userspace still
has open file descriptors.
>
>> + * 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?
>
This is where one benfit of device managed resources kicks in.
If probing fails, happens in drivers/base/dd.c:really_probe(),
devres_release_all() is called which results in:
devm_drm_dev_init_release() -> drm_dev_put() -> driver_drm_release().
If the driver only uses devm_ managed resources or releases the
resource(s) in drm_driver->release, there's no need for an error path in
the probe function.
The ->userspace_facing resource is an attempt to showcase a resource
that is released in drm_driver->release, but I'm unsure if it's really a
good example. It would have been better to have a real world example.
>> + *
>> + * 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);
You asked about drm_dev_unplug() in the other patch. It is used if the
driver supports device unplug, like for USB or unloading a Device Tree
overlay (not sure if all the pieces exists in mainline yet for that).
Maybe I can add this section after the example:
Drivers that want to support device unplugging (USB, DT overlay unload)
should use drm_dev_unplug() instead of drm_dev_unregister(). The driver
must protect regions that is accessing device resources to avoid use
after they're released. This is done using drm_dev_enter() and
drm_dev_exit(). There is one shortcoming however, drm_dev_unplug() marks
the drm_device as unplugged before drm_atomic_helper_shutdown() is
called. This means that if the disable code paths are protected, they
will not run on regular driver module unload, possibily leaving the
hardware enabled.
>> + * drm_atomic_helper_shutdown(drm)
>> + *
>> + * return 0;
>> + * }
>> + *
I can add a comment for shutdown:
This function is called on kernel restart and shutdown
>> + * 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
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@xxxxxxxxxxxxxxxxxxxxx
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
