Re: Accessing rpmsg_device in sysfs attribute functions

[Greg KH <greg@kroah.com>]

On Tue, Mar 24, 2020 at 05:34:44AM +0000, Pelle Windestam wrote:
> Hi,
> 
> I am trying to develop a simple driver for the rpmsg bus, in order to send various commands from user space in Linux to a secondary CPU (A Cortex M4). I'm trying to keep things as simple as possible, so my idea was to create a driver that just has a few attributes which can be set in /sys which would trigger commands to be sent to the M4 CPU. I have the communication between the CPU:s up and running, but where I'm having trouble moving forward is how to access the "struct rpmsg_device *" that I need in order to communicate with the endpoint for the M4 CPU from the store/show function of the sysfs attributes. What my driver does is to register a rpmsg_driver in the init function:
> 
> register_rpmsg_driver(&pwm_rpmsg_driver);
> 
> the device_driver member of my rpmsg_driver struct has its groups member set to my driver attribute groups array:
> static struct rpmsg_driver pwm_rpmsg_driver = {
> 	.probe = pwm_rpmsg_probe,
> 	.remove = pwm_rpmsg_remove,
> 	.callback = pwm_rpmsg_cb,
> 	.id_table = pwm_rpmsg_device_id_table,
> 	.drv = {
> 		.groups = driver_pwm_groups,
> 		.name = "pwm_rpmsg",
> 	},
> };
> 
> My issue is that that I am not sure how to access the struct "rpmsg_device *" (i.e. from the probe() function) in the show/store functions for the sysfs attributes, which have a "struct device_driver *" argument:

That is because you have created a driver attribute, not a device
attribute.  Create device attributes and you should be fine, they bind
to the device your driver is passed.

good luck!

greg k-h

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