Re: Accessing rpmsg_device in sysfs attribute functions

[Greg KH <greg@kroah.com>]

On Tue, Mar 24, 2020 at 12:02:15PM +0000, Pelle Windestam wrote:
> > 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.
> 
> Thanks! Changing them to device attributes was a breeze. Now I am
> slightly confused about the "struct device *" argument to the
> store/show functions. I was under the impression that this would be
> the "struct device" in the struct rpmsg_device, (which would let me
> get the struct rpmsg_device using container_of()?), but it appears to
> be some completely other device (by looking at the pointer address). I
> have tried searching the kernel code for similar example, but I have
> not found anything so far. It feels like I am stumbling a bit in the
> dark here, looking for my rpmsg_device.

It's a bit hard to figure out what exactly you are doing here without a
pointer to the code itself :)

Are you sure you aren't pointing the platform device accidentally?

thanks,

greg k-h

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