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From: Pelle Windestam <Pelle.Windestam@tagmaster.com>
To: Greg KH <greg@kroah.com>
Cc: "kernelnewbies@kernelnewbies.org" <kernelnewbies@kernelnewbies.org>
Subject: RE: Accessing rpmsg_device in sysfs attribute functions
Date: Tue, 24 Mar 2020 12:02:15 +0000
Message-ID: <a8357c5f3c4c4f29a7c5105b0306cd47@tagmaster.com> (raw)
In-Reply-To: <20200324063113.GA1978604@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.

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.

//Pelle
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Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24  5:34 Pelle Windestam
2020-03-24  6:31 ` Greg KH
2020-03-24  9:49   ` Martin Kaiser
2020-03-24 10:23     ` Greg KH
2020-03-24 12:02   ` Pelle Windestam [this message]
2020-03-24 12:31     ` Greg KH
2020-03-24 13:05       ` Pelle Windestam
2020-03-24 13:15         ` Greg KH
2020-03-24 13:35           ` Pelle Windestam

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