linux-kernel - Re: [PATCH v2 04/16] rpmsg: ctrl: implement the ioctl function to create device

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Date:   Thu, 28 Jan 2021 17:13:03 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Andy Gross <agross@...nel.org>,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 04/16] rpmsg: ctrl: implement the ioctl function to
 create device

[...]

> > It seems to me that the main point to step forward is to clarify the global
> > design and features of the rpmsg-ctrl.
> > Depending on the decision taken, this series could be trashed and rewritten from
> > a blank page...To not lost to much time on the series don't hesitate to limit
> > the review to the minimum.
> > 
> 
> I doubt you will ever get clear guidelines on the whole solution.  I will get
> back to you once I am done with the SMD driver, which should be in the
> latter part of next week.
>

After looking at the rpmsg_chrdev driver, its current customers (i.e the Qcom
drivers), the rpmsg name service and considering the long term goals of this
patchset I have the following guidelines: 

1) I thought long and hard about how to split the current rpmsg_chrdev driver
between the control plane and the raw device plane and the end solution looks
much slimpler than I expected.  Exporting function rpmsg_eptdev_create() after
moving it to another file (along with other dependencies) should be all we need.
Calling rpmsg_eptdev_create() from rpmsg_ctrldev_ioctl() will automatically load
the new driver, the same way calling rpmsg_ns_register_device() from
rpmsg_probe() took care of loading the rpmsg_ns driver.

2) While keeping the control plane functionality related to
RPMSG_CREATE_EPT_IOCTL intact, introduce a new RPMSG_CREATE_DEV_IOCTL that will
allow for the instantiation of rpmsg_devices, exactly the same way a name service
announcement from a remote processor does.  I envision that code path to
eventually call rpmsg_create_channel().

3) Leave the rpmsg_channel_info structure intact and use the
rpmsg_channel_info::name to bind to a rpmsg_driver, exactly how it is currently
done for name service driver selection.  That will allow us to re-use the
current rpmsg_bus intrastructure, i.e rpmsg_bus::match(), without having to deal
with yet another bus type.  Proceeding this way gives us the opportunity to keep
the current channel name convention for other rpmch_chrdev users untouched.

4) In a prior conversation you indicated the intention of instantiating the
rpmsg_chrdev from the name service interface.  I agree with doing so but 
conjugating that with the RPMSG_CHAR kenrel define may be tricky.  I will wait
to see what you come up with.

I hope this helps.

Thanks,
Mathieu

> > Thanks,
> > Arnaud
> > 
> > > 
> > > Thanks,
> > > Mathieu
> > > 
> > >> +	return NULL;
> > >> +}
> > >> +
> > >>  static long rpmsg_ctrl_dev_ioctl(struct file *fp, unsigned int cmd,
> > >>  				 unsigned long arg)
> > >>  {
> > >>  	struct rpmsg_ctrl_dev *ctrldev = fp->private_data;
> > >> -
> > >> -	dev_info(&ctrldev->dev, "Control not yet implemented\n");
> > >> +	void __user *argp = (void __user *)arg;
> > >> +	struct rpmsg_channel_info chinfo;
> > >> +	struct rpmsg_endpoint_info eptinfo;
> > >> +	struct rpmsg_device *newch;
> > >> +
> > >> +	if (cmd != RPMSG_CREATE_EPT_IOCTL)
> > >> +		return -EINVAL;
> > >> +
> > >> +	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
> > >> +		return -EFAULT;
> > >> +
> > >> +	/*
> > >> +	 * In a frst step only the rpmsg_raw service is supported.
> > >> +	 * The override is foorced to RPMSG_RAW_SERVICE
> > >> +	 */
> > >> +	chinfo.driver_override = rpmsg_ctrl_get_drv_name(RPMSG_RAW_SERVICE);
> > >> +	if (!chinfo.driver_override)
> > >> +		return -ENODEV;
> > >> +
> > >> +	memcpy(chinfo.name, eptinfo.name, RPMSG_NAME_SIZE);
> > >> +	chinfo.name[RPMSG_NAME_SIZE - 1] = '\0';
> > >> +	chinfo.src = eptinfo.src;
> > >> +	chinfo.dst = eptinfo.dst;
> > >> +
> > >> +	newch = rpmsg_create_channel(ctrldev->rpdev, &chinfo);
> > >> +	if (!newch) {
> > >> +		dev_err(&ctrldev->dev, "rpmsg_create_channel failed\n");
> > >> +		return -ENXIO;
> > >> +	}
> > >>  
> > >>  	return 0;
> > >>  };
> > >> -- 
> > >> 2.17.1
> > >>