Date:   Fri, 22 Jan 2021 13:59:34 -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

On Fri, Jan 22, 2021 at 02:05:27PM +0100, Arnaud POULIQUEN wrote:
> Hi Mathieu,
> 
> On 1/22/21 12:52 AM, Mathieu Poirier wrote:
> > On Tue, Dec 22, 2020 at 11:57:14AM +0100, Arnaud Pouliquen wrote:
> >> Implement the ioctl function that parses the list of
> >> rpmsg drivers registered to create an associated device.
> >> To be ISO user API, in a first step, the driver_override
> >> is only allowed for the RPMsg raw service, supported by the
> >> rpmsg_char driver.
> >>
> >> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
> >> ---
> >>  drivers/rpmsg/rpmsg_ctrl.c | 43 ++++++++++++++++++++++++++++++++++++--
> >>  1 file changed, 41 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
> >> index 065e2e304019..8381b5b2b794 100644
> >> --- a/drivers/rpmsg/rpmsg_ctrl.c
> >> +++ b/drivers/rpmsg/rpmsg_ctrl.c
> >> @@ -56,12 +56,51 @@ static int rpmsg_ctrl_dev_open(struct inode *inode, struct file *filp)
> >>  	return 0;
> >>  }
> >>  
> >> +static const char *rpmsg_ctrl_get_drv_name(u32 service)
> >> +{
> >> +	struct rpmsg_ctl_info *drv_info;
> >> +
> >> +	list_for_each_entry(drv_info, &rpmsg_drv_list, node) {
> >> +		if (drv_info->ctrl->service == service)
> >> +			return drv_info->ctrl->drv_name;
> >> +	}
> >> +
> > 
> > I'm unsure about the above... To me this looks like what the .match() function
> > of a bus would do.  And when I read Bjorn's comment he brought up the
> > auxiliary_bus.  I don't know about the auxiliary_bus but it is worth looking
> > into.  Registering with a bus would streamline a lot of the code in this
> > patchset.
> 
> As answered Bjorn, we already have the RPMsg bus to manage the rpmsg devices.
> Look like duplication from my POV, except if the IOCTL does not manage channel
> but only endpoint.
> 
> In my design I considered that the rpmsg_ctrl creates a channel associated to a
> rpmsg_device such as the RPMsg ns_announcement.
> 
> Based on this assumption, if we implement the auxiliary_bus (or other) for the
> rpmsg_ctrl a RPMsg driver will have to manage the probe by rpmsg_bus and by the
> auxillary bus. The probe from the auxiliary bus would lead to the creation of an
> RPMsg device on the rpmsg_bus, so a duplication with cross dependencies and
> would probably make tricky the remove part.
> 
> That said, I think the design depends on the functionality that should be
> implemented in the rpmsg_ctrl. Here is an alternative approach based on the
> auxiliary bus, which I'm starting to think about:
> 
> The current approach of the rpmsg_char driver is to use the IOCTRL interface to
> instantiate a cdev with an endpoint (the RPMsg device is associated with the
> ioctl dev). This would correspond to the use of an auxiliary bus to manage local
> endpoint creations.
> 
> We could therefore consider an RPMsg name service based on an RPmsg device. This
> RPMsg device would register a kind of "RPMsg service endpoint" driver on the
> auxiliary rpmsg_ioctl bus.
> The rpmsg_ctrl will be used to instantiate the endpoints for this RPMsg device.
> on user application request the rpmsg_ctrl will call the appropriate auxiliary
> device to create an endpoint.
> 
> If we consider that one objective of this series is to allow application to
> initiate the communication with the remote processor, so to be able to initiate
> the service (ns announcement sent to the remote processor).
> This implies that:
> -either the RPMsg device has been probed first by a remote ns announcement or by
> a Linux kernel driver using the "driver_override", to register an auxiliary
> device. In this case an endpoint will be created associated to the RPMsg service
> - or create a RPMsg device on first ioctl endpoint creation request, if it does
> not exist (that could trig a NS announcement to remote processor).
> 
> But I'm not sure that this approach would work with QCOM RPMsg backends...
>

I don't think there is a way forward with this set without a clear understanding
of the Glink and SMD drivers.  I have already spent a fair amount of time in the
Glink driver and will continue on Monday with SMD.  

> > 
> > I'm out of time for today - I will continue tomorrow.
> 
> 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.

> 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
> >>

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