linux-kernel - Re: [PATCH v2 5/7] rpmsg: char: Introduce a rpmsg driver for the rpmsg char device

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Message-ID: <47015357-b006-1c32-f63f-d4fcac054d6f@foss.st.com>
Date:   Thu, 22 Apr 2021 09:58:27 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
CC:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        <linux-remoteproc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH v2 5/7] rpmsg: char: Introduce a rpmsg driver for the
 rpmsg char device

On 4/21/21 7:40 PM, Mathieu Poirier wrote:
> Good day Arnaud,
> 
> On Tue, Apr 13, 2021 at 03:44:56PM +0200, Arnaud Pouliquen wrote:
>> A rpmsg char device allows to probe the endpoint device on a remote name
>> service announcement.
>>
>> With this patch the /dev/rpmsgX interface is created either by a user
>> application or by the remote firmware.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
>>
>> ---
>> update from V1:
>>  - add missing unregister_rpmsg_driver call on module exit.
>>
>> ---
>>  drivers/rpmsg/rpmsg_char.c | 59 +++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 58 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
>> index a64249d83172..4606787b7011 100644
>> --- a/drivers/rpmsg/rpmsg_char.c
>> +++ b/drivers/rpmsg/rpmsg_char.c
>> @@ -26,6 +26,8 @@
>>  #include "rpmsg_char.h"
>>  #include "rpmsg_internal.h"
>>  
>> +#define RPMSG_CHAR_DEVNAME "rpmsg-raw"
>> +
> 
> Why not simply call it rpmsg-char?

I would avoid to link the rpmsg name service to the Linux Kernel device.

> 
>>  static dev_t rpmsg_major;
>>  
>>  static DEFINE_IDA(rpmsg_ept_ida);
>> @@ -403,13 +405,67 @@ int rpmsg_chrdev_create_eptdev(struct rpmsg_device *rpdev, struct device *parent
>>  }
>>  EXPORT_SYMBOL(rpmsg_chrdev_create_eptdev);
>>  
>> +static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
>> +{
>> +	struct rpmsg_channel_info chinfo;
>> +	struct rpmsg_eptdev *eptdev;
>> +
>> +	if (!rpdev->ept)
>> +		return -EINVAL;
>> +
>> +	memcpy(chinfo.name, RPMSG_CHAR_DEVNAME, sizeof(RPMSG_CHAR_DEVNAME));
>> +	chinfo.src = rpdev->src;
>> +	chinfo.dst = rpdev->dst;
>> +
>> +	eptdev = __rpmsg_chrdev_create_eptdev(rpdev, &rpdev->dev, chinfo, NULL);
>> +	if (IS_ERR(eptdev))
>> +		return PTR_ERR(eptdev);
>> +
>> +	/* Set the private field of the default endpoint to retrieve context on callback. */
>> +	rpdev->ept->priv = eptdev;
> 
> This is already done in rpmsg_create_ept() when rpmsg_eptdev_open() is called.
> 
>> +
>> +	return 0;
>> +}
>> +
>> +static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
>> +{
>> +	int ret;
>> +
>> +	ret = device_for_each_child(&rpdev->dev, NULL, rpmsg_chrdev_destroy_eptdev);
>> +	if (ret)
>> +		dev_warn(&rpdev->dev, "failed to destroy endpoints: %d\n", ret);
>> +}
>> +
>> +static struct rpmsg_device_id rpmsg_chrdev_id_table[] = {
>> +	{ .name	= RPMSG_CHAR_DEVNAME },
>> +	{ },
>> +};
>> +
>> +static struct rpmsg_driver rpmsg_chrdev_driver = {
>> +	.probe = rpmsg_chrdev_probe,
>> +	.remove = rpmsg_chrdev_remove,
>> +	.id_table = rpmsg_chrdev_id_table,
>> +	.callback = rpmsg_ept_cb,
> 
> Not sure why we need a callback associated to this driver when
> rpmsg_eptdev_open() already creates and rpmsg_endpoint.  To me the only thing
> having a callback provides is the association between the rpmsg_device and the
> rpmsg_endpoint[1] that happens in rpmsg_dev_probe().  The QC folks already do
> this association in their platform code[2].  Since this is not done in
> __rpmsg_create_ept() a check for rpdev->ept == NULL could be done in
> rpmsg_eptdev_open() and do the assignment there. 
> 
> [1]. https://elixir.bootlin.com/linux/v5.12-rc6/source/drivers/rpmsg/rpmsg_core.c#L513  
> [2]. https://elixir.bootlin.com/linux/v5.12-rc6/source/drivers/rpmsg/qcom_glink_native.c#L1623
> 

That's a good point! When I started the redesign, I faced some issues with the
approach you propose. But as I can not remember the reason and because the code
has evolved, i need to re-think about this.

Thanks,
Arnaud


>> +	.drv = {
>> +		.name = "rpmsg_chrdev",
>> +	},
>> +};
>> +
>>  static int rpmsg_chrdev_init(void)
>>  {
>>  	int ret;
>>  
>>  	ret = alloc_chrdev_region(&rpmsg_major, 0, RPMSG_DEV_MAX, "rpmsg_char");
>> -	if (ret < 0)
>> +	if (ret < 0) {
>>  		pr_err("rpmsg: failed to allocate char dev region\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = register_rpmsg_driver(&rpmsg_chrdev_driver);
>> +	if (ret < 0) {
>> +		pr_err("rpmsg: failed to register rpmsg raw driver\n");
>> +		unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
>> +	}
>>  
>>  	return ret;
>>  }
>> @@ -417,6 +473,7 @@ postcore_initcall(rpmsg_chrdev_init);
>>  
>>  static void rpmsg_chrdev_exit(void)
>>  {
>> +	unregister_rpmsg_driver(&rpmsg_chrdev_driver);
>>  	unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
>>  }
>>  module_exit(rpmsg_chrdev_exit);
>> -- 
>> 2.17.1
>>