Date:   Thu, 3 Sep 2020 17:00:09 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@...com>
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 5/8] rpmsg: introduce reserved rpmsg driver for ns
 announcement

On Tue, Aug 25, 2020 at 06:49:04PM +0200, Arnaud Pouliquen wrote:
> The name service announcement should not be linked to the RPMsg virtio bus
> but to the RPMsg protocol itself.
> 
> This patch proposes to break the dependency with the RPmsg virtio bus by
> the introduction of the reserved RPMsg name service driver which will be in
> charge of managing the RPMsg name service announcement.
> 
> This first patch only implements the probe and the RPMsg endpoint to
> manage create and release channels remote requests.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...com>
> ---
>  drivers/rpmsg/Kconfig          |   8 ++
>  drivers/rpmsg/Makefile         |   1 +
>  drivers/rpmsg/rpmsg_internal.h |  17 +++++
>  drivers/rpmsg/rpmsg_ns.c       | 135 +++++++++++++++++++++++++++++++++
>  4 files changed, 161 insertions(+)
>  create mode 100644 drivers/rpmsg/rpmsg_ns.c
> 
> diff --git a/drivers/rpmsg/Kconfig b/drivers/rpmsg/Kconfig
> index f96716893c2a..c3fc75e6514b 100644
> --- a/drivers/rpmsg/Kconfig
> +++ b/drivers/rpmsg/Kconfig
> @@ -15,6 +15,14 @@ config RPMSG_CHAR
>  	  in /dev. They make it possible for user-space programs to send and
>  	  receive rpmsg packets.
>  
> +config RPMSG_NS
> +	tristate "RPMSG name service announcement"
> +	depends on RPMSG
> +	help
> +	  Say Y here to enable the support of the name service announcement
> +	  channel that probes the associated RPMsg device on remote endpoint
> +	  service announcement.
> +
>  config RPMSG_MTK_SCP
>  	tristate "MediaTek SCP"
>  	depends on MTK_SCP
> diff --git a/drivers/rpmsg/Makefile b/drivers/rpmsg/Makefile
> index ffe932ef6050..8d452656f0ee 100644
> --- a/drivers/rpmsg/Makefile
> +++ b/drivers/rpmsg/Makefile
> @@ -1,6 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_RPMSG)		+= rpmsg_core.o
>  obj-$(CONFIG_RPMSG_CHAR)	+= rpmsg_char.o
> +obj-$(CONFIG_RPMSG_NS)		+= rpmsg_ns.o
>  obj-$(CONFIG_RPMSG_MTK_SCP)	+= mtk_rpmsg.o
>  qcom_glink-objs			:= qcom_glink_native.o qcom_glink_ssr.o
>  obj-$(CONFIG_RPMSG_QCOM_GLINK) += qcom_glink.o
> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
> index d5ab286d0e5e..641b48f6bf2a 100644
> --- a/drivers/rpmsg/rpmsg_internal.h
> +++ b/drivers/rpmsg/rpmsg_internal.h
> @@ -102,4 +102,21 @@ static inline int rpmsg_chrdev_register_device(struct rpmsg_device *rpdev)
>  	return rpmsg_register_device(rpdev);
>  }
>  
> +/**
> + * rpmsg_ns_register_device() - register name service device based on rpdev
> + * @rpdev: prepared rpdev to be used for creating endpoints
> + *
> + * This function wraps rpmsg_register_device() preparing the rpdev for use as
> + * basis for the rpmsg name service device.
> + */
> +static inline int rpmsg_ns_register_device(struct rpmsg_device *rpdev)
> +{
> +	strcpy(rpdev->id.name, "rpmsg_ns");
> +	rpdev->driver_override = "rpmsg_ns";
> +	rpdev->src = RPMSG_NS_ADDR;
> +	rpdev->dst = RPMSG_NS_ADDR;
> +
> +	return rpmsg_register_device(rpdev);
> +}
> +
>  #endif
> diff --git a/drivers/rpmsg/rpmsg_ns.c b/drivers/rpmsg/rpmsg_ns.c
> new file mode 100644
> index 000000000000..3c929b6976a6
> --- /dev/null
> +++ b/drivers/rpmsg/rpmsg_ns.c
> @@ -0,0 +1,135 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) STMicroelectronics 2020 - All Rights Reserved
> + */
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include "rpmsg_internal.h"
> +
> +/**
> + * enum rpmsg_ns_flags - dynamic name service announcement flags
> + *
> + * @RPMSG_NS_CREATE: a new remote service was just created
> + * @RPMSG_NS_DESTROY: a known remote service was just destroyed
> + */
> +enum rpmsg_ns_flags {
> +	RPMSG_NS_CREATE		= 0,
> +	RPMSG_NS_DESTROY	= 1,
> +};
> +
> +/**
> + * struct rpmsg_ns_msg - dynamic name service announcement message
> + * @name: name of remote service that is published
> + * @addr: address of remote service that is published
> + * @flags: indicates whether service is created or destroyed
> + *
> + * This message is sent across to publish a new service, or announce
> + * about its removal. When we receive these messages, an appropriate
> + * rpmsg channel (i.e device) is created/destroyed. In turn, the ->probe()
> + * or ->remove() handler of the appropriate rpmsg driver will be invoked
> + * (if/as-soon-as one is registered).
> + */
> +struct rpmsg_ns_msg {
> +	char name[RPMSG_NAME_SIZE];
> +	__le32 addr;
> +	__le32 flags;

This is about to get moved to a header file [1] so that the virtualisation people
can use the same structures.  As such we can't just assume their type is __le32
and we can't move them here either.  I suggest to move this to
include/linux/rpmsg/virtio.h as Guennadi did.

[1]. https://patchwork.kernel.org/patch/11749285/

> +} __packed;
> +
> +/* Invoked when a name service announcement arrives */
> +static int rpmsg_ns_cb(struct rpmsg_device *rpdev, void *data, int len,
> +		       void *priv, u32 src)
> +{
> +	struct rpmsg_ns_msg *msg = data;
> +	struct rpmsg_device *newch;
> +	struct rpmsg_channel_info chinfo;
> +	struct device *dev = &rpdev->dev;
> +	unsigned int flags = le32_to_cpu(msg->flags);

I've been staring at this for a long time and I suspect you did too.

Can we assume that a name service is running on a virtio implementation?  It
certainly has been the case so far, and doing so would make this patchset a lot
more simple.  Otherwise we need to find a way to make this work without
losing flexibility, which will make things more complex.

What do you think?

> +	int ret;
> +
> +#if defined(CONFIG_DYNAMIC_DEBUG)
> +	dynamic_hex_dump("NS announcement: ", DUMP_PREFIX_NONE, 16, 1,
> +			 data, len, true);
> +#endif
> +
> +	if (len != sizeof(*msg)) {
> +		dev_err(dev, "malformed ns msg (%d)\n", len);
> +		return -EINVAL;
> +	}
> +
> +	/* Don't trust the remote processor for null terminating the name */
> +	msg->name[RPMSG_NAME_SIZE - 1] = '\0';
> +
> +	strncpy(chinfo.name, msg->name, sizeof(chinfo.name));
> +	chinfo.src = RPMSG_ADDR_ANY;
> +	chinfo.dst = le32_to_cpu(msg->addr);
> +
> +	dev_info(dev, "%sing channel %s addr 0x%x\n",
> +		 (flags & RPMSG_NS_DESTROY) ? "destroy" : "creat",
> +		 msg->name, chinfo.dst);
> +
> +	if (flags & RPMSG_NS_DESTROY) {
> +		ret = rpmsg_release_channel(rpdev, &chinfo);
> +		if (ret)
> +			dev_err(dev, "rpmsg_destroy_channel failed: %d\n", ret);
> +	} else {
> +		newch = rpmsg_create_channel(rpdev, &chinfo);
> +		if (!newch)
> +			dev_err(dev, "rpmsg_create_channel failed\n");
> +	}
> +
> +	return 0;
> +}
> +
> +static int rpmsg_ns_probe(struct rpmsg_device *rpdev)
> +{
> +	struct rpmsg_channel_info ns_chinfo;
> +	struct rpmsg_endpoint *ns_ept;
> +
> +	ns_chinfo.src = RPMSG_NS_ADDR;
> +	ns_chinfo.dst = RPMSG_NS_ADDR;
> +	strcpy(ns_chinfo.name, "name_service");
> +
> +	/*
> +	 * Create the NS announcement service endpoint associated to the RPMsg
> +	 * device. The endpoint will be automatically destroyed when the RPMsg
> +	 * device will be deleted.
> +	 */
> +	ns_ept = rpmsg_create_ept(rpdev, rpmsg_ns_cb, NULL, ns_chinfo);
> +	if (!ns_ept) {
> +		dev_err(&rpdev->dev, "failed to create the ns ept\n");
> +		return -ENOMEM;
> +	}
> +	rpdev->ept = ns_ept;
> +
> +	return 0;
> +}
> +
> +static struct rpmsg_driver rpmsg_ns_driver = {
> +	.drv.name = "rpmsg_ns",
> +	.probe = rpmsg_ns_probe,
> +};
> +
> +static int rpmsg_ns_init(void)
> +{
> +	int ret;
> +
> +	ret = register_rpmsg_driver(&rpmsg_ns_driver);
> +	if (ret < 0)
> +		pr_err("%s: Failed to register rpmsg driver\n", __func__);
> +
> +	return ret;
> +}
> +postcore_initcall(rpmsg_ns_init);
> +
> +static void rpmsg_ns_exit(void)
> +{
> +	unregister_rpmsg_driver(&rpmsg_ns_driver);
> +}
> +module_exit(rpmsg_ns_exit);
> +
> +MODULE_DESCRIPTION("Name service announcement rpmsg Driver");
> +MODULE_AUTHOR("Arnaud Pouliquen <arnaud.pouliquen@...com>");
> +MODULE_ALIAS("rpmsg_ns");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.17.1
> 

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