Re: [PATCH v2] rpmsg: add a description field

[Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>]

Hi Suman,

Sorry for the delay in replying...

On 8/28/19 11:37 PM, Suman Anna wrote:
> Hi Arnaud,
>
> On 8/27/19 8:58 AM, Arnaud Pouliquen wrote:
> > Hi Suman,
> >
> > On 8/16/19 1:14 AM, Suman Anna wrote:
> > > From: Ohad Ben-Cohen <ohad@xxxxxxxxxx>
> > >
> > > Add a new description field to the rpmsg bus infrastructure
> > > that can be passed onto the rpmsg client drivers for additional
> > > information. The current rpmsg bus client drivers need to have
> > > a fixed id_table for proper matching, this new field can allow
> > > flexibility for the client drivers (eg: like creating unique
> > > cdevs).
> > >
> > > The description field is published through an enhanced name
> > > service announcement message structure. The name service
> > > message processing logic is updated to maintain backward
> > > compatibility with the previous message structure.
> >
> > Could you give some concrete use cases associated with your need?.
> > I'm not sure I'm interpreting it correctly...
>
> I have a generic rpmsg-rpc driver that allows userspace to execute any
> of a set of remote functions provided by a service. And we can have the
> same set of functions exported from different rprocs, or different
> services presenting different sets of functions. And the same service is
> used by multiple applications through their own fds. I use the desc
> field to differentiate between the services.

Thanks, this help me to understand the need. Very interesting feature, 
do you plan to upstream it? :)

> > Your patch seems to me a way to create a kind of sub-service. Why not
> > simply concatenate this in the name services, i.e creating several name
> > services ("service-0", "service-1"...)?
>
> Every-time a new service is added, it requires a driver update adding
> the new service name to the compatible list, or a corresponding udev
> rule. It is really upto the individual rpmsg driver as to how it uses
> the desc field, so it is optional as far as a rpmsg driver is concerned
> (since this didn't exist previously, and so all existing drivers will
> continue to work as before).

> > Regarding your implementation, the descriptor field seems used to:
> > - instantiate a rpmsg service
> > - retrieve the instance from the userland based on the descriptor.
> >
> > What not just use this descriptor to provide information to userland via
> > sysfs, but not use it as a criteria to find the rpmsg device?
>
> The rpmsg device logic for actually probing a rpmsg driver still relies
> on the name field. I added the additional check against desc to just
> ensure that there are no name clashes on the desc field. Do you have any
> concerns with this check?

First be sure that I understand and agree with the need to have a more 
dynamic way of managing the services. My concerns is more about the way 
to implement it. In my view the need corresponds to the introduction of 
a kind of sub-services to instantiate a service, plus a way to identify 
the sub service. Adding a second field is one solution, but seems to me 
a duplication of the service name. And i have also in mind the OpenAMP 
lib that should support this extra field, with footprint impact.

Xiang Xiao from Xiaomi company proposed an alternative patch a few 
months ago: https://patchwork.kernel.org/patch/10791741/.
The idea is let the driver to check the device match. In this case it 
could support "dynamic" name service. A service name could be a 
concatenation of the basic service name + a descriptor.

Could this patch answer to your need? IMHO, I would prefer this solution 
that gives advantage to not extend the message protocol for NS announcement.

Regards,
Arnaud

> > In this case you can use the remote endpoint address(dst addr) to
> > instantiate the service. The descriptor field could just be an
> > information to help application to retrieve the good instance of the
> > service.
> >
> > > Based on an initial patch from Ohad Ben-Cohen.
> > >
> > > Signed-off-by: Ohad Ben-Cohen <ohad@xxxxxxxxxx>
> > > [s-anna@xxxxxx: forward port, add sysfs documentation, fixup qcom
> > > drivers]
> > > Signed-off-by: Suman Anna <s-anna@xxxxxx>
> > > [t-kristo@xxxxxx: reworked to support both rpmsg with/without the desc
> > > field]
> > > Signed-off-by: Tero Kristo <t-kristo@xxxxxx>
> > > ---
> > > v2:
> > >    - Localized the desc match check to virtio-rpmsg-bus
> > >    - Enforced NULL termination of desc similar to name
> > > v1: https://patchwork.kernel.org/patch/11087717/
> > >    Documentation/ABI/testing/sysfs-bus-rpmsg | 29 ++++++++++
> > >    drivers/rpmsg/qcom_glink_native.c         |  1 +
> > >    drivers/rpmsg/qcom_smd.c                  |  1 +
> > >    drivers/rpmsg/rpmsg_char.c                |  1 +
> > >    drivers/rpmsg/rpmsg_core.c                |  2 +
> > >    drivers/rpmsg/virtio_rpmsg_bus.c          | 67 +++++++++++++++++++++--
> > >    drivers/soc/qcom/wcnss_ctrl.c             |  1 +
> > >    include/linux/rpmsg.h                     |  4 ++
> > >    8 files changed, 101 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-bus-rpmsg
> > > b/Documentation/ABI/testing/sysfs-bus-rpmsg
> > > index 990fcc420935..7f1b09ecc64d 100644
> > > --- a/Documentation/ABI/testing/sysfs-bus-rpmsg
> > > +++ b/Documentation/ABI/testing/sysfs-bus-rpmsg
> > > @@ -93,3 +93,32 @@ Description:
> > >            This sysfs entry allows the rpmsg driver for a rpmsg device
> > >            to be specified which will override standard OF, ID table
> > >            and name matching.
> > > +
> > > +What:        /sys/bus/rpmsg/devices/.../desc
> > > +Date:        August 2019
> > > +KernelVersion:    5.4
> > > +Contact:    Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> > > +Description:
> > > +        Every rpmsg device is a communication channel with a remote
> > > +        processor. Channels are identified by a textual name (see
> > > +        /sys/bus/rpmsg/devices/.../name above) and have a local
> > > +        ("source") rpmsg address, and remote ("destination") rpmsg
> > > +        address.
> > > +
> > > +        A channel is first created when an entity, whether local
> > > +        or remote, starts listening on it for messages (and is thus
> > > +        called an rpmsg server). When that happens, a "name service"
> > > +        announcement is sent to the other processor, in order to let
> > > +        it know about the creation of the channel (this way remote
> > > +        clients know they can start sending messages).
> > > +
> > > +        The listening entity (or client) which communicates with a
> > > +        remote processor is referred as rpmsg driver. The rpmsg device
> > > +        and rpmsg driver are matched based on rpmsg device name (see
> > > +        /sys/bus/rpmsg/devices/.../name above) and rpmsg driver ID
> > > table.
> > > +
> > > +        This sysfs entry contains an additional optional description of
> > > +        the rpmsg device that can be optionally included as part of the
> > > +        "name service" announcement. This description is then passed on
> > > +        to the corresponding rpmsg drivers to further distinguish
> > > multiple
> > > +        devices associated with the same rpmsg driver.
> > > diff --git a/drivers/rpmsg/qcom_glink_native.c
> > > b/drivers/rpmsg/qcom_glink_native.c
> > > index f46c787733e8..cfdabddc15ac 100644
> > > --- a/drivers/rpmsg/qcom_glink_native.c
> > > +++ b/drivers/rpmsg/qcom_glink_native.c
> > > @@ -1456,6 +1456,7 @@ static void qcom_glink_rx_close(struct
> > > qcom_glink *glink, unsigned int rcid)
> > >            strncpy(chinfo.name, channel->name, sizeof(chinfo.name));
> > >            chinfo.src = RPMSG_ADDR_ANY;
> > >            chinfo.dst = RPMSG_ADDR_ANY;
> > > +        chinfo.desc[0] = '\0';
> > >              rpmsg_unregister_device(glink->dev, &chinfo);
> > >        }
> > > diff --git a/drivers/rpmsg/qcom_smd.c b/drivers/rpmsg/qcom_smd.c
> > > index 4abbeea782fa..7cd6b9c47065 100644
> > > --- a/drivers/rpmsg/qcom_smd.c
> > > +++ b/drivers/rpmsg/qcom_smd.c
> > > @@ -1307,6 +1307,7 @@ static void qcom_channel_state_worker(struct
> > > work_struct *work)
> > >            strncpy(chinfo.name, channel->name, sizeof(chinfo.name));
> > >            chinfo.src = RPMSG_ADDR_ANY;
> > >            chinfo.dst = RPMSG_ADDR_ANY;
> > > +        chinfo.desc[0] = '\0';
> > >            rpmsg_unregister_device(&edge->dev, &chinfo);
> > >            channel->registered = false;
> > >            spin_lock_irqsave(&edge->channels_lock, flags);
> > > diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> > > index eea5ebbb5119..4bd91445a2fd 100644
> > > --- a/drivers/rpmsg/rpmsg_char.c
> > > +++ b/drivers/rpmsg/rpmsg_char.c
> > > @@ -442,6 +442,7 @@ static long rpmsg_ctrldev_ioctl(struct file *fp,
> > > unsigned int cmd,
> > >        chinfo.name[RPMSG_NAME_SIZE-1] = '\0';
> > >        chinfo.src = eptinfo.src;
> > >        chinfo.dst = eptinfo.dst;
> > > +    chinfo.desc[0] = '\0';
> > >          return rpmsg_eptdev_create(ctrldev, chinfo);
> > >    };
> > > diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> > > index ea88fd4e2a6e..ba0f2c1a7fa4 100644
> > > --- a/drivers/rpmsg/rpmsg_core.c
> > > +++ b/drivers/rpmsg/rpmsg_core.c
> > > @@ -365,6 +365,7 @@ static DEVICE_ATTR_RW(field)
> > >      /* for more info, see Documentation/ABI/testing/sysfs-bus-rpmsg */
> > >    rpmsg_show_attr(name, id.name, "%s\n");
> > > +rpmsg_show_attr(desc, desc, "%s\n");
> > >    rpmsg_show_attr(src, src, "0x%x\n");
> > >    rpmsg_show_attr(dst, dst, "0x%x\n");
> > >    rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
> > > @@ -386,6 +387,7 @@ static DEVICE_ATTR_RO(modalias);
> > >      static struct attribute *rpmsg_dev_attrs[] = {
> > >        &dev_attr_name.attr,
> > > +    &dev_attr_desc.attr,
> > >        &dev_attr_modalias.attr,
> > >        &dev_attr_dst.attr,
> > >        &dev_attr_src.attr,
> > > diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c
> > > b/drivers/rpmsg/virtio_rpmsg_bus.c
> > > index 5d3685bd76a2..b42277cd7759 100644
> > > --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> > > +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> > > @@ -110,6 +110,23 @@ struct rpmsg_ns_msg {
> > >        u32 flags;
> > >    } __packed;
> > >    +/**
> > > + * struct rpmsg_ns_msg_ext - dynamic name service announcement
> > > message v2
> > > + * @name: name of remote service that is published
> > > + * @desc: description of remote service
> > > + * @addr: address of remote service that is published
> > > + * @flags: indicates whether service is created or destroyed
> > > + *
> > > + * Interchangeable nameservice message with rpmsg_ns_msg. This one has
> > > + * the addition of the desc field for extra flexibility.
> > > + */
> > > +struct rpmsg_ns_msg_ext {
> > > +    char name[RPMSG_NAME_SIZE];
> > > +    char desc[RPMSG_NAME_SIZE];
> > > +    u32 addr;
> > > +    u32 flags;
> > > +} __packed;
> > > +
> > >    /**
> > >     * enum rpmsg_ns_flags - dynamic name service announcement flags
> > >     *
> > > @@ -384,6 +401,24 @@ static void virtio_rpmsg_release_device(struct
> > > device *dev)
> > >        kfree(vch);
> > >    }
> > >    +static int virtio_rpmsg_desc_match(struct device *dev, void *data)
> > > +{
> > > +    struct rpmsg_channel_info *chinfo = data;
> > > +    struct rpmsg_device *rpdev = to_rpmsg_device(dev);
> > > +
> > > +    if (!*chinfo->desc)
> > > +        return 0;
> > > +
> > > +    if (strncmp(chinfo->name, rpdev->id.name, RPMSG_NAME_SIZE))
> > > +        return 0;
> > > +
> > > +    if (strncmp(chinfo->desc, rpdev->desc, RPMSG_NAME_SIZE))
> > > +        return 0;
> > > +
> > > +    /* found a match ! */
> > > +    return 1;
> > > +}
> > > +
> > >    /*
> > >     * create an rpmsg channel using its name and address info.
> > >     * this function will be used to create both static and dynamic
> > > @@ -407,6 +442,15 @@ static struct rpmsg_device
> > > *rpmsg_create_channel(struct virtproc_info *vrp,
> > >            return NULL;
> > >        }
> > >    +    tmp = device_find_child(dev, chinfo, virtio_rpmsg_desc_match);
> > > +    if (tmp) {
> > > +        /* decrement the matched device's refcount back */
> > > +        put_device(tmp);
> > > +        dev_err(dev, "channel %s:%x:%x failed, desc '%s' already
> > > exists\n",
> > > +            chinfo->name, chinfo->src, chinfo->dst, chinfo->desc);
> > > +        return NULL;
> > > +    }
> > > +
> > >        vch = kzalloc(sizeof(*vch), GFP_KERNEL);
> > >        if (!vch)
> > >            return NULL;
> > > @@ -419,6 +463,7 @@ static struct rpmsg_device
> > > *rpmsg_create_channel(struct virtproc_info *vrp,
> > >        rpdev->src = chinfo->src;
> > >        rpdev->dst = chinfo->dst;
> > >        rpdev->ops = &virtio_rpmsg_ops;
> > > +    strncpy(rpdev->desc, chinfo->desc, RPMSG_NAME_SIZE);
> > >          /*
> > >         * rpmsg server channels has predefined local address (for now),
> > > @@ -816,18 +861,30 @@ 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_ns_msg_ext *msg_ext = data;
> > >        struct rpmsg_device *newch;
> > >        struct rpmsg_channel_info chinfo;
> > >        struct virtproc_info *vrp = priv;
> > >        struct device *dev = &vrp->vdev->dev;
> > >        int ret;
> > > +    u32 addr;
> > > +    u32 flags;
> > >      #if defined(CONFIG_DYNAMIC_DEBUG)
> > >        dynamic_hex_dump("NS announcement: ", DUMP_PREFIX_NONE, 16, 1,
> > >                 data, len, true);
> > >    #endif
> > >    -    if (len != sizeof(*msg)) {
> > > +    if (len == sizeof(*msg)) {
> > > +        addr = msg->addr;
> > > +        flags = msg->flags;
> > > +        chinfo.desc[0] = '\0';
> > > +    } else if (len == sizeof(*msg_ext)) {
> > > +        addr = msg_ext->addr;
> > > +        flags = msg_ext->flags;
> > > +        msg_ext->desc[RPMSG_NAME_SIZE - 1] = '\0';
> > > +        strncpy(chinfo.desc, msg_ext->desc, sizeof(chinfo.desc));
> > > +    } else {
> > >            dev_err(dev, "malformed ns msg (%d)\n", len);
> > >            return -EINVAL;
> > >        }
> > > @@ -847,14 +904,14 @@ static int rpmsg_ns_cb(struct rpmsg_device
> > > *rpdev, void *data, int len,
> > >        msg->name[RPMSG_NAME_SIZE - 1] = '\0';
> > >          dev_info(dev, "%sing channel %s addr 0x%x\n",
> > > -         msg->flags & RPMSG_NS_DESTROY ? "destroy" : "creat",
> > > -         msg->name, msg->addr);
> > > +         flags & RPMSG_NS_DESTROY ? "destroy" : "creat",
> > > +         msg->name, addr);
> > >          strncpy(chinfo.name, msg->name, sizeof(chinfo.name));
> > >        chinfo.src = RPMSG_ADDR_ANY;
> > > -    chinfo.dst = msg->addr;
> > > +    chinfo.dst = addr;
> > >    -    if (msg->flags & RPMSG_NS_DESTROY) {
> > > +    if (flags & RPMSG_NS_DESTROY) {
> > >            ret = rpmsg_unregister_device(&vrp->vdev->dev, &chinfo);
> > >            if (ret)
> > >                dev_err(dev, "rpmsg_destroy_channel failed: %d\n", ret);
> > > diff --git a/drivers/soc/qcom/wcnss_ctrl.c
> > > b/drivers/soc/qcom/wcnss_ctrl.c
> > > index e5c68051fb17..ad9f28dc13f1 100644
> > > --- a/drivers/soc/qcom/wcnss_ctrl.c
> > > +++ b/drivers/soc/qcom/wcnss_ctrl.c
> > > @@ -276,6 +276,7 @@ struct rpmsg_endpoint
> > > *qcom_wcnss_open_channel(void *wcnss, const char *name, rp
> > >        strscpy(chinfo.name, name, sizeof(chinfo.name));
> > >        chinfo.src = RPMSG_ADDR_ANY;
> > >        chinfo.dst = RPMSG_ADDR_ANY;
> > > +    chinfo.desc[0] = '\0';
> > >          return rpmsg_create_ept(_wcnss->channel->rpdev, cb, priv,
> > > chinfo);
>
> > There is another way to create a service, by registering an RPMsg
> > drivers (e.g.
> > https://elixir.bootlin.com/linux/v5.3-rc6/source/samples/rpmsg/rpmsg_client_sample.c)
>
> I am not sure I understand, you obviously need a rpmsg driver for a
> rpmsg device to probe.
>
> > In this case the descriptor can not be used, right?
> > To be compliant probably need to extend the rpmsg_device_id struct...
>
> As I mentioned above, it is optional for backward compatibility, and the
> rpmsg client sample doesn't have any use for it atm, even if a firmware
> publishes a desc field alongside the "rpmsg-client-sample" name. That is
> why, I haven't extended the rpmsg_device_id.
>
> regards
> Suman
>
> > Regards,
> > Arnaud
> > >    }
> > > diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> > > index 9fe156d1c018..436faf04ba1c 100644
> > > --- a/include/linux/rpmsg.h
> > > +++ b/include/linux/rpmsg.h
> > > @@ -28,11 +28,13 @@ struct rpmsg_endpoint_ops;
> > >    /**
> > >     * struct rpmsg_channel_info - channel info representation
> > >     * @name: name of service
> > > + * @desc: description of service
> > >     * @src: local address
> > >     * @dst: destination address
> > >     */
> > >    struct rpmsg_channel_info {
> > >        char name[RPMSG_NAME_SIZE];
> > > +    char desc[RPMSG_NAME_SIZE];
> > >        u32 src;
> > >        u32 dst;
> > >    };
> > > @@ -42,6 +44,7 @@ struct rpmsg_channel_info {
> > >     * @dev: the device struct
> > >     * @id: device id (used to match between rpmsg drivers and devices)
> > >     * @driver_override: driver name to force a match
> > > + * @desc: description of remote service
> > >     * @src: local address
> > >     * @dst: destination address
> > >     * @ept: the rpmsg endpoint of this channel
> > > @@ -51,6 +54,7 @@ struct rpmsg_device {
> > >        struct device dev;
> > >        struct rpmsg_device_id id;
> > >        char *driver_override;
> > > +    char desc[RPMSG_NAME_SIZE];
> > >        u32 src;
> > >        u32 dst;
> > >        struct rpmsg_endpoint *ept;