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Message-ID: <20250516120708.GA10474@wendao-VirtualBox>
Date: Fri, 16 May 2025 20:07:08 +0800
From: Dawei Li <dawei.li@...ux.dev>
To: Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: andersson@...nel.org, linux-remoteproc@...r.kernel.org,
linux-kernel@...r.kernel.org, set_pte_at@...look.com,
dawei.li@...ux.dev
Subject: Re: [PATCH v2 1/3] rpmsg: char: Reuse eptdev logic for anon device
Hi Mathieu,
Thanks for reviewing.
On Thu, May 15, 2025 at 02:24:04PM -0600, Mathieu Poirier wrote:
> Hi,
>
> On Fri, May 09, 2025 at 11:59:25PM +0800, Dawei Li wrote:
> > Current uAPI implementation for rpmsg ctrl & char device manipulation is
> > abstracted in procedures below:
> >
> > Current uAPI implementation for rpmsg ctrl & char device manipulation is
> > abstracted in procedures below:
> > - fd = open("/dev/rpmsg_ctrlX")
> > - ioctl(fd, RPMSG_CREATE_EPT_IOCTL, &info); /dev/rpmsgY devnode is
> > generated.
> > - fd_ep = open("/dev/rpmsgY", O_RDWR)
> > - operations on fd_ep(write, read, poll ioctl)
> > - ioctl(fd_ep, RPMSG_DESTROY_EPT_IOCTL)
> > - close(fd_ep)
> > - close(fd)
> >
> > This /dev/rpmsgY abstraction is less favorable for:
> > - Performance issue: It's time consuming for some operations are
> > invovled:
> > - Device node creation.
> > Depends on specific config, especially CONFIG_DEVTMPFS, the overall
> > overhead is based on coordination between DEVTMPFS and userspace
> > tools such as udev and mdev.
> >
> > - Extra kernel-space switch cost.
> >
> > - Other major costs brought by heavy-weight logic like device_add().
> >
> > - /dev/rpmsgY node can be opened only once. It doesn't make much sense
> > that a dynamically created device node can be opened only once.
> >
> > - For some container application such as docker, a client can't access
> > host's dev unless specified explicitly. But in case of /dev/rpmsgY, which
> > is generated dynamically and whose existence is unknown for clients in
> > advance, this uAPI based on device node doesn't fit well.
> >
> > An anon inode based approach is introduced to address the issues above.
> > Rather than generating device node and opening it, rpmsg code just make
> > a anon inode representing eptdev and return the fd to userspace.
>
> Please change occurences of "anon" for "anonyous". "Anon" was used to avoid
> writing "anonymous" all the time in the code, but description should not use the
> shorthand. In the title, this patch and all other patches.
Acked.
>
> >
> > The legacy abstraction based on struct dev and struct cdev is honored
> > for:
> > - Avoid legacy uAPI break(RPMSG_CREATE_EPT_IOCTL)
> > - Reuse existing logic:
> > -- dev_err() and friends.
> > -- Life cycle management of struct device.
> >
> > Signed-off-by: Dawei Li <dawei.li@...ux.dev>
> > ---
> > drivers/rpmsg/rpmsg_char.c | 80 ++++++++++++++++++++++++++------------
> > 1 file changed, 56 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> > index eec7642d2686..5b2a883d6236 100644
> > --- a/drivers/rpmsg/rpmsg_char.c
> > +++ b/drivers/rpmsg/rpmsg_char.c
> > @@ -91,7 +91,8 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
> > /* wake up any blocked readers */
> > wake_up_interruptible(&eptdev->readq);
> >
> > - cdev_device_del(&eptdev->cdev, &eptdev->dev);
> > + if (eptdev->dev.devt)
> > + cdev_device_del(&eptdev->cdev, &eptdev->dev);
> > put_device(&eptdev->dev);
> >
> > return 0;
> > @@ -132,21 +133,17 @@ static int rpmsg_ept_flow_cb(struct rpmsg_device *rpdev, void *priv, bool enable
> > return 0;
> > }
> >
> > -static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
> > +static int __rpmsg_eptdev_open(struct rpmsg_eptdev *eptdev)
> > {
> > - struct rpmsg_eptdev *eptdev = cdev_to_eptdev(inode->i_cdev);
> > struct rpmsg_endpoint *ept;
> > struct rpmsg_device *rpdev = eptdev->rpdev;
> > struct device *dev = &eptdev->dev;
> >
> > - mutex_lock(&eptdev->ept_lock);
> > if (eptdev->ept) {
> > - mutex_unlock(&eptdev->ept_lock);
> > return -EBUSY;
> > }
> >
> > if (!eptdev->rpdev) {
> > - mutex_unlock(&eptdev->ept_lock);
> > return -ENETRESET;
> > }
> >
> > @@ -164,21 +161,32 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
> > if (!ept) {
> > dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
> > put_device(dev);
> > - mutex_unlock(&eptdev->ept_lock);
> > return -EINVAL;
> > }
> >
> > ept->flow_cb = rpmsg_ept_flow_cb;
> > eptdev->ept = ept;
> > - filp->private_data = eptdev;
> > - mutex_unlock(&eptdev->ept_lock);
> >
> > return 0;
> > }
> >
> > -static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
> > +static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
> > {
> > struct rpmsg_eptdev *eptdev = cdev_to_eptdev(inode->i_cdev);
> > + int ret;
> > +
> > + mutex_lock(&eptdev->ept_lock);
> > + ret = __rpmsg_eptdev_open(eptdev);
> > + if (!ret)
> > + filp->private_data = eptdev;
> > + mutex_unlock(&eptdev->ept_lock);
> > +
> > + return ret;
> > +}
> > +
> > +static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
> > +{
> > + struct rpmsg_eptdev *eptdev = filp->private_data;
> > struct device *dev = &eptdev->dev;
> >
> > /* Close the endpoint, if it's not already destroyed by the parent */
> > @@ -400,12 +408,13 @@ static void rpmsg_eptdev_release_device(struct device *dev)
> > struct rpmsg_eptdev *eptdev = dev_to_eptdev(dev);
> >
> > ida_free(&rpmsg_ept_ida, dev->id);
> > - ida_free(&rpmsg_minor_ida, MINOR(eptdev->dev.devt));
> > + if (eptdev->dev.devt)
> > + ida_free(&rpmsg_minor_ida, MINOR(eptdev->dev.devt));
> > kfree(eptdev);
> > }
> >
> > -static struct rpmsg_eptdev *rpmsg_chrdev_eptdev_alloc(struct rpmsg_device *rpdev,
> > - struct device *parent)
> > +static struct rpmsg_eptdev *__rpmsg_chrdev_eptdev_alloc(struct rpmsg_device *rpdev,
> > + struct device *parent, bool cdev)
>
>
> I would simply rename this rpmsg_eptdev_alloc() and then use is in
> rpmsg_chrdev_eptdev_alloc() and rpmsg_anonynous_eptdev_alloc()
Agreed. rpmsg_eptdev_alloc() is much better.
>
> > {
> > struct rpmsg_eptdev *eptdev;
> > struct device *dev;
> > @@ -428,33 +437,50 @@ static struct rpmsg_eptdev *rpmsg_chrdev_eptdev_alloc(struct rpmsg_device *rpdev
> > dev->groups = rpmsg_eptdev_groups;
> > dev_set_drvdata(dev, eptdev);
> >
> > - cdev_init(&eptdev->cdev, &rpmsg_eptdev_fops);
> > - eptdev->cdev.owner = THIS_MODULE;
> > + if (cdev) {
> > + cdev_init(&eptdev->cdev, &rpmsg_eptdev_fops);
> > + eptdev->cdev.owner = THIS_MODULE;
> > + }
> >
> > return eptdev;
> > }
> >
> > -static int rpmsg_chrdev_eptdev_add(struct rpmsg_eptdev *eptdev, struct rpmsg_channel_info chinfo)
> > +static struct rpmsg_eptdev *rpmsg_chrdev_eptdev_alloc(struct rpmsg_device *rpdev,
> > + struct device *parent)
> > +{
> > + return __rpmsg_chrdev_eptdev_alloc(rpdev, parent, true);
> > +}
> > +
> > +static int __rpmsg_chrdev_eptdev_add(struct rpmsg_eptdev *eptdev,
> > + struct rpmsg_channel_info chinfo, bool cdev)
>
> Same here, rpmsg_eptdev_add()
Acked.
All the issues above, including those for patch 2/3, will be fixed in
V3.
Thanks,
Dawei
>
> > {
> > struct device *dev = &eptdev->dev;
> > int ret;
> >
> > eptdev->chinfo = chinfo;
> >
> > - ret = ida_alloc_max(&rpmsg_minor_ida, RPMSG_DEV_MAX - 1, GFP_KERNEL);
> > - if (ret < 0)
> > - goto free_eptdev;
> > - dev->devt = MKDEV(MAJOR(rpmsg_major), ret);
> > + if (cdev) {
> > + ret = ida_alloc_max(&rpmsg_minor_ida, RPMSG_DEV_MAX - 1, GFP_KERNEL);
> > + if (ret < 0)
> > + goto free_eptdev;
> >
> > + dev->devt = MKDEV(MAJOR(rpmsg_major), ret);
> > + }
> > +
> > + /* Anon inode device still need dev name for dev_err() and friends */
> > ret = ida_alloc(&rpmsg_ept_ida, GFP_KERNEL);
> > if (ret < 0)
> > goto free_minor_ida;
> > dev->id = ret;
> > dev_set_name(dev, "rpmsg%d", ret);
> >
> > - ret = cdev_device_add(&eptdev->cdev, &eptdev->dev);
> > - if (ret)
> > - goto free_ept_ida;
> > + ret = 0;
> > +
> > + if (cdev) {
> > + ret = cdev_device_add(&eptdev->cdev, &eptdev->dev);
> > + if (ret)
> > + goto free_ept_ida;
> > + }
> >
> > /* We can now rely on the release function for cleanup */
> > dev->release = rpmsg_eptdev_release_device;
> > @@ -464,7 +490,8 @@ static int rpmsg_chrdev_eptdev_add(struct rpmsg_eptdev *eptdev, struct rpmsg_cha
> > free_ept_ida:
> > ida_free(&rpmsg_ept_ida, dev->id);
> > free_minor_ida:
> > - ida_free(&rpmsg_minor_ida, MINOR(dev->devt));
> > + if (cdev)
> > + ida_free(&rpmsg_minor_ida, MINOR(dev->devt));
> > free_eptdev:
> > put_device(dev);
> > kfree(eptdev);
> > @@ -472,6 +499,11 @@ static int rpmsg_chrdev_eptdev_add(struct rpmsg_eptdev *eptdev, struct rpmsg_cha
> > return ret;
> > }
> >
> > +static int rpmsg_chrdev_eptdev_add(struct rpmsg_eptdev *eptdev, struct rpmsg_channel_info chinfo)
> > +{
> > + return __rpmsg_chrdev_eptdev_add(eptdev, chinfo, true);
> > +}
> > +
> > int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent,
> > struct rpmsg_channel_info chinfo)
> > {
> > --
> > 2.25.1
> >
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