Date:   Fri, 21 Feb 2020 17:45:43 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Vitor Soares <Vitor.Soares@...opsys.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        "corbet@....net" <corbet@....net>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "bbrezillon@...nel.org" <bbrezillon@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>
Subject: Re: [PATCH v3 3/5] i3c: master: add i3c_for_each_dev helper

On Fri, 21 Feb 2020 17:44:28 +0100
Boris Brezillon <boris.brezillon@...labora.com> wrote:

> On Fri, 21 Feb 2020 13:59:11 +0100
> Boris Brezillon <boris.brezillon@...labora.com> wrote:
> 
> > On Fri, 21 Feb 2020 12:52:29 +0100
> > Greg KH <gregkh@...uxfoundation.org> wrote:
> >   
> > > On Fri, Feb 21, 2020 at 11:47:22AM +0000, Vitor Soares wrote:    
> > > > Hi Greg,
> > > > 
> > > > From: Greg KH <gregkh@...uxfoundation.org>
> > > > Date: Wed, Feb 19, 2020 at 07:35:48
> > > >       
> > > > > On Wed, Feb 19, 2020 at 01:20:41AM +0100, Vitor Soares wrote:      
> > > > > > Introduce i3c_for_each_dev(), an i3c device iterator for use by i3cdev.
> > > > > > 
> > > > > > Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> > > > > > ---
> > > > > >  drivers/i3c/internals.h |  1 +
> > > > > >  drivers/i3c/master.c    | 12 ++++++++++++
> > > > > >  2 files changed, 13 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/i3c/internals.h b/drivers/i3c/internals.h
> > > > > > index bc062e8..a6deedf 100644
> > > > > > --- a/drivers/i3c/internals.h
> > > > > > +++ b/drivers/i3c/internals.h
> > > > > > @@ -24,4 +24,5 @@ int i3c_dev_enable_ibi_locked(struct i3c_dev_desc *dev);
> > > > > >  int i3c_dev_request_ibi_locked(struct i3c_dev_desc *dev,
> > > > > >  			       const struct i3c_ibi_setup *req);
> > > > > >  void i3c_dev_free_ibi_locked(struct i3c_dev_desc *dev);
> > > > > > +int i3c_for_each_dev(void *data, int (*fn)(struct device *, void *));
> > > > > >  #endif /* I3C_INTERNAL_H */
> > > > > > diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> > > > > > index 21c4372..8e22da2 100644
> > > > > > --- a/drivers/i3c/master.c
> > > > > > +++ b/drivers/i3c/master.c
> > > > > > @@ -2640,6 +2640,18 @@ void i3c_dev_free_ibi_locked(struct i3c_dev_desc *dev)
> > > > > >  	dev->ibi = NULL;
> > > > > >  }
> > > > > >  
> > > > > > +int i3c_for_each_dev(void *data, int (*fn)(struct device *, void *))
> > > > > > +{
> > > > > > +	int res;
> > > > > > +
> > > > > > +	mutex_lock(&i3c_core_lock);
> > > > > > +	res = bus_for_each_dev(&i3c_bus_type, NULL, data, fn);
> > > > > > +	mutex_unlock(&i3c_core_lock);      
> > > > > 
> > > > > Ick, why the lock?  Are you _sure_ you need that?  The core should
> > > > > handle any list locking issues here, right?      
> > > > 
> > > > I want to make sure that no new devices (eg: Hot-Join capable device) are 
> > > > added during this iteration and after this call, each new device will 
> > > > release a bus notification.
> > > >       
> > > > > 
> > > > > I don't see bus-specific-locks around other subsystem functions that do
> > > > > this (like usb_for_each_dev).      
> > > > 
> > > > I based in I2C use case.      
> > > 
> > > Check to see if this is really needed, for some reason I doubt it...    
> > 
> > Can we please try the spidev approach before fixing those problems. None
> > of that would be needed if we declare the i3cdev driver as a regular
> > i3c_device_driver and let user space bind devices it wants to expose
> > through the sysfs interface. As I said earlier, we even have all the
> > pieces we need to automate that using a udev rule, and the resulting
> > patchset would be 'less invasive'/simpler for pretty much the same
> > result.  
> 
> So, I went ahead and implemented it the way I suggest. The diffstat is
> not representative here (though it's still in favor of this new version)
> since I also changed the way we expose/handle SDR transfers. What's
> most important IMO is the fact that
> 
> * we no longer need to access the internal I3C API
> * we no longer need to care about transitions between i3cdev and
>   other drivers (the core guarantees that a device is always bound to at
>   most one driver)
> * the registration/unregistration procedure is simplified

Forgot to mention that

* Patch 1-3 are no longer required

> 
> Not all problems have been addressed (we still need to put a limit on
> the number of xfers and the max size per transfer we allow, and
> probably plenty of other things pointed by Greg, Arnd and others), but
> I'd really like to start from there for the next version.
> 
> --->8---  
> From a344e3c51db4e414e4ec6007c001c32afa954a82 Mon Sep 17 00:00:00 2001
> From: Vitor Soares <Vitor.Soares@...opsys.com>
> Date: Wed, 19 Feb 2020 01:20:42 +0100
> Subject: [PATCH] i3c: add i3cdev module to expose i3c dev in /dev
> 
> This patch adds user mode support to I3C SDR transfers.
> 
> The module is based on spidev with the follow features:
>   - Dynamically allocate the char device Major number.
>   - Expose SDR (Single Data Rate) transfers
> 
> Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> ---
>  drivers/i3c/Kconfig             |  15 ++
>  drivers/i3c/Makefile            |   1 +
>  drivers/i3c/i3cdev.c            | 324 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/i3c/i3cdev.h |  38 ++++
>  4 files changed, 378 insertions(+)
>  create mode 100644 drivers/i3c/i3cdev.c
>  create mode 100644 include/uapi/linux/i3c/i3cdev.h
> 
> diff --git a/drivers/i3c/Kconfig b/drivers/i3c/Kconfig
> index 30a441506f61..01642768ab5f 100644
> --- a/drivers/i3c/Kconfig
> +++ b/drivers/i3c/Kconfig
> @@ -20,5 +20,20 @@ menuconfig I3C
>  	  will be called i3c.
>  
>  if I3C
> +
> +config I3CDEV
> +	tristate "I3C device interface"
> +	depends on I3C
> +	help
> +	  Say Y here to use i3c-* device files, usually found in the /dev
> +	  directory on your system.  They make it possible to have user-space
> +	  programs use the I3C devices.
> +
> +	  This support is also available as a module.  If so, the module
> +	  will be called i3cdev.
> +
> +	  Note that this application programming interface is EXPERIMENTAL
> +	  and hence SUBJECT TO CHANGE WITHOUT NOTICE while it stabilizes.
> +
>  source "drivers/i3c/master/Kconfig"
>  endif # I3C
> diff --git a/drivers/i3c/Makefile b/drivers/i3c/Makefile
> index 11982efbc6d9..606d422841b2 100644
> --- a/drivers/i3c/Makefile
> +++ b/drivers/i3c/Makefile
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
>  i3c-y				:= device.o master.o
>  obj-$(CONFIG_I3C)		+= i3c.o
> +obj-$(CONFIG_I3CDEV)		+= i3cdev.o
>  obj-$(CONFIG_I3C)		+= master/
> diff --git a/drivers/i3c/i3cdev.c b/drivers/i3c/i3cdev.c
> new file mode 100644
> index 000000000000..2b408a446ab6
> --- /dev/null
> +++ b/drivers/i3c/i3cdev.c
> @@ -0,0 +1,324 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2020 Synopsys, Inc. and/or its affiliates.
> + *
> + * Author: Vitor Soares <soares@...opsys.com>
> + */
> +
> +#include <linux/cdev.h>
> +#include <linux/compat.h>
> +#include <linux/device.h>
> +#include <linux/fs.h>
> +#include <linux/i3c/device.h>
> +#include <linux/init.h>
> +#include <linux/jiffies.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/notifier.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#include <uapi/linux/i3c/i3cdev.h>
> +
> +#define MAX_I3CDEV_DEVS (MINORMASK + 1)
> +
> +struct i3cdev_data {
> +	struct i3c_device *i3c;
> +	struct device *dev;
> +	struct cdev cdev;
> +	dev_t devt;
> +};
> +
> +static DEFINE_IDA(i3cdev_ida);
> +static dev_t i3cdev_first_chrdev;
> +
> +static ssize_t
> +i3cdev_read(struct file *file, char __user *buf, size_t count, loff_t *f_pos)
> +{
> +	struct i3cdev_data *i3cdev = file->private_data;
> +	struct i3c_device *i3c = i3cdev->i3c;
> +	struct i3c_priv_xfer xfers = {
> +		.rnw = true,
> +		.len = count,
> +	};
> +	char *tmp;
> +	int ret;
> +
> +	tmp = kzalloc(count, GFP_KERNEL);
> +	if (!tmp)
> +		return -ENOMEM;
> +
> +	xfers.data.in = tmp;
> +
> +	dev_dbg(i3cdev->dev, "Reading %zu bytes.\n", count);
> +
> +	ret = i3c_device_do_priv_xfers(i3c, &xfers, 1);
> +	if (!ret)
> +		ret = copy_to_user(buf, tmp, xfers.len) ? -EFAULT : xfers.len;
> +
> +	kfree(tmp);
> +	return ret;
> +}
> +
> +static ssize_t
> +i3cdev_write(struct file *file, const char __user *buf, size_t count,
> +	     loff_t *f_pos)
> +{
> +	struct i3cdev_data *i3cdev = file->private_data;
> +	struct i3c_device *i3c = i3cdev->i3c;
> +	struct i3c_priv_xfer xfers = {
> +		.rnw = false,
> +		.len = count,
> +	};
> +	char *tmp;
> +	int ret;
> +
> +	tmp = memdup_user(buf, count);
> +	if (IS_ERR(tmp))
> +		return PTR_ERR(tmp);
> +
> +	xfers.data.out = tmp;
> +
> +	dev_dbg(i3cdev->dev, "Writing %zu bytes.\n", count);
> +
> +	ret = i3c_device_do_priv_xfers(i3c, &xfers, 1);
> +	kfree(tmp);
> +
> +	return !ret ? count : ret;
> +}
> +
> +static int
> +i3cdev_ioctl_priv_xfers(struct i3c_device *i3c,
> +			struct i3cdev_priv_xfers __user *uxfers)
> +{
> +	struct i3cdev_priv_xfers xfers;
> +	struct i3cdev_priv_xfer *uxfer_array;
> +	struct i3c_priv_xfer *xfer_array;
> +	unsigned int i;
> +	int ret;
> +
> +	if (copy_from_user(&xfers, uxfers, sizeof(xfers)))
> +		return -EFAULT;
> +
> +	/* TODO: Add a limit for xfers.nxfers. */
> +	uxfer_array = memdup_user(u64_to_user_ptr(xfers.xfers),
> +				  xfers.nxfers * sizeof(*uxfer_array));
> +	if (!uxfer_array)
> +		return -ENOMEM;
> +
> +	xfer_array = kmalloc_array(xfers.nxfers, sizeof(*xfer_array),
> +				   GFP_KERNEL);
> +	if (!xfer_array) {
> +		ret = -ENOMEM;
> +		goto out_free_uxfer_array;
> +	}
> +
> +	/* TODO Add a limit for max in/out size. */
> +	for (i = 0; i < xfers.nxfers; i++) {
> +		void __user *udata = u64_to_user_ptr(uxfer_array[i].data);
> +		void *data;
> +
> +		xfer_array[i].rnw = uxfer_array[i].rnw;
> +		xfer_array[i].len = uxfer_array[i].len;
> +
> +		if (!xfer_array[i].rnw) {
> +			data = memdup_user(udata, xfer_array[i].len);
> +		} else {
> +			data = kzalloc(xfer_array[i].len, GFP_KERNEL);
> +			if (data)
> +				data = ERR_PTR(-ENOMEM);
> +		}
> +
> +		if (IS_ERR(data)) {
> +			ret = PTR_ERR(xfer_array[i].data.in);
> +			goto out_free_xfer_array;
> +		}
> +
> +		xfer_array[i].data.in = data;
> +	}
> +
> +	ret = i3c_device_do_priv_xfers(i3c, xfer_array, xfers.nxfers);
> +
> +	if (!ret) {
> +		for (i = 0; i < xfers.nxfers; i++) {
> +			void __user *udata = u64_to_user_ptr(uxfer_array[i].data);
> +			void *data = xfer_array[i].data.in;
> +
> +			if (!xfer_array[i].rnw)
> +				continue;
> +
> +			if (copy_to_user(udata, data, xfer_array[i].len)) {
> +				ret = -EFAULT;
> +				goto out_free_xfer_array;
> +			}
> +		}
> +	}
> +
> +out_free_xfer_array:
> +	for (i = 0; i < xfers.nxfers; i++)
> +		kfree(xfer_array[i].data.in);
> +
> +	kfree(xfer_array);
> +
> +out_free_uxfer_array:
> +	kfree(uxfer_array);
> +	return ret;
> +}
> +
> +static long
> +i3cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> +	struct i3cdev_data *i3cdev = file->private_data;
> +	void __user *udata = (void __user *)arg;
> +	int ret = -EACCES;
> +
> +	dev_dbg(i3cdev->dev, "ioctl, cmd=0x%02x, arg=0x%02lx\n", cmd, arg);
> +
> +	switch (cmd) {
> +	case I3CDEV_PRIV_XFER:
> +		ret = i3cdev_ioctl_priv_xfers(i3cdev->i3c, udata);
> +		break;
> +	default:
> +		return -ENOTTY;
> +	}
> +
> +	return ret;
> +}
> +
> +static int i3cdev_open(struct inode *inode, struct file *file)
> +{
> +	struct i3cdev_data *i3cdev = container_of(inode->i_cdev,
> +						  struct i3cdev_data,
> +						  cdev);
> +	file->private_data = i3cdev;
> +
> +	return 0;
> +}
> +
> +static int i3cdev_release(struct inode *inode, struct file *file)
> +{
> +	file->private_data = NULL;
> +
> +	return 0;
> +}
> +
> +static const struct file_operations i3cdev_fops = {
> +	.owner = THIS_MODULE,
> +	.read = i3cdev_read,
> +	.write = i3cdev_write,
> +	.unlocked_ioctl	= i3cdev_ioctl,
> +	.compat_ioctl = compat_ptr_ioctl,
> +	.open = i3cdev_open,
> +	.release = i3cdev_release,
> +};
> +
> +/* ------------------------------------------------------------------------- */
> +
> +static struct class *i3cdev_class;
> +
> +static int i3cdev_probe(struct i3c_device *i3c)
> +{
> +	struct device *dev = i3cdev_to_dev(i3c);
> +	struct i3cdev_data *i3cdev;
> +	int ret;
> +	int id;
> +
> +	i3cdev = devm_kzalloc(dev, sizeof(*i3cdev), GFP_KERNEL);
> +	if (!i3cdev)
> +		return -ENOMEM;
> +
> +	ret = ida_simple_get(&i3cdev_ida, 0, MAX_I3CDEV_DEVS, GFP_KERNEL);
> +	if (ret < 0) {
> +		dev_err(dev, "no minor number available!\n");
> +		return ret;
> +	}
> +
> +	i3cdev->i3c = i3c;
> +	i3cdev->devt = MKDEV(MAJOR(i3cdev_first_chrdev),
> +			     MINOR(i3cdev_first_chrdev) + ret);
> +	i3cdev_set_drvdata(i3c, i3cdev);
> +	cdev_init(&i3cdev->cdev, &i3cdev_fops);
> +	i3cdev->cdev.owner = THIS_MODULE;
> +	ret = cdev_add(&i3cdev->cdev, i3cdev->devt, 1);
> +	if (ret)
> +		goto error_free_id;
> +
> +	i3cdev->dev = device_create(i3cdev_class, dev, i3cdev->devt,
> +				    NULL, "i3cdev%d", id);
> +	if (IS_ERR(i3cdev->dev)) {
> +		ret = PTR_ERR(i3cdev->dev);
> +		goto error_free_cdev;
> +	}
> +
> +	return 0;
> +
> +error_free_cdev:
> +	cdev_del(&i3cdev->cdev);
> +error_free_id:
> +	ida_free(&i3cdev_ida,
> +		 MINOR(i3cdev->devt) - MINOR(i3cdev_first_chrdev));
> +	return ret;
> +}
> +
> +static int i3cdev_remove(struct i3c_device *i3c)
> +{
> +	struct i3cdev_data *i3cdev;
> +
> +	i3cdev = i3cdev_get_drvdata(i3c);
> +
> +	device_destroy(i3cdev_class, i3cdev->devt);
> +	cdev_del(&i3cdev->cdev);
> +	ida_simple_remove(&i3cdev_ida,
> +			  MINOR(i3cdev->devt) - MINOR(i3cdev_first_chrdev));
> +
> +	return 0;
> +}
> +
> +static const struct i3c_device_id i3cdev_ids[] = {
> +	{ /* Sentinel */ },
> +};
> +
> +static struct i3c_driver i3cdev_driver = {
> +	.probe = i3cdev_probe,
> +	.remove = i3cdev_remove,
> +	.id_table = i3cdev_ids,
> +};
> +
> +static int __init i3cdev_init(void)
> +{
> +	int ret;
> +
> +	ret = alloc_chrdev_region(&i3cdev_first_chrdev, 0, MAX_I3CDEV_DEVS,
> +				  "i3cdev");
> +	if (ret)
> +		return ret;
> +
> +	i3cdev_class = class_create(THIS_MODULE, "i3cdev");
> +	if (IS_ERR(i3cdev_class))
> +		goto err_unreg_chrdev_region;
> +
> +	ret = i3c_driver_register(&i3cdev_driver);
> +	if (ret)
> +		goto err_destroy_class;
> +
> +	return 0;
> +
> +err_destroy_class:
> +	class_destroy(i3cdev_class);
> +err_unreg_chrdev_region:
> +	unregister_chrdev_region(i3cdev_first_chrdev, MAX_I3CDEV_DEVS);
> +	return ret;
> +}
> +module_init(i3cdev_init);
> +
> +static void __exit i3cdev_exit(void)
> +{
> +	i3c_driver_unregister(&i3cdev_driver);
> +	class_destroy(i3cdev_class);
> +	unregister_chrdev_region(i3cdev_first_chrdev, MAX_I3CDEV_DEVS);
> +}
> +module_exit(i3cdev_exit);
> +
> +MODULE_AUTHOR("Vitor Soares <soares@...opsys.com>");
> +MODULE_DESCRIPTION("I3C /dev entries driver");
> +MODULE_LICENSE("GPL");
> diff --git a/include/uapi/linux/i3c/i3cdev.h b/include/uapi/linux/i3c/i3cdev.h
> new file mode 100644
> index 000000000000..305dc029ca2d
> --- /dev/null
> +++ b/include/uapi/linux/i3c/i3cdev.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * Copyright (c) 2020 Synopsys, Inc. and/or its affiliates.
> + *
> + * Author: Vitor Soares <vitor.soares@...opsys.com>
> + */
> +
> +#ifndef _UAPI_I3C_DEV_H_
> +#define _UAPI_I3C_DEV_H_
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +/* IOCTL commands */
> +#define I3C_DEV_IOC_MAGIC	0x07
> +
> +/**
> + * struct i3c_ioc_priv_xfer - I3C SDR ioctl private transfer
> + * @data: Holds pointer to userspace buffer with transmit data.
> + * @len: Length of data buffer buffers, in bytes.
> + * @rnw: encodes the transfer direction. true for a read, false for a write
> + */
> +struct i3cdev_priv_xfer {
> +	__u64 data;
> +	__u16 len;
> +	__u8 rnw;
> +	__u8 pad[5];
> +};
> +
> +struct i3cdev_priv_xfers {
> +	__u64 nxfers;
> +	__u64 xfers;
> +};
> +
> +#define I3CDEV_PRIV_XFER \
> +	_IOWR(I3C_DEV_IOC_MAGIC, 0, struct i3cdev_priv_xfers)
> +
> +#endif

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