Re: [PATCH 1/2] remoteproc: Add userspace char device driver

["Clément Leger" <cleger@kalrayinc.com>]

Hi Rishabh,

While being interesting to have a such a userspace interface, I have
some remarks.

----- On 26 Mar, 2020, at 17:50, Rishabh Bhatnagar rishabhb@codeaurora.org wrote:

> Add the driver for creating the character device interface for
> userspace applications. The character device interface can be used
> in order to boot up and shutdown the remote processor.
> This might be helpful for remote processors that are booted by
> userspace applications and need to shutdown when the application
> crahes/shutsdown.
> 
> Change-Id: If23c8986272bb7c943eb76665f127ff706f12394
> Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
> ---
> drivers/remoteproc/Makefile               |  1 +
> drivers/remoteproc/remoteproc_internal.h  |  6 +++
> drivers/remoteproc/remoteproc_userspace.c | 90 +++++++++++++++++++++++++++++++
> include/linux/remoteproc.h                |  2 +
> 4 files changed, 99 insertions(+)
> create mode 100644 drivers/remoteproc/remoteproc_userspace.c
> 
> diff --git a/drivers/remoteproc/Makefile b/drivers/remoteproc/Makefile
> index e30a1b1..facb3fa 100644
> --- a/drivers/remoteproc/Makefile
> +++ b/drivers/remoteproc/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_REMOTEPROC)		+= remoteproc.o
> remoteproc-y				:= remoteproc_core.o
> remoteproc-y				+= remoteproc_debugfs.o
> remoteproc-y				+= remoteproc_sysfs.o
> +remoteproc-y				+= remoteproc_userspace.o
> remoteproc-y				+= remoteproc_virtio.o
> remoteproc-y				+= remoteproc_elf_loader.o
> obj-$(CONFIG_IMX_REMOTEPROC)		+= imx_rproc.o
> diff --git a/drivers/remoteproc/remoteproc_internal.h
> b/drivers/remoteproc/remoteproc_internal.h
> index 493ef92..97513ba 100644
> --- a/drivers/remoteproc/remoteproc_internal.h
> +++ b/drivers/remoteproc/remoteproc_internal.h
> @@ -47,6 +47,9 @@ struct dentry *rproc_create_trace_file(const char *name,
> struct rproc *rproc,
> int rproc_init_sysfs(void);
> void rproc_exit_sysfs(void);
> 
> +void rproc_init_cdev(void);
> +void rproc_exit_cdev(void);
> +
> void rproc_free_vring(struct rproc_vring *rvring);
> int rproc_alloc_vring(struct rproc_vdev *rvdev, int i);
> 
> @@ -63,6 +66,9 @@ struct resource_table *rproc_elf_find_loaded_rsc_table(struct
> rproc *rproc,
> struct rproc_mem_entry *
> rproc_find_carveout_by_name(struct rproc *rproc, const char *name, ...);
> 
> +/* from remoteproc_userspace.c */
> +int rproc_char_device_add(struct rproc *rproc);
> +
> static inline
> int rproc_fw_sanity_check(struct rproc *rproc, const struct firmware *fw)
> {
> diff --git a/drivers/remoteproc/remoteproc_userspace.c
> b/drivers/remoteproc/remoteproc_userspace.c
> new file mode 100644
> index 0000000..2ef7679
> --- /dev/null
> +++ b/drivers/remoteproc/remoteproc_userspace.c
> @@ -0,0 +1,90 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Character device interface driver for Remoteproc framework.
> + *
> + * Copyright (c) 2020, The Linux Foundation. All rights reserved.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/fs.h>
> +#include <linux/cdev.h>
> +#include <linux/mutex.h>
> +#include <linux/remoteproc.h>
> +
> +#include "remoteproc_internal.h"
> +
> +#define NUM_RPROC_DEVICES	64
> +static dev_t rproc_cdev;
> +static DEFINE_IDA(cdev_minor_ida);
> +
> +static int rproc_open(struct inode *inode, struct file *file)
> +{
> +	struct rproc *rproc;
> +
> +	rproc = container_of(inode->i_cdev, struct rproc, char_dev);
> +	if (!rproc)
> +		return -EINVAL;
> +
> +	return rproc_boot(rproc);
> +}

What happens if multiple user open this chardev ? Apparently,
rproc_boot returns 0 if already powered_up, so the next user won't know
what is the state of the rproc.
Exclusive access could probably be a good idea.

> +
> +static int rproc_release(struct inode *inode, struct file *file)
> +{
> +	struct rproc *rproc;
> +
> +	rproc = container_of(inode->i_cdev, struct rproc, char_dev);
> +	if (!rproc)
> +		return -EINVAL;
> +
> +	rproc_shutdown(rproc);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations rproc_fops = {
> +	.open = rproc_open,
> +	.release = rproc_release,
> +};
> +
> +int rproc_char_device_add(struct rproc *rproc)
> +{
> +	int ret, minor;
> +	dev_t cdevt;
> +
> +	minor = ida_simple_get(&cdev_minor_ida, 0, NUM_RPROC_DEVICES,
> +			GFP_KERNEL);
> +	if (minor < 0) {
> +	pr_err("%s: No more minor numbers left! rc:%d\n", __func__,
> +							minor);
> +		return -ENODEV;
> +	}

How can you make the link between the chardev and the device instance ?
In our case, we have several remoteproc instances and thus we will end
up having multiple chardev.

Regards,

Clément

> +
> +	cdev_init(&rproc->char_dev, &rproc_fops);
> +	rproc->char_dev.owner = THIS_MODULE;
> +
> +	cdevt = MKDEV(MAJOR(rproc_cdev), minor);
> +	ret = cdev_add(&rproc->char_dev, cdevt, 1);
> +	if (ret < 0)
> +		ida_simple_remove(&cdev_minor_ida, minor);
> +
> +	rproc->dev.devt = cdevt;
> +
> +	return ret;
> +}
> +
> +void __init rproc_init_cdev(void)
> +{
> +	int ret;
> +
> +	ret = alloc_chrdev_region(&rproc_cdev, 0, NUM_RPROC_DEVICES, "rproc");
> +	if (ret < 0) {
> +		pr_err("Failed to alloc rproc_cdev region, err %d\n", ret);
> +		return;
> +	}
> +}
> +
> +void __exit rproc_exit_cdev(void)
> +{
> +	unregister_chrdev_region(MKDEV(MAJOR(rproc_cdev), 0),
> +				NUM_RPROC_DEVICES);
> +}
> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> index 16ad666..c4ca796 100644
> --- a/include/linux/remoteproc.h
> +++ b/include/linux/remoteproc.h
> @@ -37,6 +37,7 @@
> 
> #include <linux/types.h>
> #include <linux/mutex.h>
> +#include <linux/cdev.h>
> #include <linux/virtio.h>
> #include <linux/completion.h>
> #include <linux/idr.h>
> @@ -514,6 +515,7 @@ struct rproc {
> 	bool auto_boot;
> 	struct list_head dump_segments;
> 	int nb_vdev;
> +	struct cdev char_dev;
> };
> 
> /**
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project