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Date:   Fri, 27 Mar 2020 17:09:41 -0700
From:   rishabhb@codeaurora.org
To:     =?UTF-8?Q?Cl=C3=A9ment_Leger?= <cleger@kalrayinc.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        linux-remoteproc <linux-remoteproc@vger.kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Ohad Ben-Cohen <ohad@wizery.com>, psodagud@codeaurora.org,
        tsoni@codeaurora.org, sidgup@codeaurora.org
Subject: Re: [PATCH 1/2] remoteproc: Add userspace char device driver
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On 2020-03-26 10:37, Clément Leger wrote:
> 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.
Since it is synchronized inside rproc_boot multiple users simultaneously
calling open shouldn't be a problem. If it is one after the other then
second caller will get result as 0 and assume that rproc booted 
successfully.
That is the expected flow right?
> 
>> +
>> +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 ?
I do this rproc->dev.devt = cdevt. Let me know of there is a better way
to do this?
> In our case, we have several remoteproc instances and thus we will end
> up having multiple chardev.
> 
> Regards,
> 
> Clément
> 
rproc_char_device_add will be called for each remoteproc that is
added. So we will have one char dev per remoteproc.
>> +
>> +	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