Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit
Date:   Wed, 01 Apr 2020 16:53:25 -0700
From:   rishabhb@codeaurora.org
To:     Bjorn Andersson <bjorn.andersson@linaro.org>
Cc:     linux-kernel@vger.kernel.org, linux-remoteproc@vger.kernel.org,
        psodagud@codeaurora.org, tsoni@codeaurora.org,
        sidgup@codeaurora.org
Subject: Re: [PATCH v2 1/2] remoteproc: Add character device interface
In-Reply-To: <20200401200827.GF267644@minitux>
References: <1585699438-14394-1-git-send-email-rishabhb@codeaurora.org>
 <20200401200827.GF267644@minitux>
Message-ID: <27cae9aae50385f9123cb0987edeec1c@codeaurora.org>
User-Agent: Roundcube Webmail/1.3.9
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2020-04-01 13:08, Bjorn Andersson wrote:
> On Tue 31 Mar 17:03 PDT 2020, Rishabh Bhatnagar wrote:
> 
>> Add the character device interface for userspace applications.
>> This interface can be used in order to boot up and shutdown
>> remote subsystems. Currently there is only a sysfs interface
>> which the userspace clients can use. If a usersapce application
>> crashes after booting the remote processor does not get any
>> indication about the crash. It might still assume that the
>> application is running. For example modem uses remotefs service
>> to fetch data from disk/flash memory. If the remotefs service
>> crashes, modem keeps on requesting data which might lead to a
>> crash. Adding a character device interface makes the remote
>> processor tightly coupled with the user space application.
>> A crash of the application leads to a close on the file descriptors
>> therefore shutting down the remoteproc.
>> 
>> Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
>> ---
>>  drivers/remoteproc/Kconfig               |   9 +++
>>  drivers/remoteproc/Makefile              |   1 +
>>  drivers/remoteproc/remoteproc_cdev.c     | 100 
>> +++++++++++++++++++++++++++++++
>>  drivers/remoteproc/remoteproc_internal.h |  22 +++++++
>>  include/linux/remoteproc.h               |   2 +
>>  5 files changed, 134 insertions(+)
>>  create mode 100644 drivers/remoteproc/remoteproc_cdev.c
>> 
>> diff --git a/drivers/remoteproc/Kconfig b/drivers/remoteproc/Kconfig
>> index de3862c..6374b79 100644
>> --- a/drivers/remoteproc/Kconfig
>> +++ b/drivers/remoteproc/Kconfig
>> @@ -14,6 +14,15 @@ config REMOTEPROC
>> 
>>  if REMOTEPROC
>> 
>> +config REMOTEPROC_CDEV
>> +	bool "Remoteproc character device interface"
>> +	help
>> +	  Say y here to have a character device interface for Remoteproc
>> +	  framework. Userspace can boot/shutdown remote processors through
>> +	  this interface.
>> +
>> +	  It's safe to say N if you don't want to use this interface.
>> +
>>  config IMX_REMOTEPROC
>>  	tristate "IMX6/7 remoteproc support"
>>  	depends on ARCH_MXC
>> diff --git a/drivers/remoteproc/Makefile b/drivers/remoteproc/Makefile
>> index e30a1b1..b7d4f77 100644
>> --- a/drivers/remoteproc/Makefile
>> +++ b/drivers/remoteproc/Makefile
>> @@ -9,6 +9,7 @@ remoteproc-y				+= remoteproc_debugfs.o
>>  remoteproc-y				+= remoteproc_sysfs.o
>>  remoteproc-y				+= remoteproc_virtio.o
>>  remoteproc-y				+= remoteproc_elf_loader.o
>> +obj-$(CONFIG_REMOTEPROC_CDEV)		+= remoteproc_cdev.o
>>  obj-$(CONFIG_IMX_REMOTEPROC)		+= imx_rproc.o
>>  obj-$(CONFIG_MTK_SCP)			+= mtk_scp.o mtk_scp_ipi.o
>>  obj-$(CONFIG_OMAP_REMOTEPROC)		+= omap_remoteproc.o
>> diff --git a/drivers/remoteproc/remoteproc_cdev.c 
>> b/drivers/remoteproc/remoteproc_cdev.c
>> new file mode 100644
>> index 0000000..8182bd1
>> --- /dev/null
>> +++ b/drivers/remoteproc/remoteproc_cdev.c
>> @@ -0,0 +1,100 @@
>> +// 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/cdev.h>
>> +#include <linux/fs.h>
>> +#include <linux/module.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_cdev_open(struct inode *inode, struct file *file)
>> +{
>> +	struct rproc *rproc;
>> +
>> +	rproc = container_of(inode->i_cdev, struct rproc, char_dev);
> 
> I would prefer this to be a on a single line
> 	struct rproc *rproc = container_of(..);
> 
>> +
>> +	if (!rproc)
> 
> I don't think this is possible.
> 
>> +		return -EINVAL;
>> +
>> +	if (rproc->state == RPROC_RUNNING)
>> +		return -EBUSY;
>> +
> 
> This is racy, it's possible that state wasn't RUNNING, but at the time
> we're entering rproc_boot() it is - or as Clement correctly points out,
> the core might be in CRASHED state.
> 
I can check for OFFLINE state and only then call rproc_boot.
But we would need to check inside rproc_boot if the state was OFFLINE as 
well.
Same issue we might need to fix for sysfs interface?
>> +	return rproc_boot(rproc);
> 
> Feels like we would want a variant of rproc_boot() that doesn't do
> refcounting... Maybe a rproc_boot_exclusive() that takes the mutex and
> then fails if the core is refcounted already?
> 
>> +}
>> +
>> +static int rproc_cdev_release(struct inode *inode, struct file *file)
>> +{
>> +	struct rproc *rproc;
>> +
>> +	rproc = container_of(inode->i_cdev, struct rproc, char_dev);
>> +
>> +	if (!rproc || rproc->state != RPROC_RUNNING)
>> +		return -EINVAL;
> 
> rproc can't be NULL here and the core might be in CRASHED state here, 
> in
> which case we still want to abort that and shut down the core...
> 
> Note that in the event of calling close() the return value is discarded
> on the way to userspace and in the event that the process is killed we
> still expect the remoteproc to be shut down (if the refcount hit 0).
> 
>> +
>> +	rproc_shutdown(rproc);
>> +
>> +	return 0;
>> +}
>> +
>> +static const struct file_operations rproc_fops = {
>> +	.open = rproc_cdev_open,
>> +	.release = rproc_cdev_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,
> 
> Can't you use rproc->index as minor?
> 
>> +			       GFP_KERNEL);
>> +	if (minor < 0) {
>> +		dev_err(&rproc->dev, "%s: No more minor numbers left! rc:%d\n",
>> +			__func__, minor);
>> +		return -ENODEV;
>> +	}
>> +
>> +	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 rproc_char_device_remove(struct rproc *rproc)
>> +{
>> +	__unregister_chrdev(MAJOR(rproc->dev.devt), MINOR(rproc->dev.devt), 
>> 1,
>> +			    "rproc");
> 
> Shouldn't this be cdev_del()?
_unregist_chrdev should delete the cdev internally.
> 
>> +	ida_simple_remove(&cdev_minor_ida, MINOR(rproc->dev.devt));
>> +}
>> +
>> +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;
> 
> Drop this return, and hence the {}
> 
>> +	}
>> +}
>> +
>> +void __exit rproc_exit_cdev(void)
>> +{
>> +	__unregister_chrdev(MAJOR(rproc_cdev), 0, NUM_RPROC_DEVICES, 
>> "rproc");
> 
> unregister_chrdev_region();
> 
we might want to delete character devices as well, which is done by 
__unregister_chrdev
>> +}
>> diff --git a/drivers/remoteproc/remoteproc_internal.h 
>> b/drivers/remoteproc/remoteproc_internal.h
>> index 493ef92..28d61a1 100644
>> --- a/drivers/remoteproc/remoteproc_internal.h
>> +++ b/drivers/remoteproc/remoteproc_internal.h
>> @@ -47,6 +47,27 @@ struct dentry *rproc_create_trace_file(const char 
>> *name, struct rproc *rproc,
>>  int rproc_init_sysfs(void);
>>  void rproc_exit_sysfs(void);
>> 
>> +#ifdef CONFIG_REMOTEPROC_CDEV
>> +void rproc_init_cdev(void);
>> +void rproc_exit_cdev(void);
>> +int rproc_char_device_add(struct rproc *rproc);
>> +void rproc_char_device_remove(struct rproc *rproc);
>> +#else
>> +static inline void rproc_init_cdev(void)
>> +{
>> +}
>> +static inline void rproc_exit_cdev(void)
>> +{
>> +}
>> +static inline int rproc_char_device_add(struct rproc *rproc)
>> +{
>> +	return 0;
>> +}
>> +static inline void  rproc_char_device_remove(struct rproc *rproc)
>> +{
>> +}
>> +#endif
>> +
>>  void rproc_free_vring(struct rproc_vring *rvring);
>>  int rproc_alloc_vring(struct rproc_vdev *rvdev, int i);
>> 
>> @@ -63,6 +84,7 @@ 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, 
>> ...);
>> 
>> +
>>  static inline
>>  int rproc_fw_sanity_check(struct rproc *rproc, const struct firmware 
>> *fw)
>>  {
>> 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