Date:   Mon, 6 Apr 2020 11:01:03 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...com>
To:     <rishabhb@...eaurora.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-remoteproc@...r.kernel.org>,
        <bjorn.andersson@...aro.org>, <psodagud@...eaurora.org>,
        <tsoni@...eaurora.org>, <sidgup@...eaurora.org>
Subject: Re: [PATCH v2 1/2] remoteproc: Add character device interface



On 4/3/20 9:13 PM, rishabhb@...eaurora.org wrote:
> On 2020-04-02 10:28, Arnaud POULIQUEN wrote:
>> Hi
>>
>> On 4/1/20 2:03 AM, 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.
>>
>> Sorry I'm late in the discussion, I hope I've gone through the whole
>> discussion so I don't reopen a closed point...
>>
>> Something here is not crystal clear to me so I'd rather share it...
>>
>> I suppose that you the automatic restart of the application is not possible to
>> stop and restart the remote processor...
> Yes correct, while we wait for the application to restart we might observe a
> fatal crash.
>>
>> Why this use case can not be solved by a process monitor or a service
>> in userland that detects the application crash and stop the remote
>> firmware using
>> the sysfs interface?
>>
> What happens in the case where the process monitor itself crashes? This is
> actually the approach we follow in our downstream code. We have a central entity
> in userspace that controls bootup/shutdown of some remote processors based on the
> votes from userspace clients. We have observed cases where this entity
> itself crashes and remote processors are left hanging.

Your description makes me feel like this patch is only a workaround of something that
should be fixed in the userland, even if i understand that hanging is one of the most
critical problem and have to be fixed.
For instance, how to handle several applications that interact with the remote processor
( e.g. rpmsg service applications) how to stop and restart everything. Using the char
device would probaly resolve only a part of the issue...

I'm not aware about your environment and i'm not a userland expert. But what i still not
understand why a parent process can not do the job...
I just test a simple script on my side that treat the kill -9 of an application
("cat" in my case).

#start the remote firmware
cp  $1 /lib/firmware/
echo $1> /sys/class/remoteproc/remoteproc0/firmware
echo start >/sys/class/remoteproc/remoteproc0/state
#your binary
cat /dev/kmsg
# stop the remote firmware in case of crash (and potentially some other apps)
echo stop >/sys/class/remoteproc/remoteproc0/state

Anyway, it's just my feeling, let other people give their feedback.

>> I just want to be sure that there is no alternative to this, because
>> having two ways
>> for application to shutdown the firmware seems to me confusing...
> Does making this interface optional/configurable helps?
>>
>> What about the opposite service, mean inform the application that the remote
>> processor is crashed?
>> Do you identify such need? or the "auto" crash recovery is sufficient?
> Auto recovery works perfectly for us. Although there is a mechanism in
> place using QMI(Qualcomm MSM interface) that can notify clients about remote
> processor crash.

Thanks for the information.

Regards
Arnaud

>>
>> Thanks,
>> Arnaud
>>>
>>> Signed-off-by: Rishabh Bhatnagar <rishabhb@...eaurora.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);
>>> +
>>> +    if (!rproc)
>>> +        return -EINVAL;
>>> +
>>> +    if (rproc->state == RPROC_RUNNING)
>>> +        return -EBUSY;
>>> +
>>> +    return rproc_boot(rproc);
>>> +}
>>> +
>>> +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_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,
>>> +                   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");
>>> +    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;
>>> +    }
>>> +}
>>> +
>>> +void __exit rproc_exit_cdev(void)
>>> +{
>>> +    __unregister_chrdev(MAJOR(rproc_cdev), 0, NUM_RPROC_DEVICES, "rproc");
>>> +}
>>> 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;
>>>  };
>>>
>>>  /**
>>>

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