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Date: Wed, 01 Apr 2020 16:53:25 -0700
From: rishabhb@...eaurora.org
To: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org,
psodagud@...eaurora.org, tsoni@...eaurora.org,
sidgup@...eaurora.org
Subject: Re: [PATCH v2 1/2] remoteproc: Add character device interface
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@...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);
>
> 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
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