Re: [RFC PATCH] Change coresight tmc from misc device to cdev device

Mathieu Poirier
2021-12-09T18:08:53Z

Hi Jay,

On Wed, Dec 01, 2021 at 03:09:42PM +0800, Jay Chen wrote:
> For coresight in the server scenario, if there are too many
> cpu cores and too many tmc peripherals, the error of insufficient
> device numbers will occur by misc device
>

There really is more than 128 miscdevice allocated in your system? How may TMC
do you have?

> Signed-off-by: Jay Chen <jkchen@linux.alibaba.com>
> ---
> drivers/hwtracing/coresight/coresight-core.c | 53 +++++++++++++++++++
> .../hwtracing/coresight/coresight-tmc-core.c | 13 ++---
> drivers/hwtracing/coresight/coresight-tmc.h | 4 +-
> include/linux/coresight.h | 23 ++++++++
> 4 files changed, 83 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 8a18c71df37a..b0cca3060f4e 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -17,6 +17,7 @@
> #include <linux/coresight.h>
> #include <linux/of_platform.h>
> #include <linux/delay.h>
> +#include <linux/cdev.h>
> #include <linux/pm_runtime.h>
>
> #include "coresight-etm-perf.h"
> @@ -1567,6 +1568,58 @@ void coresight_release_platform_data(struct coresight_device *csdev,
> coresight_remove_conns_sysfs_group(csdev);
> }
>
> +int coresight_cdev_register(struct coresight_cdev *cdev, const struct file_operations *fops,
> + const char *name)
> +{
> + struct device *device;
> +
> + if (alloc_chrdev_region(&cdev->devno, 0, 1, name)) {
> + pr_err("failed to create the coresight cdev region\n");
> + return -EFAULT;
> + }
> +
> + cdev->class = class_create(THIS_MODULE, name);
> + if (IS_ERR(cdev->class)) {
> + pr_err("failed to create the coresight class\n");
> + goto coresight_unregister_region;
> + }

From the above a new class is created for every TMC, even if they are all the
same. A better way to do this would be to create a single TMC class with a new
cdev for every new TMC.

To do this alloc_chrdev_region() and class_create() have to be called when the
module is added to the system. Have a look at funnel_init() on how to refactor
the TMC core driver with an init function and rpmsg_chrdev_init() for the chrdev
region allocation and the class creation.

From there every time a TMC is probe cdev_init() and cdev_add() can be called -
look at rpmsg_chrdev_probe() for an example. Instead of using an IDA to pick out
a minor number you should be able to use dev_list->nr_idx - 1.

Thanks,
Mathieu

> +
> + cdev_init(&cdev->cdev, fops);
> + if (cdev_add(&cdev->cdev, cdev->devno, 1)) {
> + pr_err("failed to add the coresight cdev\n");
> + goto coresight_free_class;
> + }
> +
> + device = device_create(cdev->class, NULL, cdev->devno,
> + cdev, name);
> + if (IS_ERR(device)) {
> + pr_err("failed to create device for coresight\n");
> + goto coresight_del_cdev;
> + }
> +
> + return 0;
> +
> +coresight_del_cdev:
> + cdev_del(&cdev->cdev);
> +coresight_free_class:
> + class_destroy(cdev->class);
> +coresight_unregister_region:
> + unregister_chrdev_region(cdev->devno, 1);
> +
> + return -EFAULT;
> +}
> +EXPORT_SYMBOL_GPL(coresight_cdev_register);
> +
> +int coresight_cdev_unregister(struct coresight_cdev *cdev)
> +{
> + device_destroy(cdev->class, cdev->devno);
> + cdev_del(&cdev->cdev);
> + class_destroy(cdev->class);
> + unregister_chrdev_region(cdev->devno, 1);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(coresight_cdev_unregister);
> +
> struct coresight_device *coresight_register(struct coresight_desc *desc)
> {
> int ret;
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
> index 74c6323d4d6a..c4aae8ff65eb 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-core.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
> @@ -147,7 +147,7 @@ static int tmc_open(struct inode *inode, struct file *file)
> {
> int ret;
> struct tmc_drvdata *drvdata = container_of(file->private_data,
> - struct tmc_drvdata, miscdev);
> + struct tmc_drvdata, cdev);
>
> ret = tmc_read_prepare(drvdata);
> if (ret)
> @@ -179,7 +179,7 @@ static ssize_t tmc_read(struct file *file, char __user *data, size_t len,
> char *bufp;
> ssize_t actual;
> struct tmc_drvdata *drvdata = container_of(file->private_data,
> - struct tmc_drvdata, miscdev);
> + struct tmc_drvdata, cdev);
> actual = tmc_get_sysfs_trace(drvdata, *ppos, len, &bufp);
> if (actual <= 0)
> return 0;
> @@ -200,7 +200,7 @@ static int tmc_release(struct inode *inode, struct file *file)
> {
> int ret;
> struct tmc_drvdata *drvdata = container_of(file->private_data,
> - struct tmc_drvdata, miscdev);
> + struct tmc_drvdata, cdev);
>
> ret = tmc_read_unprepare(drvdata);
> if (ret)
> @@ -529,10 +529,7 @@ static int tmc_probe(struct amba_device *adev, const struct amba_id *id)
> goto out;
> }
>
> - drvdata->miscdev.name = desc.name;
> - drvdata->miscdev.minor = MISC_DYNAMIC_MINOR;
> - drvdata->miscdev.fops = &tmc_fops;
> - ret = misc_register(&drvdata->miscdev);
> + ret = coresight_cdev_register(&drvdata->cdev, &tmc_fops, desc.name);
> if (ret)
> coresight_unregister(drvdata->csdev);
> else
> @@ -572,7 +569,7 @@ static void tmc_remove(struct amba_device *adev)
> * etb fops in this case, device is there until last file
> * handler to this device is closed.
> */
> - misc_deregister(&drvdata->miscdev);
> + coresight_cdev_unregister(&drvdata->cdev);
> coresight_unregister(drvdata->csdev);
> }
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
> index b91ec7dde7bc..c37e2ed1cb9d 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc.h
> +++ b/drivers/hwtracing/coresight/coresight-tmc.h
> @@ -166,7 +166,7 @@ struct etr_buf {
> * struct tmc_drvdata - specifics associated to an TMC component
> * @base: memory mapped base address for this component.
> * @csdev: component vitals needed by the framework.
> - * @miscdev: specifics to handle "/dev/xyz.tmc" entry.
> + * @cdev: specifics to handle "/dev/xyz.tmc" entry.
> * @spinlock: only one at a time pls.
> * @pid: Process ID of the process being monitored by the session
> * that is using this component.
> @@ -188,7 +188,7 @@ struct etr_buf {
> struct tmc_drvdata {
> void __iomem *base;
> struct coresight_device *csdev;
> - struct miscdevice miscdev;
> + struct coresight_cdev cdev;
> spinlock_t spinlock;
> pid_t pid;
> bool reading;
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index 93a2922b7653..aebe8b8327ad 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -9,6 +9,7 @@
> #include <linux/device.h>
> #include <linux/io.h>
> #include <linux/perf_event.h>
> +#include <linux/cdev.h>
> #include <linux/sched.h>
>
> /* Peripheral id registers (0xFD0-0xFEC) */
> @@ -252,6 +253,12 @@ struct coresight_device {
> void *active_cscfg_ctxt;
> };
>
> +struct coresight_cdev {
> + dev_t devno;
> + struct class *class;
> + struct cdev cdev;
> +};
> +
> /*
> * coresight_dev_list - Mapping for devices to "name" index for device
> * names.
> @@ -506,6 +513,10 @@ void coresight_relaxed_write64(struct coresight_device *csdev,
> u64 val, u32 offset);
> void coresight_write64(struct coresight_device *csdev, u64 val, u32 offset);
>
> +int coresight_cdev_register(struct coresight_cdev *cdev, const struct file_operations *fops,
> + const char *name);
> +
> +int coresight_cdev_unregister(struct coresight_cdev *cdev);
> #else
> static inline struct coresight_device *
> coresight_register(struct coresight_desc *desc) { return NULL; }
> @@ -581,6 +592,18 @@ static inline void coresight_write64(struct coresight_device *csdev, u64 val, u3
> {
> }
>
> +static inline int coresight_cdev_register(struct coresight_cdev *cdev,
> + const struct file_operations *fops,
> + const char *name)
> +{
> + return 0;
> +}
> +
> +static inline int coresight_cdev_unregister(struct coresight_cdev *cdev)
> +{
> + return 0;
> +}
> +
> #endif /* IS_ENABLED(CONFIG_CORESIGHT) */
>
> extern int coresight_get_cpu(struct device *dev);
> --
> 2.27.0
>