Re: [PATCH v3 16/27] powerpc/powernv/pmem: Register a character device for userspace to interact with

[Andrew Donnellan <ajd@linux.ibm.com>]

On 21/2/20 2:27 pm, Alastair D'Silva wrote:
> From: Alastair D'Silva <alastair@d-silva.org>
> 
> This patch introduces a character device (/dev/ocxl-scmX) which further
> patches will use to interact with userspace.

As with the comments on other patches in this series, this commit 
message is lacking in explanation. What's the purpose of this device?

> 
> Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
> ---
>   arch/powerpc/platforms/powernv/pmem/ocxl.c    | 116 +++++++++++++++++-
>   .../platforms/powernv/pmem/ocxl_internal.h    |   2 +
>   2 files changed, 116 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/pmem/ocxl.c b/arch/powerpc/platforms/powernv/pmem/ocxl.c
> index b8bd7e703b19..63109a870d2c 100644
> --- a/arch/powerpc/platforms/powernv/pmem/ocxl.c
> +++ b/arch/powerpc/platforms/powernv/pmem/ocxl.c
> @@ -10,6 +10,7 @@
>   #include <misc/ocxl.h>
>   #include <linux/delay.h>
>   #include <linux/ndctl.h>
> +#include <linux/fs.h>
>   #include <linux/mm_types.h>
>   #include <linux/memory_hotplug.h>
>   #include "ocxl_internal.h"
> @@ -339,6 +340,9 @@ static void free_ocxlpmem(struct ocxlpmem *ocxlpmem)
>   
>   	free_minor(ocxlpmem);
>   
> +	if (ocxlpmem->cdev.owner)
> +		cdev_del(&ocxlpmem->cdev);
> +
>   	if (ocxlpmem->metadata_addr)
>   		devm_memunmap(&ocxlpmem->dev, ocxlpmem->metadata_addr);
>   
> @@ -396,6 +400,70 @@ static int ocxlpmem_register(struct ocxlpmem *ocxlpmem)
>   	return device_register(&ocxlpmem->dev);
>   }
>   
> +static void ocxlpmem_put(struct ocxlpmem *ocxlpmem)
> +{
> +	put_device(&ocxlpmem->dev);
> +}
> +
> +static struct ocxlpmem *ocxlpmem_get(struct ocxlpmem *ocxlpmem)
> +{
> +	return (get_device(&ocxlpmem->dev) == NULL) ? NULL : ocxlpmem;
> +}
> +
> +static struct ocxlpmem *find_and_get_ocxlpmem(dev_t devno)
> +{
> +	struct ocxlpmem *ocxlpmem;
> +	int minor = MINOR(devno);
> +	/*
> +	 * We don't declare an RCU critical section here, as our AFU
> +	 * is protected by a re0ference counter on the device. By the time the
> +	 * minor number of a device is removed from the idr, the ref count of
> +	 * the device is already at 0, so no user API will access that AFU and
> +	 * this function can't return it.
> +	 */
> +	ocxlpmem = idr_find(&minors_idr, minor);
> +	if (ocxlpmem)
> +		ocxlpmem_get(ocxlpmem);
> +	return ocxlpmem;
> +}
> +
> +static int file_open(struct inode *inode, struct file *file)
> +{
> +	struct ocxlpmem *ocxlpmem;
> +
> +	ocxlpmem = find_and_get_ocxlpmem(inode->i_rdev);
> +	if (!ocxlpmem)
> +		return -ENODEV;
> +
> +	file->private_data = ocxlpmem;
> +	return 0;
> +}
> +
> +static int file_release(struct inode *inode, struct file *file)
> +{
> +	struct ocxlpmem *ocxlpmem = file->private_data;
> +
> +	ocxlpmem_put(ocxlpmem);
> +	return 0;
> +}
> +
> +static const struct file_operations fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= file_open,
> +	.release	= file_release,
> +};
> +
> +/**
> + * create_cdev() - Create the chardev in /dev for the device
> + * @ocxlpmem: the SCM metadata
> + * Return: 0 on success, negative on failure
> + */
> +static int create_cdev(struct ocxlpmem *ocxlpmem)
> +{
> +	cdev_init(&ocxlpmem->cdev, &fops);
> +	return cdev_add(&ocxlpmem->cdev, ocxlpmem->dev.devt, 1);
> +}
> +
>   /**
>    * ocxlpmem_remove() - Free an OpenCAPI persistent memory device
>    * @pdev: the PCI device information struct
> @@ -572,6 +640,11 @@ static int probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>   		goto err;
>   	}
>   
> +	if (create_cdev(ocxlpmem)) {
> +		dev_err(&pdev->dev, "Could not create character device\n");
> +		goto err;
> +	}
> +
>   	elapsed = 0;
>   	timeout = ocxlpmem->readiness_timeout + ocxlpmem->memory_available_timeout;
>   	while (!is_usable(ocxlpmem, false)) {
> @@ -613,20 +686,59 @@ static struct pci_driver pci_driver = {
>   	.shutdown = ocxlpmem_remove,
>   };
>   
> +static int file_init(void)
> +{
> +	int rc;
> +
> +	mutex_init(&minors_idr_lock);
> +	idr_init(&minors_idr);
> +
> +	rc = alloc_chrdev_region(&ocxlpmem_dev, 0, NUM_MINORS, "ocxl-pmem");

If the driver is going to be called "ocxlpmem" can we standardise on 
that without the extra hyphen?

> +	if (rc) {
> +		idr_destroy(&minors_idr);
> +		pr_err("Unable to allocate OpenCAPI persistent memory major number: %d\n", rc);
> +		return rc;
> +	}
> +
> +	ocxlpmem_class = class_create(THIS_MODULE, "ocxl-pmem");
> +	if (IS_ERR(ocxlpmem_class)) {
> +		idr_destroy(&minors_idr);
> +		pr_err("Unable to create ocxl-pmem class\n");
> +		unregister_chrdev_region(ocxlpmem_dev, NUM_MINORS);
> +		return PTR_ERR(ocxlpmem_class);
> +	}
> +
> +	return 0;
> +}
> +
> +static void file_exit(void)
> +{
> +	class_destroy(ocxlpmem_class);
> +	unregister_chrdev_region(ocxlpmem_dev, NUM_MINORS);
> +	idr_destroy(&minors_idr);
> +}
> +
>   static int __init ocxlpmem_init(void)
>   {
> -	int rc = 0;
> +	int rc;
>   
> -	rc = pci_register_driver(&pci_driver);
> +	rc = file_init();
>   	if (rc)
>   		return rc;
>   
> +	rc = pci_register_driver(&pci_driver);
> +	if (rc) {
> +		file_exit();
> +		return rc;
> +	}
> +
>   	return 0;
>   }
>   
>   static void ocxlpmem_exit(void)
>   {
>   	pci_unregister_driver(&pci_driver);
> +	file_exit();
>   }
>   
>   module_init(ocxlpmem_init);
-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd@linux.ibm.com             IBM Australia Limited