[PATCH v8 17/22] counter: Add character device interface

[William Breathitt Gray]

On Sun, Feb 14, 2021 at 06:06:12PM +0000, Jonathan Cameron wrote:
> On Fri, 12 Feb 2021 21:13:41 +0900
> William Breathitt Gray <vilhelm.gray at gmail.com> wrote:
> 
> > This patch introduces a character device interface for the Counter
> > subsystem. Device data is exposed through standard character device read
> > operations. Device data is gathered when a Counter event is pushed by
> > the respective Counter device driver. Configuration is handled via ioctl
> > operations on the respective Counter character device node.
> > 
> > Cc: David Lechner <david at lechnology.com>
> > Cc: Gwendal Grignou <gwendal at chromium.org>
> > Cc: Dan Carpenter <dan.carpenter at oracle.com>
> > Cc: Oleksij Rempel <o.rempel at pengutronix.de>
> > Signed-off-by: William Breathitt Gray <vilhelm.gray at gmail.com>
> 
> Hi William,
> 
> A few minor comments.  Mostly seems to have come together well and
> makes sense to me.
> 
> Jonathan
> 
> > ---
> >  drivers/counter/Makefile         |   2 +-
> >  drivers/counter/counter-chrdev.c | 496 +++++++++++++++++++++++++++++++
> >  drivers/counter/counter-chrdev.h |  16 +
> >  drivers/counter/counter-core.c   |  37 ++-
> >  include/linux/counter.h          |  45 +++
> >  include/uapi/linux/counter.h     |  70 +++++
> >  6 files changed, 661 insertions(+), 5 deletions(-)
> >  create mode 100644 drivers/counter/counter-chrdev.c
> >  create mode 100644 drivers/counter/counter-chrdev.h
> > 
> 
> ...
> 
> > diff --git a/drivers/counter/counter-core.c b/drivers/counter/counter-core.c
> > index bcf672e1fc0d..c137fcb97d9c 100644
> > --- a/drivers/counter/counter-core.c
> > +++ b/drivers/counter/counter-core.c
> > @@ -5,12 +5,16 @@
> >   */
> >  #include <linux/counter.h>
> >  #include <linux/device.h>
> > +#include <linux/device/bus.h>
> >  #include <linux/export.h>
> > +#include <linux/fs.h>
> >  #include <linux/gfp.h>
> >  #include <linux/idr.h>
> >  #include <linux/init.h>
> >  #include <linux/module.h>
> > +#include <linux/types.h>
> >  
> > +#include "counter-chrdev.h"
> >  #include "counter-sysfs.h"
> >  
> >  /* Provides a unique ID for each counter device */
> > @@ -33,6 +37,8 @@ static struct bus_type counter_bus_type = {
> >  	.name = "counter"
> >  };
> >  
> > +static dev_t counter_devt;
> > +
> >  /**
> >   * counter_register - register Counter to the system
> >   * @counter:	pointer to Counter to register
> > @@ -54,7 +60,6 @@ int counter_register(struct counter_device *const counter)
> >  	if (counter->id < 0)
> >  		return counter->id;
> >  
> > -	/* Configure device structure for Counter */
> 
> Not sure why this comment gets removed here.

This comment wasn't suppose to be removed. I'll revert this.

> >  	dev->type = &counter_device_type;
> >  	dev->bus = &counter_bus_type;
> >  	if (counter->parent) {
> > @@ -65,18 +70,25 @@ int counter_register(struct counter_device *const counter)
> >  	device_initialize(dev);
> >  	dev_set_drvdata(dev, counter);
> >  
> > +	/* Add Counter character device */
> > +	err = counter_chrdev_add(counter, counter_devt);
> > +	if (err < 0)
> > +		goto err_free_id;
> > +
> >  	/* Add Counter sysfs attributes */
> >  	err = counter_sysfs_add(counter);
> >  	if (err < 0)
> > -		goto err_free_id;
> > +		goto err_remove_chrdev;
> >  
> >  	/* Add device to system */
> >  	err = device_add(dev);
> >  	if (err < 0)
> > -		goto err_free_id;
> > +		goto err_remove_chrdev;
> 
> It might be worth thinking about using cdev_device_add()
> though will require a slightly different order of adding.

I think using cdev_device_add() should be possible. I'll adjust
counter_chrdev_add() accordingly to account for this.
 
> >  
> >  	return 0;
> >  
> > +err_remove_chrdev:
> > +	counter_chrdev_remove(counter);
> >  err_free_id:
> >  	put_device(dev);
> >  	return err;
> > @@ -138,13 +150,30 @@ int devm_counter_register(struct device *dev,
> >  }
> >  EXPORT_SYMBOL_GPL(devm_counter_register);
> >  
> > +#define COUNTER_DEV_MAX 256
> > +
> >  static int __init counter_init(void)
> >  {
> > -	return bus_register(&counter_bus_type);
> > +	int err;
> > +
> > +	err = bus_register(&counter_bus_type);
> > +	if (err < 0)
> > +		return err;
> > +
> > +	err = alloc_chrdev_region(&counter_devt, 0, COUNTER_DEV_MAX, "counter");
> > +	if (err < 0)
> > +		goto err_unregister_bus;
> > +
> > +	return 0;
> > +
> > +err_unregister_bus:
> > +	bus_unregister(&counter_bus_type);
> > +	return err;
> >  }
> >  
> >  static void __exit counter_exit(void)
> >  {
> > +	unregister_chrdev_region(counter_devt, COUNTER_DEV_MAX);
> >  	bus_unregister(&counter_bus_type);
> >  }
> >  
> 
> ...
> 
> > diff --git a/include/uapi/linux/counter.h b/include/uapi/linux/counter.h
> > index 6113938a6044..3d647a5383b8 100644
> > --- a/include/uapi/linux/counter.h
> > +++ b/include/uapi/linux/counter.h
> > @@ -6,6 +6,19 @@
> >  #ifndef _UAPI_COUNTER_H_
> >  #define _UAPI_COUNTER_H_
> >  
> > +#include <linux/ioctl.h>
> > +#include <linux/types.h>
> > +
> > +/* Component type definitions */
> > +enum counter_component_type {
> > +	COUNTER_COMPONENT_NONE,
> > +	COUNTER_COMPONENT_SIGNAL,
> > +	COUNTER_COMPONENT_COUNT,
> > +	COUNTER_COMPONENT_FUNCTION,
> > +	COUNTER_COMPONENT_SYNAPSE_ACTION,
> > +	COUNTER_COMPONENT_EXTENSION,
> > +};
> > +
> >  /* Component scope definitions */
> >  enum counter_scope {
> >  	COUNTER_SCOPE_DEVICE,
> > @@ -13,6 +26,63 @@ enum counter_scope {
> >  	COUNTER_SCOPE_COUNT,
> >  };
> >  
> > +/**
> > + * struct counter_component - Counter component identification
> > + * @type: component type (one of enum counter_component_type)
> > + * @scope: component scope (one of enum counter_scope)
> > + * @parent: parent component ID (matching the Y/Z suffix of the respective sysfs
> > + *	    path as described in Documentation/ABI/testing/sysfs-bus-counter)
> 
> Probably good to give an example here as well as the cross reference.

Ack.

William Breathitt Gray
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