[RFC 0/4] counter: Simplify count_read/count_write/signal_read

[RFC 0/4] counter: Simplify count_read/count_write/signal_read

[William Breathitt Gray]

I have a simplification for the the Counter subsystem callbacks, but I
want to get some comments first before committing further. Since this is
an RFC, I've included updates to the 104-QUAD-8 driver here for the
sake of demonstration; if the comments received are positive, I'll
submit the changes for the rest of the existing counter drivers as well.

The changes in this patchset will not affect the userspace interface.
Rather, these changes are intended to simplify the kernelspace Counter
callbacks for counter device driver authors.

The following main changes are proposed:

* Retire the opaque counter_count_read_value/counter_count_write_value
  structures and simply represent count data as an unsigned integer.

* Retire the opaque counter_signal_read_value structure and represent
  Signal data as a counter_signal_value enum.

These changes should reduce some complexity and code in the use and
implementation of the count_read, count_write, and signal_read
callbacks.

The opaque structures for Count data and Signal data were introduced
originally in anticipation of supporting various representations of
counter data (e.g. arbitrary-precision tallies, floating-point spherical
coordinate positions, etc). However, with the counter device drivers
that have appeared, it's become apparent that utilizing opaque
structures in kernelspace is not the best approach to take.

I believe it is best to let userspace applications decide how to
interpret the count data they receive. There are a couple of reasons why
it would be good to do so:

* Users use their devices in unexpected ways.

  For example, a quadrature encoder counter device is typically used to
  keep track of the position of a motor, but a user could set the device
  in a pulse-direction mode and instead use it to count sporadic rising
  edges from an arbitrary signal line unrelated to positioning. Users
  should have the freedom to decide what their data represents.

* Most counter devices represent data as unsigned integers anyway.

  For example, whether the device is a tally counter or position
  counter, the count data is represented to the user as an unsigned
  integer value. So specifying that one device is representing tallies
  while the other specifies positions does not provide much utility from
  an interface perspective.

For these reasons, the count_read and count_write callbacks have been
redefined to pass count data directly as unsigned long instead of passed
via opaque structures:

        count_read(struct counter_device *counter,
                   struct counter_count *count, unsigned long *val);
        count_write(struct counter_device *counter,
                    struct counter_count *count, unsigned long val);

Similarly, the signal_read is redefined to pass Signal data directly as
a counter_signal_value enum instead of via an opaque structure:

        signal_read(struct counter_device *counter,
                    struct counter_signal *signal,
                    enum counter_signal_value *val);

The counter_signal_value enum is simply the counter_signal_level enum
redefined to remove the references to the Signal data "level" data type.

William Breathitt Gray (4):
  counter: Simplify the count_read and count_write callbacks
  counter: Simplify the signal_read callback
  docs: driver-api: generic-counter: Update Count and Signal data types
  counter: 104-quad-8: Update count_read/count_write/signal_read
    callbacks

 Documentation/driver-api/generic-counter.rst |  22 ++--
 drivers/counter/104-quad-8.c                 |  33 ++----
 drivers/counter/counter.c                    | 101 +++----------------
 include/linux/counter.h                      |  74 ++------------
 4 files changed, 42 insertions(+), 188 deletions(-)

-- 
2.23.0

[RFC 1/4] counter: Simplify the count_read and count_write callbacks

[William Breathitt Gray]

The count_read and count_write callbacks are simplified to pass val as
unsigned long rather than as an opaque data structure. The opaque
counter_count_read_value and counter_count_write_value structures,
counter_count_value_type enum, and relevant counter_count_read_value_set
and counter_count_write_value_get functions, are removed as they are no
longer used.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 drivers/counter/counter.c | 66 +++++----------------------------------
 include/linux/counter.h   | 43 +++----------------------
 2 files changed, 12 insertions(+), 97 deletions(-)

diff --git a/drivers/counter/counter.c b/drivers/counter/counter.c
index 106bc7180cd8..1d08f1437b1b 100644
--- a/drivers/counter/counter.c
+++ b/drivers/counter/counter.c
@@ -246,60 +246,6 @@ void counter_signal_read_value_set(struct counter_signal_read_value *const val,
 }
 EXPORT_SYMBOL_GPL(counter_signal_read_value_set);
 
-/**
- * counter_count_read_value_set - set counter_count_read_value data
- * @val:	counter_count_read_value structure to set
- * @type:	property Count data represents
- * @data:	Count data
- *
- * This function sets an opaque counter_count_read_value structure with the
- * provided Count data.
- */
-void counter_count_read_value_set(struct counter_count_read_value *const val,
-				  const enum counter_count_value_type type,
-				  void *const data)
-{
-	switch (type) {
-	case COUNTER_COUNT_POSITION:
-		val->len = sprintf(val->buf, "%lu\n", *(unsigned long *)data);
-		break;
-	default:
-		val->len = 0;
-	}
-}
-EXPORT_SYMBOL_GPL(counter_count_read_value_set);
-
-/**
- * counter_count_write_value_get - get counter_count_write_value data
- * @data:	Count data
- * @type:	property Count data represents
- * @val:	counter_count_write_value structure containing data
- *
- * This function extracts Count data from the provided opaque
- * counter_count_write_value structure and stores it at the address provided by
- * @data.
- *
- * RETURNS:
- * 0 on success, negative error number on failure.
- */
-int counter_count_write_value_get(void *const data,
-				  const enum counter_count_value_type type,
-				  const struct counter_count_write_value *const val)
-{
-	int err;
-
-	switch (type) {
-	case COUNTER_COUNT_POSITION:
-		err = kstrtoul(val->buf, 0, data);
-		if (err)
-			return err;
-		break;
-	}
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(counter_count_write_value_get);
-
 struct counter_attr_parm {
 	struct counter_device_attr_group *group;
 	const char *prefix;
@@ -788,13 +734,13 @@ static ssize_t counter_count_show(struct device *dev,
 	const struct counter_count_unit *const component = devattr->component;
 	struct counter_count *const count = component->count;
 	int err;
-	struct counter_count_read_value val = { .buf = buf };
+	unsigned long val;
 
 	err = counter->ops->count_read(counter, count, &val);
 	if (err)
 		return err;
 
-	return val.len;
+	return sprintf(buf, "%lu\n", val);
 }
 
 static ssize_t counter_count_store(struct device *dev,
@@ -806,9 +752,13 @@ static ssize_t counter_count_store(struct device *dev,
 	const struct counter_count_unit *const component = devattr->component;
 	struct counter_count *const count = component->count;
 	int err;
-	struct counter_count_write_value val = { .buf = buf };
+	unsigned long val;
+
+	err = kstrtoul(buf, 0, &val);
+	if (err)
+		return err;
 
-	err = counter->ops->count_write(counter, count, &val);
+	err = counter->ops->count_write(counter, count, val);
 	if (err)
 		return err;
 
diff --git a/include/linux/counter.h b/include/linux/counter.h
index a061cdcdef7c..7e40796598a6 100644
--- a/include/linux/counter.h
+++ b/include/linux/counter.h
@@ -300,24 +300,6 @@ struct counter_signal_read_value {
 	size_t len;
 };
 
-/**
- * struct counter_count_read_value - Opaque Count read value
- * @buf:	string representation of Count read value
- * @len:	length of string in @buf
- */
-struct counter_count_read_value {
-	char *buf;
-	size_t len;
-};
-
-/**
- * struct counter_count_write_value - Opaque Count write value
- * @buf:	string representation of Count write value
- */
-struct counter_count_write_value {
-	const char *buf;
-};
-
 /**
  * struct counter_ops - Callbacks from driver
  * @signal_read:	optional read callback for Signal attribute. The read
@@ -328,15 +310,10 @@ struct counter_count_write_value {
  *			signal_read callback.
  * @count_read:		optional read callback for Count attribute. The read
  *			value of the respective Count should be passed back via
- *			the val parameter. val points to an opaque type which
- *			should be set only by calling the
- *			counter_count_read_value_set function from within the
- *			count_read callback.
+ *			the val parameter.
  * @count_write:	optional write callback for Count attribute. The write
  *			value for the respective Count is passed in via the val
- *			parameter. val points to an opaque type which should be
- *			accessed only by calling the
- *			counter_count_write_value_get function.
+ *			parameter.
  * @function_get:	function to get the current count function mode. Returns
  *			0 on success and negative error code on error. The index
  *			of the respective Count's returned function mode should
@@ -357,11 +334,9 @@ struct counter_ops {
 			   struct counter_signal *signal,
 			   struct counter_signal_read_value *val);
 	int (*count_read)(struct counter_device *counter,
-			  struct counter_count *count,
-			  struct counter_count_read_value *val);
+			  struct counter_count *count, unsigned long *val);
 	int (*count_write)(struct counter_device *counter,
-			   struct counter_count *count,
-			   struct counter_count_write_value *val);
+			   struct counter_count *count, unsigned long val);
 	int (*function_get)(struct counter_device *counter,
 			    struct counter_count *count, size_t *function);
 	int (*function_set)(struct counter_device *counter,
@@ -486,19 +461,9 @@ enum counter_signal_value_type {
 	COUNTER_SIGNAL_LEVEL = 0
 };
 
-enum counter_count_value_type {
-	COUNTER_COUNT_POSITION = 0,
-};
-
 void counter_signal_read_value_set(struct counter_signal_read_value *const val,
 				   const enum counter_signal_value_type type,
 				   void *const data);
-void counter_count_read_value_set(struct counter_count_read_value *const val,
-				  const enum counter_count_value_type type,
-				  void *const data);
-int counter_count_write_value_get(void *const data,
-				  const enum counter_count_value_type type,
-				  const struct counter_count_write_value *const val);
 
 int counter_register(struct counter_device *const counter);
 void counter_unregister(struct counter_device *const counter);
-- 
2.23.0

[RFC 2/4] counter: Simplify the signal_read callback

[William Breathitt Gray]

The signal_read callback is simplified to pass val as a
counter_signal_val enum rather than as an opaque data structure. The
opaque counter_signal_read_value structure and relevant
counter_signal_read_value_set function are removed as they are no longer
used. In addition, the counter_signal_level enum is replaced by the
similar counter_signal_value enum.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 drivers/counter/counter.c | 35 +++++++----------------------------
 include/linux/counter.h   | 31 +++++--------------------------
 2 files changed, 12 insertions(+), 54 deletions(-)

diff --git a/drivers/counter/counter.c b/drivers/counter/counter.c
index 1d08f1437b1b..6a683d086008 100644
--- a/drivers/counter/counter.c
+++ b/drivers/counter/counter.c
@@ -220,32 +220,6 @@ ssize_t counter_device_enum_available_read(struct counter_device *counter,
 }
 EXPORT_SYMBOL_GPL(counter_device_enum_available_read);
 
-static const char *const counter_signal_level_str[] = {
-	[COUNTER_SIGNAL_LEVEL_LOW] = "low",
-	[COUNTER_SIGNAL_LEVEL_HIGH] = "high"
-};
-
-/**
- * counter_signal_read_value_set - set counter_signal_read_value data
- * @val:	counter_signal_read_value structure to set
- * @type:	property Signal data represents
- * @data:	Signal data
- *
- * This function sets an opaque counter_signal_read_value structure with the
- * provided Signal data.
- */
-void counter_signal_read_value_set(struct counter_signal_read_value *const val,
-				   const enum counter_signal_value_type type,
-				   void *const data)
-{
-	if (type == COUNTER_SIGNAL_LEVEL)
-		val->len = sprintf(val->buf, "%s\n",
-				   counter_signal_level_str[*(enum counter_signal_level *)data]);
-	else
-		val->len = 0;
-}
-EXPORT_SYMBOL_GPL(counter_signal_read_value_set);
-
 struct counter_attr_parm {
 	struct counter_device_attr_group *group;
 	const char *prefix;
@@ -315,6 +289,11 @@ struct counter_signal_unit {
 	struct counter_signal *signal;
 };
 
+static const char *const counter_signal_value_str[] = {
+	[COUNTER_SIGNAL_LOW] = "low",
+	[COUNTER_SIGNAL_HIGH] = "high"
+};
+
 static ssize_t counter_signal_show(struct device *dev,
 				   struct device_attribute *attr, char *buf)
 {
@@ -323,13 +302,13 @@ static ssize_t counter_signal_show(struct device *dev,
 	const struct counter_signal_unit *const component = devattr->component;
 	struct counter_signal *const signal = component->signal;
 	int err;
-	struct counter_signal_read_value val = { .buf = buf };
+	enum counter_signal_value val;
 
 	err = counter->ops->signal_read(counter, signal, &val);
 	if (err)
 		return err;
 
-	return val.len;
+	return sprintf(buf, "%s\n", counter_signal_value_str[val]);
 }
 
 struct counter_name_unit {
diff --git a/include/linux/counter.h b/include/linux/counter.h
index 7e40796598a6..32fb4d8cc3fd 100644
--- a/include/linux/counter.h
+++ b/include/linux/counter.h
@@ -290,24 +290,16 @@ struct counter_device_state {
 	const struct attribute_group **groups;
 };
 
-/**
- * struct counter_signal_read_value - Opaque Signal read value
- * @buf:	string representation of Signal read value
- * @len:	length of string in @buf
- */
-struct counter_signal_read_value {
-	char *buf;
-	size_t len;
+enum counter_signal_value {
+	COUNTER_SIGNAL_LOW = 0,
+	COUNTER_SIGNAL_HIGH
 };
 
 /**
  * struct counter_ops - Callbacks from driver
  * @signal_read:	optional read callback for Signal attribute. The read
  *			value of the respective Signal should be passed back via
- *			the val parameter. val points to an opaque type which
- *			should be set only by calling the
- *			counter_signal_read_value_set function from within the
- *			signal_read callback.
+ *			the val parameter.
  * @count_read:		optional read callback for Count attribute. The read
  *			value of the respective Count should be passed back via
  *			the val parameter.
@@ -332,7 +324,7 @@ struct counter_signal_read_value {
 struct counter_ops {
 	int (*signal_read)(struct counter_device *counter,
 			   struct counter_signal *signal,
-			   struct counter_signal_read_value *val);
+			   enum counter_signal_value *val);
 	int (*count_read)(struct counter_device *counter,
 			  struct counter_count *count, unsigned long *val);
 	int (*count_write)(struct counter_device *counter,
@@ -452,19 +444,6 @@ struct counter_device {
 	void *priv;
 };
 
-enum counter_signal_level {
-	COUNTER_SIGNAL_LEVEL_LOW = 0,
-	COUNTER_SIGNAL_LEVEL_HIGH
-};
-
-enum counter_signal_value_type {
-	COUNTER_SIGNAL_LEVEL = 0
-};
-
-void counter_signal_read_value_set(struct counter_signal_read_value *const val,
-				   const enum counter_signal_value_type type,
-				   void *const data);
-
 int counter_register(struct counter_device *const counter);
 void counter_unregister(struct counter_device *const counter);
 int devm_counter_register(struct device *dev,
-- 
2.23.0

[RFC 3/4] docs: driver-api: generic-counter: Update Count and Signal data types

[William Breathitt Gray]

Count data is now always represented as an unsigned integer, while
Signal data is either SIGNAL_LOW or SIGNAL_HIGH.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 Documentation/driver-api/generic-counter.rst | 22 +++++++-------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst
index 8382f01a53e3..161652fc1025 100644
--- a/Documentation/driver-api/generic-counter.rst
+++ b/Documentation/driver-api/generic-counter.rst
@@ -39,10 +39,7 @@ There are three core components to a counter:
 COUNT
 -----
 A Count represents the count data for a set of Signals. The Generic
-Counter interface provides the following available count data types:
-
-* COUNT_POSITION:
-  Unsigned integer value representing position.
+Counter interface represents the count data as an unsigned integer.
 
 A Count has a count function mode which represents the update behavior
 for the count data. The Generic Counter interface provides the following
@@ -93,19 +90,16 @@ SIGNAL
 A Signal represents a counter input data; this is the input data that is
 evaluated by the counter to determine the count data; e.g. a quadrature
 signal output line of a rotary encoder. Not all counter devices provide
-user access to the Signal data.
-
-The Generic Counter interface provides the following available signal
-data types for when the Signal data is available for user access:
+user access to the Signal data, so exposure is optional for drivers.
 
-* SIGNAL_LEVEL:
-  Signal line state level. The following states are possible:
+When the Signal data is available for user access, the Generic Counter
+interface provides the following available signal values:
 
-  - SIGNAL_LEVEL_LOW:
-    Signal line is in a low state.
+* SIGNAL_LOW:
+  Signal line is in a low state.
 
-  - SIGNAL_LEVEL_HIGH:
-    Signal line is in a high state.
+* SIGNAL_HIGH:
+  Signal line is in a high state.
 
 A Signal may be associated with one or more Counts.
 
-- 
2.23.0

[RFC 4/4] counter: 104-quad-8: Update count_read/count_write/signal_read callbacks

[William Breathitt Gray]

The count_read and count_write callbacks pass unsigned long now, while
the signal_read callback passes an enum counter_signal_value.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 drivers/counter/104-quad-8.c | 33 ++++++++++-----------------------
 1 file changed, 10 insertions(+), 23 deletions(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 00b113f4b958..17e67a84777d 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -562,11 +562,10 @@ static const struct iio_chan_spec quad8_channels[] = {
 };
 
 static int quad8_signal_read(struct counter_device *counter,
-	struct counter_signal *signal, struct counter_signal_read_value *val)
+	struct counter_signal *signal, enum counter_signal_value *val)
 {
 	const struct quad8_iio *const priv = counter->priv;
 	unsigned int state;
-	enum counter_signal_level level;
 
 	/* Only Index signal levels can be read */
 	if (signal->id < 16)
@@ -575,22 +574,19 @@ static int quad8_signal_read(struct counter_device *counter,
 	state = inb(priv->base + QUAD8_REG_INDEX_INPUT_LEVELS)
 		& BIT(signal->id - 16);
 
-	level = (state) ? COUNTER_SIGNAL_LEVEL_HIGH : COUNTER_SIGNAL_LEVEL_LOW;
-
-	counter_signal_read_value_set(val, COUNTER_SIGNAL_LEVEL, &level);
+	*val = (state) ? COUNTER_SIGNAL_HIGH : COUNTER_SIGNAL_LOW;
 
 	return 0;
 }
 
 static int quad8_count_read(struct counter_device *counter,
-	struct counter_count *count, struct counter_count_read_value *val)
+	struct counter_count *count, unsigned long *val)
 {
 	const struct quad8_iio *const priv = counter->priv;
 	const int base_offset = priv->base + 2 * count->id;
 	unsigned int flags;
 	unsigned int borrow;
 	unsigned int carry;
-	unsigned long position;
 	int i;
 
 	flags = inb(base_offset + 1);
@@ -598,36 +594,27 @@ static int quad8_count_read(struct counter_device *counter,
 	carry = !!(flags & QUAD8_FLAG_CT);
 
 	/* Borrow XOR Carry effectively doubles count range */
-	position = (unsigned long)(borrow ^ carry) << 24;
+	*val = (unsigned long)(borrow ^ carry) << 24;
 
 	/* Reset Byte Pointer; transfer Counter to Output Latch */
 	outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_CNTR_OUT,
 	     base_offset + 1);
 
 	for (i = 0; i < 3; i++)
-		position |= (unsigned long)inb(base_offset) << (8 * i);
-
-	counter_count_read_value_set(val, COUNTER_COUNT_POSITION, &position);
+		*val |= (unsigned long)inb(base_offset) << (8 * i);
 
 	return 0;
 }
 
 static int quad8_count_write(struct counter_device *counter,
-	struct counter_count *count, struct counter_count_write_value *val)
+	struct counter_count *count, unsigned long val)
 {
 	const struct quad8_iio *const priv = counter->priv;
 	const int base_offset = priv->base + 2 * count->id;
-	int err;
-	unsigned long position;
 	int i;
 
-	err = counter_count_write_value_get(&position, COUNTER_COUNT_POSITION,
-					    val);
-	if (err)
-		return err;
-
 	/* Only 24-bit values are supported */
-	if (position > 0xFFFFFF)
+	if (val > 0xFFFFFF)
 		return -EINVAL;
 
 	/* Reset Byte Pointer */
@@ -635,7 +622,7 @@ static int quad8_count_write(struct counter_device *counter,
 
 	/* Counter can only be set via Preset Register */
 	for (i = 0; i < 3; i++)
-		outb(position >> (8 * i), base_offset);
+		outb(val >> (8 * i), base_offset);
 
 	/* Transfer Preset Register to Counter */
 	outb(QUAD8_CTR_RLD | QUAD8_RLD_PRESET_CNTR, base_offset + 1);
@@ -644,9 +631,9 @@ static int quad8_count_write(struct counter_device *counter,
 	outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP, base_offset + 1);
 
 	/* Set Preset Register back to original value */
-	position = priv->preset[count->id];
+	val = priv->preset[count->id];
 	for (i = 0; i < 3; i++)
-		outb(position >> (8 * i), base_offset);
+		outb(val >> (8 * i), base_offset);
 
 	/* Reset Borrow, Carry, Compare, and Sign flags */
 	outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_FLAGS, base_offset + 1);
-- 
2.23.0

Re: [RFC 1/4] counter: Simplify the count_read and count_write callbacks

[Jonathan Cameron]

On Sun, 15 Sep 2019 14:57:56 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> The count_read and count_write callbacks are simplified to pass val as
> unsigned long rather than as an opaque data structure. The opaque
> counter_count_read_value and counter_count_write_value structures,
> counter_count_value_type enum, and relevant counter_count_read_value_set
> and counter_count_write_value_get functions, are removed as they are no
> longer used.
> 
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>

Seems like a sensible bit of excessive abstraction removal to me.  I'm not
totally sure why these got so complex in the first place though.

Can you recall the reason as it might help to judge why we no longer
think the same?

Thanks,

Jonathan
> ---
>  drivers/counter/counter.c | 66 +++++----------------------------------
>  include/linux/counter.h   | 43 +++----------------------
>  2 files changed, 12 insertions(+), 97 deletions(-)
> 
> diff --git a/drivers/counter/counter.c b/drivers/counter/counter.c
> index 106bc7180cd8..1d08f1437b1b 100644
> --- a/drivers/counter/counter.c
> +++ b/drivers/counter/counter.c
> @@ -246,60 +246,6 @@ void counter_signal_read_value_set(struct counter_signal_read_value *const val,
>  }
>  EXPORT_SYMBOL_GPL(counter_signal_read_value_set);
>  
> -/**
> - * counter_count_read_value_set - set counter_count_read_value data
> - * @val:	counter_count_read_value structure to set
> - * @type:	property Count data represents
> - * @data:	Count data
> - *
> - * This function sets an opaque counter_count_read_value structure with the
> - * provided Count data.
> - */
> -void counter_count_read_value_set(struct counter_count_read_value *const val,
> -				  const enum counter_count_value_type type,
> -				  void *const data)
> -{
> -	switch (type) {
> -	case COUNTER_COUNT_POSITION:
> -		val->len = sprintf(val->buf, "%lu\n", *(unsigned long *)data);
> -		break;
> -	default:
> -		val->len = 0;
> -	}
> -}
> -EXPORT_SYMBOL_GPL(counter_count_read_value_set);
> -
> -/**
> - * counter_count_write_value_get - get counter_count_write_value data
> - * @data:	Count data
> - * @type:	property Count data represents
> - * @val:	counter_count_write_value structure containing data
> - *
> - * This function extracts Count data from the provided opaque
> - * counter_count_write_value structure and stores it at the address provided by
> - * @data.
> - *
> - * RETURNS:
> - * 0 on success, negative error number on failure.
> - */
> -int counter_count_write_value_get(void *const data,
> -				  const enum counter_count_value_type type,
> -				  const struct counter_count_write_value *const val)
> -{
> -	int err;
> -
> -	switch (type) {
> -	case COUNTER_COUNT_POSITION:
> -		err = kstrtoul(val->buf, 0, data);
> -		if (err)
> -			return err;
> -		break;
> -	}
> -
> -	return 0;
> -}
> -EXPORT_SYMBOL_GPL(counter_count_write_value_get);
> -
>  struct counter_attr_parm {
>  	struct counter_device_attr_group *group;
>  	const char *prefix;
> @@ -788,13 +734,13 @@ static ssize_t counter_count_show(struct device *dev,
>  	const struct counter_count_unit *const component = devattr->component;
>  	struct counter_count *const count = component->count;
>  	int err;
> -	struct counter_count_read_value val = { .buf = buf };
> +	unsigned long val;
>  
>  	err = counter->ops->count_read(counter, count, &val);
>  	if (err)
>  		return err;
>  
> -	return val.len;
> +	return sprintf(buf, "%lu\n", val);
>  }
>  
>  static ssize_t counter_count_store(struct device *dev,
> @@ -806,9 +752,13 @@ static ssize_t counter_count_store(struct device *dev,
>  	const struct counter_count_unit *const component = devattr->component;
>  	struct counter_count *const count = component->count;
>  	int err;
> -	struct counter_count_write_value val = { .buf = buf };
> +	unsigned long val;
> +
> +	err = kstrtoul(buf, 0, &val);
> +	if (err)
> +		return err;
>  
> -	err = counter->ops->count_write(counter, count, &val);
> +	err = counter->ops->count_write(counter, count, val);
>  	if (err)
>  		return err;
>  
> diff --git a/include/linux/counter.h b/include/linux/counter.h
> index a061cdcdef7c..7e40796598a6 100644
> --- a/include/linux/counter.h
> +++ b/include/linux/counter.h
> @@ -300,24 +300,6 @@ struct counter_signal_read_value {
>  	size_t len;
>  };
>  
> -/**
> - * struct counter_count_read_value - Opaque Count read value
> - * @buf:	string representation of Count read value
> - * @len:	length of string in @buf
> - */
> -struct counter_count_read_value {
> -	char *buf;
> -	size_t len;
> -};
> -
> -/**
> - * struct counter_count_write_value - Opaque Count write value
> - * @buf:	string representation of Count write value
> - */
> -struct counter_count_write_value {
> -	const char *buf;
> -};
> -
>  /**
>   * struct counter_ops - Callbacks from driver
>   * @signal_read:	optional read callback for Signal attribute. The read
> @@ -328,15 +310,10 @@ struct counter_count_write_value {
>   *			signal_read callback.
>   * @count_read:		optional read callback for Count attribute. The read
>   *			value of the respective Count should be passed back via
> - *			the val parameter. val points to an opaque type which
> - *			should be set only by calling the
> - *			counter_count_read_value_set function from within the
> - *			count_read callback.
> + *			the val parameter.
>   * @count_write:	optional write callback for Count attribute. The write
>   *			value for the respective Count is passed in via the val
> - *			parameter. val points to an opaque type which should be
> - *			accessed only by calling the
> - *			counter_count_write_value_get function.
> + *			parameter.
>   * @function_get:	function to get the current count function mode. Returns
>   *			0 on success and negative error code on error. The index
>   *			of the respective Count's returned function mode should
> @@ -357,11 +334,9 @@ struct counter_ops {
>  			   struct counter_signal *signal,
>  			   struct counter_signal_read_value *val);
>  	int (*count_read)(struct counter_device *counter,
> -			  struct counter_count *count,
> -			  struct counter_count_read_value *val);
> +			  struct counter_count *count, unsigned long *val);
>  	int (*count_write)(struct counter_device *counter,
> -			   struct counter_count *count,
> -			   struct counter_count_write_value *val);
> +			   struct counter_count *count, unsigned long val);
>  	int (*function_get)(struct counter_device *counter,
>  			    struct counter_count *count, size_t *function);
>  	int (*function_set)(struct counter_device *counter,
> @@ -486,19 +461,9 @@ enum counter_signal_value_type {
>  	COUNTER_SIGNAL_LEVEL = 0
>  };
>  
> -enum counter_count_value_type {
> -	COUNTER_COUNT_POSITION = 0,
> -};
> -
>  void counter_signal_read_value_set(struct counter_signal_read_value *const val,
>  				   const enum counter_signal_value_type type,
>  				   void *const data);
> -void counter_count_read_value_set(struct counter_count_read_value *const val,
> -				  const enum counter_count_value_type type,
> -				  void *const data);
> -int counter_count_write_value_get(void *const data,
> -				  const enum counter_count_value_type type,
> -				  const struct counter_count_write_value *const val);
>  
>  int counter_register(struct counter_device *const counter);
>  void counter_unregister(struct counter_device *const counter);

Re: [RFC 1/4] counter: Simplify the count_read and count_write callbacks

[Jonathan Cameron]

On Sun, 15 Sep 2019 14:39:17 +0100
Jonathan Cameron <jic23@jic23.retrosnub.co.uk> wrote:

> On Sun, 15 Sep 2019 14:57:56 +0900
> William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> 
> > The count_read and count_write callbacks are simplified to pass val as
> > unsigned long rather than as an opaque data structure. The opaque
> > counter_count_read_value and counter_count_write_value structures,
> > counter_count_value_type enum, and relevant counter_count_read_value_set
> > and counter_count_write_value_get functions, are removed as they are no
> > longer used.
> > 
> > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>  
> 
> Seems like a sensible bit of excessive abstraction removal to me.  I'm not
> totally sure why these got so complex in the first place though.
Ah. I should have read the cover letter rather than just diving in the code :)
All explained there I see.

> 
> Can you recall the reason as it might help to judge why we no longer
> think the same?
> 
> Thanks,
> 
> Jonathan
> > ---
> >  drivers/counter/counter.c | 66 +++++----------------------------------
> >  include/linux/counter.h   | 43 +++----------------------
> >  2 files changed, 12 insertions(+), 97 deletions(-)
> > 
> > diff --git a/drivers/counter/counter.c b/drivers/counter/counter.c
> > index 106bc7180cd8..1d08f1437b1b 100644
> > --- a/drivers/counter/counter.c
> > +++ b/drivers/counter/counter.c
> > @@ -246,60 +246,6 @@ void counter_signal_read_value_set(struct counter_signal_read_value *const val,
> >  }
> >  EXPORT_SYMBOL_GPL(counter_signal_read_value_set);
> >  
> > -/**
> > - * counter_count_read_value_set - set counter_count_read_value data
> > - * @val:	counter_count_read_value structure to set
> > - * @type:	property Count data represents
> > - * @data:	Count data
> > - *
> > - * This function sets an opaque counter_count_read_value structure with the
> > - * provided Count data.
> > - */
> > -void counter_count_read_value_set(struct counter_count_read_value *const val,
> > -				  const enum counter_count_value_type type,
> > -				  void *const data)
> > -{
> > -	switch (type) {
> > -	case COUNTER_COUNT_POSITION:
> > -		val->len = sprintf(val->buf, "%lu\n", *(unsigned long *)data);
> > -		break;
> > -	default:
> > -		val->len = 0;
> > -	}
> > -}
> > -EXPORT_SYMBOL_GPL(counter_count_read_value_set);
> > -
> > -/**
> > - * counter_count_write_value_get - get counter_count_write_value data
> > - * @data:	Count data
> > - * @type:	property Count data represents
> > - * @val:	counter_count_write_value structure containing data
> > - *
> > - * This function extracts Count data from the provided opaque
> > - * counter_count_write_value structure and stores it at the address provided by
> > - * @data.
> > - *
> > - * RETURNS:
> > - * 0 on success, negative error number on failure.
> > - */
> > -int counter_count_write_value_get(void *const data,
> > -				  const enum counter_count_value_type type,
> > -				  const struct counter_count_write_value *const val)
> > -{
> > -	int err;
> > -
> > -	switch (type) {
> > -	case COUNTER_COUNT_POSITION:
> > -		err = kstrtoul(val->buf, 0, data);
> > -		if (err)
> > -			return err;
> > -		break;
> > -	}
> > -
> > -	return 0;
> > -}
> > -EXPORT_SYMBOL_GPL(counter_count_write_value_get);
> > -
> >  struct counter_attr_parm {
> >  	struct counter_device_attr_group *group;
> >  	const char *prefix;
> > @@ -788,13 +734,13 @@ static ssize_t counter_count_show(struct device *dev,
> >  	const struct counter_count_unit *const component = devattr->component;
> >  	struct counter_count *const count = component->count;
> >  	int err;
> > -	struct counter_count_read_value val = { .buf = buf };
> > +	unsigned long val;
> >  
> >  	err = counter->ops->count_read(counter, count, &val);
> >  	if (err)
> >  		return err;
> >  
> > -	return val.len;
> > +	return sprintf(buf, "%lu\n", val);
> >  }
> >  
> >  static ssize_t counter_count_store(struct device *dev,
> > @@ -806,9 +752,13 @@ static ssize_t counter_count_store(struct device *dev,
> >  	const struct counter_count_unit *const component = devattr->component;
> >  	struct counter_count *const count = component->count;
> >  	int err;
> > -	struct counter_count_write_value val = { .buf = buf };
> > +	unsigned long val;
> > +
> > +	err = kstrtoul(buf, 0, &val);
> > +	if (err)
> > +		return err;
> >  
> > -	err = counter->ops->count_write(counter, count, &val);
> > +	err = counter->ops->count_write(counter, count, val);
> >  	if (err)
> >  		return err;
> >  
> > diff --git a/include/linux/counter.h b/include/linux/counter.h
> > index a061cdcdef7c..7e40796598a6 100644
> > --- a/include/linux/counter.h
> > +++ b/include/linux/counter.h
> > @@ -300,24 +300,6 @@ struct counter_signal_read_value {
> >  	size_t len;
> >  };
> >  
> > -/**
> > - * struct counter_count_read_value - Opaque Count read value
> > - * @buf:	string representation of Count read value
> > - * @len:	length of string in @buf
> > - */
> > -struct counter_count_read_value {
> > -	char *buf;
> > -	size_t len;
> > -};
> > -
> > -/**
> > - * struct counter_count_write_value - Opaque Count write value
> > - * @buf:	string representation of Count write value
> > - */
> > -struct counter_count_write_value {
> > -	const char *buf;
> > -};
> > -
> >  /**
> >   * struct counter_ops - Callbacks from driver
> >   * @signal_read:	optional read callback for Signal attribute. The read
> > @@ -328,15 +310,10 @@ struct counter_count_write_value {
> >   *			signal_read callback.
> >   * @count_read:		optional read callback for Count attribute. The read
> >   *			value of the respective Count should be passed back via
> > - *			the val parameter. val points to an opaque type which
> > - *			should be set only by calling the
> > - *			counter_count_read_value_set function from within the
> > - *			count_read callback.
> > + *			the val parameter.
> >   * @count_write:	optional write callback for Count attribute. The write
> >   *			value for the respective Count is passed in via the val
> > - *			parameter. val points to an opaque type which should be
> > - *			accessed only by calling the
> > - *			counter_count_write_value_get function.
> > + *			parameter.
> >   * @function_get:	function to get the current count function mode. Returns
> >   *			0 on success and negative error code on error. The index
> >   *			of the respective Count's returned function mode should
> > @@ -357,11 +334,9 @@ struct counter_ops {
> >  			   struct counter_signal *signal,
> >  			   struct counter_signal_read_value *val);
> >  	int (*count_read)(struct counter_device *counter,
> > -			  struct counter_count *count,
> > -			  struct counter_count_read_value *val);
> > +			  struct counter_count *count, unsigned long *val);
> >  	int (*count_write)(struct counter_device *counter,
> > -			   struct counter_count *count,
> > -			   struct counter_count_write_value *val);
> > +			   struct counter_count *count, unsigned long val);
> >  	int (*function_get)(struct counter_device *counter,
> >  			    struct counter_count *count, size_t *function);
> >  	int (*function_set)(struct counter_device *counter,
> > @@ -486,19 +461,9 @@ enum counter_signal_value_type {
> >  	COUNTER_SIGNAL_LEVEL = 0
> >  };
> >  
> > -enum counter_count_value_type {
> > -	COUNTER_COUNT_POSITION = 0,
> > -};
> > -
> >  void counter_signal_read_value_set(struct counter_signal_read_value *const val,
> >  				   const enum counter_signal_value_type type,
> >  				   void *const data);
> > -void counter_count_read_value_set(struct counter_count_read_value *const val,
> > -				  const enum counter_count_value_type type,
> > -				  void *const data);
> > -int counter_count_write_value_get(void *const data,
> > -				  const enum counter_count_value_type type,
> > -				  const struct counter_count_write_value *const val);
> >  
> >  int counter_register(struct counter_device *const counter);
> >  void counter_unregister(struct counter_device *const counter);  
> 

Re: [RFC 1/4] counter: Simplify the count_read and count_write callbacks

[William Breathitt Gray]

On Sun, Sep 15, 2019 at 02:47:00PM +0100, Jonathan Cameron wrote:
> On Sun, 15 Sep 2019 14:39:17 +0100
> Jonathan Cameron <jic23@jic23.retrosnub.co.uk> wrote:
> 
> > On Sun, 15 Sep 2019 14:57:56 +0900
> > William Breathitt Gray <vilhelm.gray@gmail.com> wrote:
> > 
> > > The count_read and count_write callbacks are simplified to pass val as
> > > unsigned long rather than as an opaque data structure. The opaque
> > > counter_count_read_value and counter_count_write_value structures,
> > > counter_count_value_type enum, and relevant counter_count_read_value_set
> > > and counter_count_write_value_get functions, are removed as they are no
> > > longer used.
> > > 
> > > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>  
> > 
> > Seems like a sensible bit of excessive abstraction removal to me.  I'm not
> > totally sure why these got so complex in the first place though.
> Ah. I should have read the cover letter rather than just diving in the code :)
> All explained there I see.
> 
> > 
> > Can you recall the reason as it might help to judge why we no longer
> > think the same?
> > 
> > Thanks,
> > 
> > Jonathan

The cover letter probably explains it well enough, but it may be good
anyway for posterity to add on a bit about the origins of the opaque
structures.

If I recall correctly, it was from early on when I had a dedicated set
of functions for "quadrature counters" as opposed to "simple counters"
-- eventually we abandoned that design and decided instead to keep the
interface simple since devices could be represented robustly enough with
just the core Count, Signal, and Synapse components.

I decided to keep the opaque structures anyway in the hope that they
could be used in the future to restrict the attributes exposed to a
certain set of "counter types" defined for the Counter subsystems; i.e.
"position" counters would only expose spatial coordinates, "tally"
counters would expose tally units, etc.

However, I've come to realized that this type of organization is best
left to the userspace application and that the kernelspace code should
instead be focused on maintaining a simple and robust interface for
representing the core concept of a "counter" device.

William Breathitt Gray