| Message ID | 2a8d7fe2e0ea435e19c89ba2aff15218c7b6eb91.1589654470.git.vilhelm.gray@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Introduce the Counter character device interface | expand |
On Sat, 16 May 2020 15:20:00 -0400 William Breathitt Gray <vilhelm.gray@gmail.com> wrote: > The Counter subsystem architecture and driver implementations have > changed in order to handle Counter sysfs interactions in a more > consistent way. This patch updates the Generic Counter interface > documentation to reflect the changes. > > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com> Looks good to me. Jonathan > --- > Documentation/driver-api/generic-counter.rst | 215 +++++++++++++------ > 1 file changed, 149 insertions(+), 66 deletions(-) > > diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst > index e622f8f6e56a..8f85c30dea0b 100644 > --- a/Documentation/driver-api/generic-counter.rst > +++ b/Documentation/driver-api/generic-counter.rst > @@ -250,8 +250,8 @@ for defining a counter device. > .. kernel-doc:: drivers/counter/counter.c > :export: > > -Implementation > -============== > +Driver Implementation > +===================== > > To support a counter device, a driver must first allocate the available > Counter Signals via counter_signal structures. These Signals should > @@ -267,25 +267,58 @@ respective counter_count structure. These counter_count structures are > set to the counts array member of an allocated counter_device structure > before the Counter is registered to the system. > > -Driver callbacks should be provided to the counter_device structure via > -a constant counter_ops structure in order to communicate with the > -device: to read and write various Signals and Counts, and to set and get > -the "action mode" and "function mode" for various Synapses and Counts > -respectively. > +Driver callbacks must be provided to the counter_device structure in > +order to communicate with the device: to read and write various Signals > +and Counts, and to set and get the "action mode" and "function mode" for > +various Synapses and Counts respectively. > > A defined counter_device structure may be registered to the system by > passing it to the counter_register function, and unregistered by passing > it to the counter_unregister function. Similarly, the > -devm_counter_register and devm_counter_unregister functions may be used > -if device memory-managed registration is desired. > - > -Extension sysfs attributes can be created for auxiliary functionality > -and data by passing in defined counter_device_ext, counter_count_ext, > -and counter_signal_ext structures. In these cases, the > -counter_device_ext structure is used for global/miscellaneous exposure > -and configuration of the respective Counter device, while the > -counter_count_ext and counter_signal_ext structures allow for auxiliary > -exposure and configuration of a specific Count or Signal respectively. > +devm_counter_register function may be used if device memory-managed > +registration is desired. > + > +The struct counter_data structure is used to define counter extensions > +for Signals, Synapses, and Counts. > + > +The "type" member specifies the type of data (e.g. unsigned long, > +boolean, etc.) handled by this extension. The "read" and "write" members > +can then be set by the counter device driver with callbacks to handle > +that data. > + > +Convenience macros such as `COUNTER_DATA_COUNT_U64` are provided for use > +by driver authors. In particular, driver authors are expected to use > +the provided macros for standard Counter subsystem attributes in order > +to maintain a consistent interface for userspace. For example, a counter > +device driver may define several standard attributes like so:: > + > + struct counter_data count_ext[] = { > + COUNTER_DATA_DIRECTION(count_direction_read), > + COUNTER_DATA_ENABLE(count_enable_read, count_enable_write), > + COUNTER_DATA_CEILING(count_ceiling_read, count_ceiling_write), > + }; > + > +This makes it intuitive to see, add, and modify the attributes that are > +supported by this driver ("direction", "enable", and "ceiling") and to > +maintain this code without getting lost in a web of struct braces. > + > +Callbacks must match the function type expected for the respective > +component or extension. These function types are defined in the struct > +counter_data structure as the "`*_read`" and "`*_write`" union members. > + > +The corresponding callback prototypes for the extensions mentioned in > +the previous example above would be:: > + > + int count_direction_read(struct counter_device *counter, > + struct counter_count *count, u8 *direction); > + int count_enable_read(struct counter_device *counter, > + struct counter_count *count, u8 *enable); > + int count_enable_write(struct counter_device *counter, > + struct counter_count *count, u8 enable); > + int count_ceiling_read(struct counter_device *counter, > + struct counter_count *count, u64 *ceiling); > + int count_ceiling_write(struct counter_device *counter, > + struct counter_count *count, u64 ceiling); > > Determining the type of extension to create is a matter of scope. > > @@ -313,52 +346,102 @@ Determining the type of extension to create is a matter of scope. > chip overheated via a device extension called "error_overtemp": > /sys/bus/counter/devices/counterX/error_overtemp > > -Architecture > -============ > - > -When the Generic Counter interface counter module is loaded, the > -counter_init function is called which registers a bus_type named > -"counter" to the system. Subsequently, when the module is unloaded, the > -counter_exit function is called which unregisters the bus_type named > -"counter" from the system. > - > -Counter devices are registered to the system via the counter_register > -function, and later removed via the counter_unregister function. The > -counter_register function establishes a unique ID for the Counter > -device and creates a respective sysfs directory, where X is the > -mentioned unique ID: > - > - /sys/bus/counter/devices/counterX > - > -Sysfs attributes are created within the counterX directory to expose > -functionality, configurations, and data relating to the Counts, Signals, > -and Synapses of the Counter device, as well as options and information > -for the Counter device itself. > - > -Each Signal has a directory created to house its relevant sysfs > -attributes, where Y is the unique ID of the respective Signal: > - > - /sys/bus/counter/devices/counterX/signalY > - > -Similarly, each Count has a directory created to house its relevant > -sysfs attributes, where Y is the unique ID of the respective Count: > - > - /sys/bus/counter/devices/counterX/countY > - > -For a more detailed breakdown of the available Generic Counter interface > -sysfs attributes, please refer to the > -Documentation/ABI/testing/sysfs-bus-counter file. > - > -The Signals and Counts associated with the Counter device are registered > -to the system as well by the counter_register function. The > -signal_read/signal_write driver callbacks are associated with their > -respective Signal attributes, while the count_read/count_write and > -function_get/function_set driver callbacks are associated with their > -respective Count attributes; similarly, the same is true for the > -action_get/action_set driver callbacks and their respective Synapse > -attributes. If a driver callback is left undefined, then the respective > -read/write permission is left disabled for the relevant attributes. > - > -Similarly, extension sysfs attributes are created for the defined > -counter_device_ext, counter_count_ext, and counter_signal_ext > -structures that are passed in. > +Subsystem Architecture > +====================== > + > +Counter drivers pass and take data natively (i.e. `u8`, `u64`, `char *`, > +etc.) and the shared counter module handles the translation between the > +sysfs interface. This gurantees a standard userspace interface for all > +counter drivers, and helps generalize the Generic Counter driver ABI in > +order to support the Generic Counter chrdev interface without > +significant changes to the existing counter drivers. > + > +A high-level view of how a count value is passed down from a counter > +driver can be exemplified by the following:: > + > + Count data request: > + ~~~~~~~~~~~~~~~~~~~ > + ---------------------- > + / Counter device \ > + +----------------------+ > + | Count register: 0x28 | > + +----------------------+ > + | > + ----------------- > + / raw count data / > + ----------------- > + | > + V > + +----------------------------+ > + | Counter device driver |----------+ > + +----------------------------+ | > + | Processes data from device | ------------------- > + |----------------------------| / driver callbacks / > + | Type: unsigned long | ------------------- > + | Value: 42 | | > + +----------------------------+ | > + | | > + ---------------- | > + / unsigned long / | > + ---------------- | > + | | > + | V > + | +----------------------+ > + | | Counter core | > + | +----------------------+ > + | | Routes device driver | > + | | callbacks to the | > + | | userspace interfaces | > + | +----------------------+ > + | | > + | ------------------- > + | / driver callbacks / > + | ------------------- > + | | > + +-------+ | > + | | > + | +---------------+ > + | | > + V | > + +--------------------+ | > + | Counter sysfs |<-+ > + +--------------------+ > + | Translates to the | > + | standard Counter | > + | sysfs output | > + |--------------------| > + | Type: const char * | > + | Value: "42" | > + +--------------------+ > + | > + --------------- > + / const char * / > + --------------- > + | > + V > + +--------------------------------------------------+ > + | `/sys/bus/counter/devices/counterX/countY/count` | > + +--------------------------------------------------+ > + \ Count: "42" / > + -------------------------------------------------- > + > +There are three primary components involved: > + > +Counter device driver > +--------------------- > +Communicates with the hardware device to read/write data; e.g. counter > +drivers for quadrature encoders, timers, etc. > + > +Counter core > +------------ > +Registers the counter device driver to the system so that the respective > +callbacks are called during userspace interaction. > + > +Counter sysfs > +------------- > +Translates counter data to the standard Counter sysfs interface format > +and vice versa. > + > +Please refer to the `Documentation/ABI/testing/sysfs-bus-counter` file > +for a detailed breakdown of the available Generic Counter interface > +sysfs attributes.
diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst index e622f8f6e56a..8f85c30dea0b 100644 --- a/Documentation/driver-api/generic-counter.rst +++ b/Documentation/driver-api/generic-counter.rst @@ -250,8 +250,8 @@ for defining a counter device. .. kernel-doc:: drivers/counter/counter.c :export: -Implementation -============== +Driver Implementation +===================== To support a counter device, a driver must first allocate the available Counter Signals via counter_signal structures. These Signals should @@ -267,25 +267,58 @@ respective counter_count structure. These counter_count structures are set to the counts array member of an allocated counter_device structure before the Counter is registered to the system. -Driver callbacks should be provided to the counter_device structure via -a constant counter_ops structure in order to communicate with the -device: to read and write various Signals and Counts, and to set and get -the "action mode" and "function mode" for various Synapses and Counts -respectively. +Driver callbacks must be provided to the counter_device structure in +order to communicate with the device: to read and write various Signals +and Counts, and to set and get the "action mode" and "function mode" for +various Synapses and Counts respectively. A defined counter_device structure may be registered to the system by passing it to the counter_register function, and unregistered by passing it to the counter_unregister function. Similarly, the -devm_counter_register and devm_counter_unregister functions may be used -if device memory-managed registration is desired. - -Extension sysfs attributes can be created for auxiliary functionality -and data by passing in defined counter_device_ext, counter_count_ext, -and counter_signal_ext structures. In these cases, the -counter_device_ext structure is used for global/miscellaneous exposure -and configuration of the respective Counter device, while the -counter_count_ext and counter_signal_ext structures allow for auxiliary -exposure and configuration of a specific Count or Signal respectively. +devm_counter_register function may be used if device memory-managed +registration is desired. + +The struct counter_data structure is used to define counter extensions +for Signals, Synapses, and Counts. + +The "type" member specifies the type of data (e.g. unsigned long, +boolean, etc.) handled by this extension. The "read" and "write" members +can then be set by the counter device driver with callbacks to handle +that data. + +Convenience macros such as `COUNTER_DATA_COUNT_U64` are provided for use +by driver authors. In particular, driver authors are expected to use +the provided macros for standard Counter subsystem attributes in order +to maintain a consistent interface for userspace. For example, a counter +device driver may define several standard attributes like so:: + + struct counter_data count_ext[] = { + COUNTER_DATA_DIRECTION(count_direction_read), + COUNTER_DATA_ENABLE(count_enable_read, count_enable_write), + COUNTER_DATA_CEILING(count_ceiling_read, count_ceiling_write), + }; + +This makes it intuitive to see, add, and modify the attributes that are +supported by this driver ("direction", "enable", and "ceiling") and to +maintain this code without getting lost in a web of struct braces. + +Callbacks must match the function type expected for the respective +component or extension. These function types are defined in the struct +counter_data structure as the "`*_read`" and "`*_write`" union members. + +The corresponding callback prototypes for the extensions mentioned in +the previous example above would be:: + + int count_direction_read(struct counter_device *counter, + struct counter_count *count, u8 *direction); + int count_enable_read(struct counter_device *counter, + struct counter_count *count, u8 *enable); + int count_enable_write(struct counter_device *counter, + struct counter_count *count, u8 enable); + int count_ceiling_read(struct counter_device *counter, + struct counter_count *count, u64 *ceiling); + int count_ceiling_write(struct counter_device *counter, + struct counter_count *count, u64 ceiling); Determining the type of extension to create is a matter of scope. @@ -313,52 +346,102 @@ Determining the type of extension to create is a matter of scope. chip overheated via a device extension called "error_overtemp": /sys/bus/counter/devices/counterX/error_overtemp -Architecture -============ - -When the Generic Counter interface counter module is loaded, the -counter_init function is called which registers a bus_type named -"counter" to the system. Subsequently, when the module is unloaded, the -counter_exit function is called which unregisters the bus_type named -"counter" from the system. - -Counter devices are registered to the system via the counter_register -function, and later removed via the counter_unregister function. The -counter_register function establishes a unique ID for the Counter -device and creates a respective sysfs directory, where X is the -mentioned unique ID: - - /sys/bus/counter/devices/counterX - -Sysfs attributes are created within the counterX directory to expose -functionality, configurations, and data relating to the Counts, Signals, -and Synapses of the Counter device, as well as options and information -for the Counter device itself. - -Each Signal has a directory created to house its relevant sysfs -attributes, where Y is the unique ID of the respective Signal: - - /sys/bus/counter/devices/counterX/signalY - -Similarly, each Count has a directory created to house its relevant -sysfs attributes, where Y is the unique ID of the respective Count: - - /sys/bus/counter/devices/counterX/countY - -For a more detailed breakdown of the available Generic Counter interface -sysfs attributes, please refer to the -Documentation/ABI/testing/sysfs-bus-counter file. - -The Signals and Counts associated with the Counter device are registered -to the system as well by the counter_register function. The -signal_read/signal_write driver callbacks are associated with their -respective Signal attributes, while the count_read/count_write and -function_get/function_set driver callbacks are associated with their -respective Count attributes; similarly, the same is true for the -action_get/action_set driver callbacks and their respective Synapse -attributes. If a driver callback is left undefined, then the respective -read/write permission is left disabled for the relevant attributes. - -Similarly, extension sysfs attributes are created for the defined -counter_device_ext, counter_count_ext, and counter_signal_ext -structures that are passed in. +Subsystem Architecture +====================== + +Counter drivers pass and take data natively (i.e. `u8`, `u64`, `char *`, +etc.) and the shared counter module handles the translation between the +sysfs interface. This gurantees a standard userspace interface for all +counter drivers, and helps generalize the Generic Counter driver ABI in +order to support the Generic Counter chrdev interface without +significant changes to the existing counter drivers. + +A high-level view of how a count value is passed down from a counter +driver can be exemplified by the following:: + + Count data request: + ~~~~~~~~~~~~~~~~~~~ + ---------------------- + / Counter device \ + +----------------------+ + | Count register: 0x28 | + +----------------------+ + | + ----------------- + / raw count data / + ----------------- + | + V + +----------------------------+ + | Counter device driver |----------+ + +----------------------------+ | + | Processes data from device | ------------------- + |----------------------------| / driver callbacks / + | Type: unsigned long | ------------------- + | Value: 42 | | + +----------------------------+ | + | | + ---------------- | + / unsigned long / | + ---------------- | + | | + | V + | +----------------------+ + | | Counter core | + | +----------------------+ + | | Routes device driver | + | | callbacks to the | + | | userspace interfaces | + | +----------------------+ + | | + | ------------------- + | / driver callbacks / + | ------------------- + | | + +-------+ | + | | + | +---------------+ + | | + V | + +--------------------+ | + | Counter sysfs |<-+ + +--------------------+ + | Translates to the | + | standard Counter | + | sysfs output | + |--------------------| + | Type: const char * | + | Value: "42" | + +--------------------+ + | + --------------- + / const char * / + --------------- + | + V + +--------------------------------------------------+ + | `/sys/bus/counter/devices/counterX/countY/count` | + +--------------------------------------------------+ + \ Count: "42" / + -------------------------------------------------- + +There are three primary components involved: + +Counter device driver +--------------------- +Communicates with the hardware device to read/write data; e.g. counter +drivers for quadrature encoders, timers, etc. + +Counter core +------------ +Registers the counter device driver to the system so that the respective +callbacks are called during userspace interaction. + +Counter sysfs +------------- +Translates counter data to the standard Counter sysfs interface format +and vice versa. + +Please refer to the `Documentation/ABI/testing/sysfs-bus-counter` file +for a detailed breakdown of the available Generic Counter interface +sysfs attributes.
The Counter subsystem architecture and driver implementations have changed in order to handle Counter sysfs interactions in a more consistent way. This patch updates the Generic Counter interface documentation to reflect the changes. Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com> --- Documentation/driver-api/generic-counter.rst | 215 +++++++++++++------ 1 file changed, 149 insertions(+), 66 deletions(-)