On Fri, May 29, 2020 at 03:26:04PM +0200, Pavel Machek wrote: > On Sat 2020-05-16 15:20:02, William Breathitt Gray wrote: > > This patch adds high-level documentation about the Counter subsystem > > character device interface. > > > > Signed-off-by: William Breathitt Gray <vilhelm.g...@gmail.com> > > --- > > Documentation/driver-api/generic-counter.rst | 112 +++++++++++++------ > > 1 file changed, 76 insertions(+), 36 deletions(-) > > > > diff --git a/Documentation/driver-api/generic-counter.rst > > b/Documentation/driver-api/generic-counter.rst > > index 8f85c30dea0b..58045b33b576 100644 > > --- a/Documentation/driver-api/generic-counter.rst > > +++ b/Documentation/driver-api/generic-counter.rst > > > + > > +Counter chrdev > > +-------------- > > +Translates counter data to the standard Counter character device; data > > +is transferred via standard character device read/write calls. > > + > > +Sysfs Interface > > +=============== > > + > > +Several sysfs attributes are generated by the Generic Counter interface, > > +and reside under the `/sys/bus/counter/devices/counterX` directory, > > +where `X` is to the respective counter device id. Please see > > +Documentation/ABI/testing/sysfs-bus-counter for detailed information on > > +each Generic Counter interface sysfs attribute. > > + > > +Through these sysfs attributes, programs and scripts may interact with > > +the Generic Counter paradigm Counts, Signals, and Synapses of respective > > +counter devices. > > + > > +Counter Character Device > > +======================== > > + > > +Counter character device nodes are created under the `/dev` directory as > > +`counterX`, where `X` is the respective counter device id. Defines for > > +the standard Counter data types are exposed via the userspace > > +`include/uapi/linux/counter-types.h` file. > > + > > +The first 196095 bytes of the character device serve as a control > > +selection area where control exposure of desired Counter components and > > +extensions may be selected. Each byte serves as a boolean selection > > +indicator for a respective Counter component or extension. The format of > > +this area is as follows: > > + > > +* For each device extension, a byte is required. > > +* For each Signal, a byte is reserved for the Signal component, and a > > + byte is reserved for each Signal extension. > > +* For each Count, a byte is reserved for the Count component, a byte is > > + reserved for the count function, a byte is reserved for each Synapse > > + action, and byte is reserved for each Count extension. > > + > > +The selected Counter components and extensions may then be interfaced > > +after the first 196095 bytes via standard character device read/write > > +operations. The number of bytes available for each component or > > +extension is dependent on their respective data type: u8 will have 1 > > +byte available, u64 will have 8 bytes available, strings will have 64 > > +bytes available, etc. > > This looks like very, very strange interface, and not described in detail > required to understand it. > > Could you take a look at input subsystem, /dev/input/event0? Perhaps it is > directly usable, and if not something similar should probably be acceptable. > > Best regards, > Pavel
Yes, I don't think this is a good interface afterall. I'm implementing a different design for v3 that should be more intuitive. The input subsystem could be useful for streams of events such as timestamps, so I'll take a look at it as well in case something similar to it could be used. William Breathitt Gray
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