Re: [RFC] What are the goals for the architecture of an in-kernel IR system?

Dmitry Torokhov
2010-03-26T16:02:02Z

On Fri, Mar 26, 2010 at 11:40:41AM -0300, Mauro Carvalho Chehab wrote:
> David Härdeman wrote:
> > On Thu, Mar 25, 2010 at 11:42:33AM -0300, Mauro Carvalho Chehab wrote:
> >>> 10) extend keycode table replacement to support big/variable
> >>> sized scancodes;
> >> Pending.
> >>
> >> The current limit here is the scancode ioctl's are defined as:
> >>
> >> #define EVIOCGKEYCODE _IOR('E', 0x04, int[2]) /* get keycode */
> >> #define EVIOCSKEYCODE _IOW('E', 0x04, int[2]) /* set keycode */
> >>
> >> As int size is 32 bits, and we must pass both 64 (or even bigger) scancodes, associated
> >> with a keycode, there's not enough bits there for IR.
> >>
> >> The better approach seems to create an struct with an arbitrary long size, like:
> >>
> >> struct keycode_table_entry {
> >> unsigned keycode;
> >> char scancode[32]; /* 32 is just an arbitrary long array - maybe shorter */
> >> int len;
> >> }
> >>
> >> and re-define the ioctls. For example we might be doing:
> >>
> >> #define EVIOCGKEYCODEBIG _IOR('E', 0x04, struct keycode_table_entry)
> >> #define EVIOCSKEYCODEBIG _IOW('E', 0x04, struct keycode_table_entry)
> >> #define EVIOCLEARKEYCODEBIG _IOR('E', 0x04, void)
> >>
> >> Provided that the size for struct keycode_table_entry is different, _IO will generate
> >> a different magic number for those.
> >>
> >> Or, instead of using 0x04, just use another sequential number at the 'E' namespace.
> >>
> >> An specific function to clear the table is needed with big scancode space,
> >> as already discussed.
> >>
> >
> > I'd suggest:
> >
> > struct keycode_table_entry {
> > unsigned keycode;
> > unsigned index;
> > unsigned len;
> > char scancode[];
> > };
> >
> > Use index in EVIOCGKEYCODEBIG to look up a keycode (all other fields are
> > ignored), that way no special function to clear the table is necessary,
> > instead you do a loop with:
> >
> > EVIOCGKEYCODEBIG (with index 0)
> > EVIOCSKEYCODEBIG (with the returned struct from EVIOCGKEYCODEBIG and
> > keycode = KEY_RESERVED)
> >
> > until EVIOCGKEYCODEBIG returns an error.
>
> Makes sense.

Yes, I think so too. Just need a nice way to handle transition, I'd
like in the end to have drivers implement only the improved methods and
map legacy methods in evdev.

>
> > This also allows you to get all the current mappings from the kernel
> > without having to blindly search through an arbitrarily large keyspace.
> >
> > Also, EVIOCLEARKEYCODEBIG should be:
> >
> > #define EVIOCLEARKEYCODEBIG _IOR('E', 0x04, struct keycode_table_entry)
> >
> > That way a user space application can simply call EVIOCLEARKEYCODEBIG,
> > ask the user for an appropriate keycode, fill in the keycode member of
> > the struct returned from EVIOCLEARKEYCODEBIG and call EVIOCSKEYCODEBIG.
>
> By using the index concept, I don't think we need another ioctl. Also,
> there's no way for kernel to handle it, as it will be using the same
> magic number of EVIOCGKEYCODEBIG.
>
> > On a related note, I really think the interface would benefit from
> > allowing more than one keytable per irrcv device with an input device
> > created per keytable. That way you can have one input device per remote
> > control. This implies that EVIOCLEARKEYCODEBIG is a bit misplaced as an
> > evdev IOCTL since there's an N-1 mapping between input devices and irrcv
> > devices.
>
> I don't think that an ioctl over one /dev/input/event should be the proper way
> to ask kernel to create another filtered /dev/input/event. As it were commented
> that the multimedia keys on some keyboards could benefit on having a filter
> capability, maybe we may have a sysfs node at class input that would allow
> the creation/removal of the filtered event interface.

No, if you want separate event devices just create a new instance of
input device for every keymap and have driver/irrcv class route events
to proper input device.

Thanks.

--
Dmitry