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

Mauro Carvalho Chehab
2010-03-26T14:41:26Z

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.

> 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.

>
> ioctl's to set/get keycodes for ir should also take a flag parameter in
> the struct to allow special properties to be set/returned for a given
> keycode mapping (I'm thinking of keycodes which powers on the computer
> for instance, that should be exposed to userspace somehow).
>
> With all of that, the struct might need to be something like:
>
> struct keycode_table_entry {
> unsigned keycode; /* e.g. KEY_A */
> unsigned table; /* Table index, for multiple keytables */
> unsigned index; /* Index in the given keytable */
> unsigned flags; /* For additional functionality */
> unsigned len; /* Of the struct */
> char scancode[]; /* Per-protocol scancode data follows */
> };
>

I don't see the need for a table index. If we have 3 input event interfaces
for a given IR, each will have its own private keycode table.

> Finally, I think irrcv should create a chardev of its own with ioctl's
> like EVIOCLEARKEYCODEBIG (and RX/TX parameter setting ioctl's). The
> same chardev can be used for IR blasting (by writing data to it once TX
> parameters have been set).

There are several different things mixed above. It may be a good idea
to allow extending the ioctls from the input event device to other input
classes. Yet, I'm currently not seeing any usage for it.

In the specific case of EVIOCGKEYCODEBIG/EVIOCSKEYCODEBIG, those are needed
for all input devices whose scancode is bigger than 32 bits. It is not
specific to IR.

I don't think we need to add ioctl's to change RX/TX parameters. The better
is to do it via sysfs. I've added yesterday one of such parameter for the
nec IR decoder, allowing enabling/disabling the decoder, per irrcv:

http://git.linuxtv.org/mchehab/ir.git?a=commit;h=b763c070b038cfd7cc5f7f7109039f5d9f995c46

When porting the RC-5 decoder from saa7134, two additional parameters will be
needed, in order to preserve the current features.

The IR tx is a different thing. It should be implemented as a separate device.

--

Cheers,
Mauro