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    SubjectRe: [RFC] What are the goals for the architecture of an in-kernel IR system?
    On Fri, Mar 26, 2010 at 1:22 PM, Mauro Carvalho Chehab
    <> wrote:
    > Dmitry Torokhov wrote:
    >> 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.
    > Ok. I'll prepare the patches for adding the new ioctl, in a way that it will
    > also handle the legacy methods, and post for review.
    >>>> 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.
    > This don't solve the issue about how to signalize to kernel that more than one
    > input device is needed.
    > As the userspace will request the creation of those keymaps, we need some way
    > to receive such requests from userspace.
    > I can see a few ways for doing it:
    > 1) create a control device for the irrcv device as a hole,
    > that would handle such requests via ioctl (/dev/irctl[0-9]* ?)
    > 2) create a read/write sysfs node that would indicate the number of event/keymaps
    > associated with a given IR. By writing a bigger number, it would create new devices.
    > By writing a smaller number, it will delete some maps. There's an issue though:
    > what criteria would be used to delete? The newly created ones?

    This is normally handled a sysfs node on the core, something like
    'adddev'. You echo '1' to this node and a new interface is created.

    Each interface has a sysfs node, make a 'remove' attribute in it. Echo
    '1' to remove to make it disappear.

    You have to implement the code behind these interfaces but this
    convention is used in other subsubsystems.

    BTW - you're recreating everything the configfs interface did. it
    achieved the same results with mkdir/rmdir. I liked the configfs
    scheme since there are no obscure commands to learn. Everybody can
    make files and directories.

    > 3) create a fixed number of event devices, and add a sysfs attribute to enable
    > or disable it;
    > 4) create a fixed number of sysfs attributes to represent the keymaps. For example:
    > /sys/class/irrcv/irrcv0/keymap0/enabled
    >        ...
    > /sys/class/irrcv/irrcv0/keymap7/enabled
    > The input/event node will be created only when the enabled=1.
    > I don't like (2) or (3), because removing a table with (2) may end by removing the wrong
    > table, and (3) will create more event interfaces than probably needed by the majority
    > of IR users.
    > maybe (4) is the better one.
    > --
    > Cheers,
    > Mauro

    Jon Smirl
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