Re: [PATCH] HID: core: move Usage Page concatenation to hid_parser_main()

[Benjamin Tissoires]

On Mon, Mar 25, 2019 at 11:39 AM Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxxx> wrote:
>
> Hi Nicolas,
>
> On Tue, Mar 12, 2019 at 10:37 AM Nicolas Saenz Julienne
> <nsaenzjulienne@xxxxxxx> wrote:
> >
> > As seen on some USB wireless keyboards manufactured by Primax, the HID
> > parser was using some assumptions that are not always true. In this case
> > it's s the fact that, inside the scope of a main item, an Usage Page
> > will always precede an Usage.
> >
> > The spec is not pretty clear as 6.2.2.7 states "Any usage that follows
> > is interpreted as a Usage ID and concatenated with the Usage Page".
> > While 6.2.2.8 states "When the parser encounters a main item it
> > concatenates the last declared Usage Page with a Usage to form a
> > complete usage value." Being somewhat contradictory it was decided to
> > match Window's implementation, which follows 6.2.2.8.
> >
> > In summary, the patch moves the Usage Page concatenation from the local
> > item parsing function to the main item parsing function.
> >
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> > ---
>
> Patch looks good to me.
>
> Terry, did you have time to review it?
>
> Cheers,
> Benjamin
>
> >
> > Note: A PR in hid-tools shoud show up anytime soon
> >
> >  drivers/hid/hid-core.c | 30 ++++++++++++++++++------------
> >  include/linux/hid.h    |  1 +
> >  2 files changed, 19 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> > index 9993b692598f..158468ef23a6 100644
> > --- a/drivers/hid/hid-core.c
> > +++ b/drivers/hid/hid-core.c
> > @@ -218,13 +218,14 @@ static unsigned hid_lookup_collection(struct hid_parser *parser, unsigned type)
> >   * Add a usage to the temporary parser table.
> >   */
> >
> > -static int hid_add_usage(struct hid_parser *parser, unsigned usage)
> > +static int hid_add_usage(struct hid_parser *parser, unsigned usage, __u8 size)
> >  {
> >         if (parser->local.usage_index >= HID_MAX_USAGES) {
> >                 hid_err(parser->device, "usage index exceeded\n");
> >                 return -1;
> >         }
> >         parser->local.usage[parser->local.usage_index] = usage;
> > +       parser->local.usage_size[parser->local.usage_index] = size;
> >         parser->local.collection_index[parser->local.usage_index] =
> >                 parser->collection_stack_ptr ?
> >                 parser->collection_stack[parser->collection_stack_ptr - 1] : 0;
> > @@ -486,10 +487,7 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
> >                         return 0;
> >                 }
> >
> > -               if (item->size <= 2)
> > -                       data = (parser->global.usage_page << 16) + data;
> > -
> > -               return hid_add_usage(parser, data);
> > +               return hid_add_usage(parser, data, item->size);
> >
> >         case HID_LOCAL_ITEM_TAG_USAGE_MINIMUM:
> >
> > @@ -498,9 +496,6 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
> >                         return 0;
> >                 }
> >
> > -               if (item->size <= 2)
> > -                       data = (parser->global.usage_page << 16) + data;
> > -
> >                 parser->local.usage_minimum = data;
> >                 return 0;
> >
> > @@ -511,9 +506,6 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
> >                         return 0;
> >                 }
> >
> > -               if (item->size <= 2)
> > -                       data = (parser->global.usage_page << 16) + data;
> > -
> >                 count = data - parser->local.usage_minimum;
> >                 if (count + parser->local.usage_index >= HID_MAX_USAGES) {
> >                         /*
> > @@ -533,7 +525,7 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
> >                 }
> >
> >                 for (n = parser->local.usage_minimum; n <= data; n++)
> > -                       if (hid_add_usage(parser, n)) {
> > +                       if (hid_add_usage(parser, n, item->size)) {
> >                                 dbg_hid("hid_add_usage failed\n");
> >                                 return -1;
> >                         }
> > @@ -553,8 +545,22 @@ static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
> >
> >  static int hid_parser_main(struct hid_parser *parser, struct hid_item *item)
> >  {
> > +       unsigned int usages;
> >         __u32 data;
> >         int ret;
> > +       int i;
> > +
> > +       usages = max_t(unsigned, parser->local.usage_index,
> > +                                parser->global.report_count);
> > +
> > +       /*
> > +        * As per specification, 6.2.2.8:
> > +        * "When the parser encounters a main item it concatenates the last
> > +        * declared Usage Page with a Usage to form a complete usage value."
> > +        */
> > +       for (i = 0; i < usages; i++)
> > +               if (parser->local.usage_size[i] <= 2)
> > +                       parser->local.usage[i] += parser->global.usage_page << 16;

Actually, the good thing of having a test suite, is that it raises bugs :)

You are also missing the computation of the usage in hid_scan_main().
This makes the autoloading of hid-multitouch fail, and thus the test
suite failing.

Cheers,
Benjamin

> >
> >         data = item_udata(item);
> >
> > diff --git a/include/linux/hid.h b/include/linux/hid.h
> > index f9707d1dcb58..d1fb4b678873 100644
> > --- a/include/linux/hid.h
> > +++ b/include/linux/hid.h
> > @@ -417,6 +417,7 @@ struct hid_global {
> >
> >  struct hid_local {
> >         unsigned usage[HID_MAX_USAGES]; /* usage array */
> > +       __u8 usage_size[HID_MAX_USAGES]; /* usage size array */
> >         unsigned collection_index[HID_MAX_USAGES]; /* collection index array */
> >         unsigned usage_index;
> >         unsigned usage_minimum;
> > --
> > 2.21.0
> >