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

From: Nicolas Saenz Julienne
Date: Mon Mar 25 2019 - 11:12:14 EST

Hi Benjamin, Thanks for the review!

On Mon, 2019-03-25 at 16:08 +0100, Benjamin Tissoires wrote:
> 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.

Ok, I'll look into it and send a follow-up.

> 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
> > >

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