Re: [PATCH v2] HID: core: check whether usage page item is after usage id item

From: Nicolas Saenz Julienne
Date: Wed Oct 09 2019 - 13:01:55 EST

On Wed, 2019-10-09 at 20:53 +0800, Candle Sun wrote:
> From: Candle Sun <candle.sun@xxxxxxxxxx>
>
> Upstream commit 58e75155009c ("HID: core: move Usage Page concatenation
> to Main item") adds support for Usage Page item after Usage ID items
> (such as keyboards manufactured by Primax).
>
> Usage Page concatenation in Main item works well for following report
> descriptor patterns:
>
> USAGE_PAGE (Keyboard) 05 07
> USAGE_MINIMUM (Keyboard LeftControl) 19 E0
> USAGE_MAXIMUM (Keyboard Right GUI) 29 E7
> LOGICAL_MINIMUM (0) 15 00
> LOGICAL_MAXIMUM (1) 25 01
> REPORT_SIZE (1) 75 01
> REPORT_COUNT (8) 95 08
> INPUT (Data,Var,Abs) 81 02
>
> -------------
>
> USAGE_MINIMUM (Keyboard LeftControl) 19 E0
> USAGE_MAXIMUM (Keyboard Right GUI) 29 E7
> LOGICAL_MINIMUM (0) 15 00
> LOGICAL_MAXIMUM (1) 25 01
> REPORT_SIZE (1) 75 01
> REPORT_COUNT (8) 95 08
> USAGE_PAGE (Keyboard) 05 07
> INPUT (Data,Var,Abs) 81 02
>
> But it makes the parser act wrong for the following report
> descriptor pattern(such as some Gamepads):
>
> USAGE_PAGE (Button) 05 09
> USAGE (Button 1) 09 01
> USAGE (Button 2) 09 02
> USAGE (Button 4) 09 04
> USAGE (Button 5) 09 05
> USAGE (Button 7) 09 07
> USAGE (Button 8) 09 08
> USAGE (Button 14) 09 0E
> USAGE (Button 15) 09 0F
> USAGE (Button 13) 09 0D
> USAGE_PAGE (Consumer Devices) 05 0C
> USAGE (Back) 0a 24 02
> USAGE (HomePage) 0a 23 02
> LOGICAL_MINIMUM (0) 15 00
> LOGICAL_MAXIMUM (1) 25 01
> REPORT_SIZE (1) 75 01
> REPORT_COUNT (11) 95 0B
> INPUT (Data,Var,Abs) 81 02
>
> With Usage Page concatenation in Main item, parser recognizes all the
> 11 Usages as consumer keys, it is not the HID device's real intention.
>
> This patch adds usage_page_last to flag whether Usage Page is after
> Usage ID items. usage_page_last is false default, it is set as true
> once Usage Page item is encountered and is reverted by next Usage ID
> item.
>
> Usage Page concatenation on the currently defined Usage Page will do
> firstly in Local parsing when Usage ID items encountered.
>
> When Main item is parsing, concatenation will do again with last
> defined Usage Page if usage_page_last flag is true.

Functionally I think this is the right approach. Sadly I don't have access to
any Primax device anymore so I can't test it. But I suggest you update
hid-tools' parser and add a new unit test to verify we aren't missing anything.

You can base your code on this:

https://gitlab.freedesktop.org/libevdev/hid-tools/merge_requests/37/commits

> Signed-off-by: Candle Sun <candle.sun@xxxxxxxxxx>
> Signed-off-by: Nianfu Bai <nianfu.bai@xxxxxxxxxx>
> ---
> Changes in v2:
> - Update patch title
> - Add GET_COMPLETE_USAGE macro
> - Change the logic of checking whether to concatenate usage page again
> in main parsing
> ---
> drivers/hid/hid-core.c | 31 +++++++++++++++++++++++++------
> include/linux/hid.h | 1 +
> 2 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 3eaee2c..3394222 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -35,6 +35,8 @@
>
> #include "hid-ids.h"
>
> +#define GET_COMPLETE_USAGE(page, id) (((page) << 16) + ((id) & 0xffff))

Not sure I like the macro. I'd rather have the explicit code. That said, lets
see what Benjamin has to say.

> +
> /*
> * Version Information
> */
> @@ -221,7 +223,15 @@ static int hid_add_usage(struct hid_parser *parser,
> unsigned usage, u8 size)
> hid_err(parser->device, "usage index exceeded\n");
> return -1;
> }
> - parser->local.usage[parser->local.usage_index] = usage;
> +
> + if (size <= 2) {
> + parser->local.usage_page_last = false;
> + parser->local.usage[parser->local.usage_index] =
> + GET_COMPLETE_USAGE(parser->global.usage_page, usage);
> + } else {
> + 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 ?
> @@ -366,6 +376,7 @@ static int hid_parser_global(struct hid_parser *parser,
> struct hid_item *item)
>
> case HID_GLOBAL_ITEM_TAG_USAGE_PAGE:
> parser->global.usage_page = item_udata(item);
> + parser->local.usage_page_last = true;
> return 0;
>
> case HID_GLOBAL_ITEM_TAG_LOGICAL_MINIMUM:
> @@ -543,13 +554,21 @@ static int hid_parser_local(struct hid_parser *parser,
> struct hid_item *item)
> * usage value."
> */

I'd expand the comment above to further explain what we're doing here.

>
> -static void hid_concatenate_usage_page(struct hid_parser *parser)
> +static void hid_concatenate_last_usage_page(struct hid_parser *parser)
> {
> int i;
> + unsigned int usage;
> + unsigned int usage_page = parser->global.usage_page;
> +
> + if (!parser->local.usage_page_last)
> + return;
>
> for (i = 0; i < parser->local.usage_index; i++)

Technically correct but it's preferred if you use braces here.

> - if (parser->local.usage_size[i] <= 2)
> - parser->local.usage[i] += parser->global.usage_page <<
> 16;
> + if (parser->local.usage_size[i] <= 2) {
> + usage = parser->local.usage[i];
> + parser->local.usage[i] =
> + GET_COMPLETE_USAGE(usage_page, usage);
> + }
> }
>
> /*
> @@ -561,7 +580,7 @@ static int hid_parser_main(struct hid_parser *parser,
> struct hid_item *item)
> __u32 data;
> int ret;
>
> - hid_concatenate_usage_page(parser);
> + hid_concatenate_last_usage_page(parser);
>
> data = item_udata(item);
>
> @@ -772,7 +791,7 @@ static int hid_scan_main(struct hid_parser *parser, struct
> hid_item *item)
> __u32 data;
> int i;
>
> - hid_concatenate_usage_page(parser);
> + hid_concatenate_last_usage_page(parser);
>
> data = item_udata(item);
>
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index cd41f20..2e0ea2f7 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -412,6 +412,7 @@ struct hid_local {
> unsigned usage_minimum;
> unsigned delimiter_depth;
> unsigned delimiter_branch;
> + bool usage_page_last; /* whether usage page is after usage id */
> };
>
> /*

Regards,
Nicolas

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