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Date: Wed, 21 Aug 2013 20:15:55 +0200
From: Henrik Rydberg <rydberg@...omail.se>
To: Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc: Benjamin Tissoires <benjamin.tissoires@...il.com>,
Jiri Kosina <jkosina@...e.cz>,
Stephane Chatty <chatty@...c.fr>,
Alexander Holler <holler@...oftware.de>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] HID: Use hid_parser for pre-scanning the report
descriptors
Hi Benjamin,
this looks pretty good to me, just a few nitpicks below.
> hid_scan_report() implements its own HID report descriptor parsing. It is
> going to be really bad with the detection of Win 8 certified touchscreen,
> as this detection relies on a special feature and on the report_size and
> report_count fields.
How about 'The Win 8 detection is sufficiently complex to warrant use
of the full parser code, in spite of the inferred memory
usage. Therefore...'
>
> We can use the existing HID parser in hid-core for hid_scan_report()
> by re-using the code from hid_open_report(). hid_parser_global,
> hid_parser_local and hid_parser_reserved does not have any side effects.
> We just need to reimplement the MAIN_ITEM callback to have a proper
> parsing without side effects.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> ---
>
> changes in v2:
> - moved "flags" processing in patch 2/3 (so use hid->group in this patch)
> - hid_scan_report() is less verbose when errors are found in the descriptor
> - hid_scan_report() is tolerant to parsing errors
> - fixed usage_page handling in hid_scan_collection(), which fixes sensors detection
> - amended commit message
>
> drivers/hid/hid-core.c | 106 +++++++++++++++++++++++++++++++------------------
> 1 file changed, 67 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 3efe19f..e072b15 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -677,12 +677,55 @@ static u8 *fetch_item(__u8 *start, __u8 *end, struct hid_item *item)
> return NULL;
> }
>
> -static void hid_scan_usage(struct hid_device *hid, u32 usage)
> +static void hid_scan_input_usage(struct hid_parser *parser, u32 usage)
> {
> + struct hid_device *hid = parser->device;
> +
> if (usage == HID_DG_CONTACTID)
> hid->group = HID_GROUP_MULTITOUCH;
> }
>
> +static void hid_scan_collection(struct hid_parser *parser, unsigned type)
> +{
> + struct hid_device *hid = parser->device;
> +
> + if (((parser->global.usage_page << 16) == HID_UP_SENSOR) &&
> + type == HID_COLLECTION_PHYSICAL)
> + hid->group = HID_GROUP_SENSOR_HUB;
> +}
> +
> +static int hid_scan_main(struct hid_parser *parser, struct hid_item *item)
> +{
> + __u32 data;
> + int i;
> +
> + data = item_udata(item);
> +
> + switch (item->tag) {
> + case HID_MAIN_ITEM_TAG_BEGIN_COLLECTION:
> + hid_scan_collection(parser, data & 0xff);
> + break;
> + case HID_MAIN_ITEM_TAG_END_COLLECTION:
> + break;
> + case HID_MAIN_ITEM_TAG_INPUT:
> + for (i = 0; i < parser->local.usage_index; i++)
> + hid_scan_input_usage(parser, parser->local.usage[i]);
> + break;
> + case HID_MAIN_ITEM_TAG_OUTPUT:
> + break;
> + case HID_MAIN_ITEM_TAG_FEATURE:
> + break;
> + default:
> + hid_err(parser->device, "unknown main item tag 0x%x\n",
> + item->tag);
Looks this this message is a duplicate as well.
> + }
> +
> + /* Reset the local parser environment */
> + memset(&parser->local, 0, sizeof(parser->local));
> +
> + return 0;
> +}
> +
> /*
> * Scan a report descriptor before the device is added to the bus.
> * Sets device groups and other properties that determine what driver
> @@ -690,48 +733,33 @@ static void hid_scan_usage(struct hid_device *hid, u32 usage)
> */
> static int hid_scan_report(struct hid_device *hid)
> {
> - unsigned int page = 0, delim = 0;
> + struct hid_parser *parser;
> + struct hid_item item;
> __u8 *start = hid->dev_rdesc;
> __u8 *end = start + hid->dev_rsize;
> - unsigned int u, u_min = 0, u_max = 0;
> - struct hid_item item;
> + static int (*dispatch_type[])(struct hid_parser *parser,
> + struct hid_item *item) = {
> + hid_scan_main,
> + hid_parser_global,
> + hid_parser_local,
> + hid_parser_reserved
> + };
>
> - hid->group = HID_GROUP_GENERIC;
> - while ((start = fetch_item(start, end, &item)) != NULL) {
> - if (item.format != HID_ITEM_FORMAT_SHORT)
> - return -EINVAL;
> - if (item.type == HID_ITEM_TYPE_GLOBAL) {
> - if (item.tag == HID_GLOBAL_ITEM_TAG_USAGE_PAGE)
> - page = item_udata(&item) << 16;
> - } else if (item.type == HID_ITEM_TYPE_LOCAL) {
> - if (delim > 1)
> - break;
> - u = item_udata(&item);
> - if (item.size <= 2)
> - u += page;
> - switch (item.tag) {
> - case HID_LOCAL_ITEM_TAG_DELIMITER:
> - delim += !!u;
> - break;
> - case HID_LOCAL_ITEM_TAG_USAGE:
> - hid_scan_usage(hid, u);
> - break;
> - case HID_LOCAL_ITEM_TAG_USAGE_MINIMUM:
> - u_min = u;
> - break;
> - case HID_LOCAL_ITEM_TAG_USAGE_MAXIMUM:
> - u_max = u;
> - for (u = u_min; u <= u_max; u++)
> - hid_scan_usage(hid, u);
> - break;
> - }
> - } else if (page == HID_UP_SENSOR &&
> - item.type == HID_ITEM_TYPE_MAIN &&
> - item.tag == HID_MAIN_ITEM_TAG_BEGIN_COLLECTION &&
> - (item_udata(&item) & 0xff) == HID_COLLECTION_PHYSICAL)
> - hid->group = HID_GROUP_SENSOR_HUB;
> - }
> + parser = vzalloc(sizeof(struct hid_parser));
> + if (!parser)
> + return -ENOMEM;
> +
> + parser->device = hid;
> +
> + /*
> + * The parsing is simpler than the one in hid_open_report() as we should
> + * be robust against hid errors. Those errors will be raised by
> + * hid_open_report() anyway.
> + */
> + while ((start = fetch_item(start, end, &item)) != NULL)
> + dispatch_type[item.type](parser, &item);
>
> + vfree(parser);
> return 0;
> }
>
> --
> 1.8.3.1
>
Thanks,
Henrik
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