Re: [PATCH v2 1/3] HID: Use hid_parser for pre-scanning the report descriptors

[Benjamin Tissoires]

Hi Henrik,

On Wed, Aug 21, 2013 at 8:15 PM, Henrik Rydberg <rydberg@xxxxxxxxxxx> wrote:
> 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...'
>

Sure. Will change in v3.

>>
>> 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@xxxxxxxxxx>
>> ---
>>
>> 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.

oops, forgot to remove it :)

Cheers,
Benjamin

>
>> +     }
>> +
>> +     /* 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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