Hi Henrik,
On 13/08/13 21:17, rydberg@xxxxxxxxxxx wrote:
> Hi Benjamin,
>
> thanks for the patches, things are looking a lot better this way.
thanks for the review :)
>
>> hid_scan_report() implements its own HID report descriptor parsing. It was
>> fine until we added the SENSOR_HUB detection. It is going to be even worse
>> 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.
>
> It was fine with sensors added as well. You seem to have found a
> reasonable way to add support for all the tags, but there is a
> rationale for the current scanner that may not have been addressed in
> this patch: it is robust against parse errors. This is particularly
> important for devices which later tweak the report, often in order to
> parse properly.
Hmm, I disagree: if a driver needs to tweak a report, then it will
register itself in hid_have_special_driver. The pre-scanning pass is
done only for devices which are not in hid_have_special_driver. So I
consider it is safe to assume that the report descriptor does not
contain errors. If it does, then it will just leave the current
hid-group state, and will just pop an debug information.
>
> Please find some further comments inline.
>
>> 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.
>>
>> Instead of directly overwriting the ->group field, this patch introduce
>> a ->flags field and then decide which group the device belongs to,
>> depending on the whole parsing (not just the local item). This will be
>> useful for Win 8 multitouch devices, which are multitouch devices and
>> Win 8 certified (so 2 flags to check).
>>
>> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
>> ---
>> drivers/hid/hid-core.c | 131 +++++++++++++++++++++++++++++++++++--------------
>> include/linux/hid.h | 4 ++
>> 2 files changed, 97 insertions(+), 38 deletions(-)
>>
>> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
>> index 3efe19f..d8cdb0a 100644
>> --- a/drivers/hid/hid-core.c
>> +++ b/drivers/hid/hid-core.c
>> @@ -677,10 +677,49 @@ 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)
>> {
>> if (usage == HID_DG_CONTACTID)
>> - hid->group = HID_GROUP_MULTITOUCH;
>> + parser->flags |= HID_FLAG_MULTITOUCH;
>
> Did you consider reusing the group flags, e.g., parser->groups |= (1
> << HID_GROUP_MULTITOUCH)? This change could be made regardless of the
> parser logic.
If nobody is against changing the values of the different groups across
kernel version (which should be harmless), then I fully agree, we can
use the group item as a bit field (but we would be able to only have 16
different device groups).
>
>> +}
>> +
>> +static void hid_scan_open_collection(struct hid_parser *parser, unsigned type)
>
> We are not really opening anything here, so perhaps
> hid_scan_collection would suffice.
Ok, will change in v2
>
>> +{
>> + if (parser->global.usage_page == HID_UP_SENSOR &&
>> + type == HID_COLLECTION_PHYSICAL)
>> + parser->flags |= HID_FLAG_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_open_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);
>> + }
>> +
>> + /* Reset the local parser environment */
>> + memset(&parser->local, 0, sizeof(parser->local));
>> +
>> + return 0;
>> }
>>
>> /*
>> @@ -690,49 +729,65 @@ 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;
>> + int ret;
>> + 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;
>> + parser = vzalloc(sizeof(struct hid_parser));
>
> Argh, I realize it is inevitable for this patch, but it still makes my
> eyes bleed. The parser takes quite a bit of memory...
Yep, my first attempt was to remove it, then I re-added it with a small
tear...
>
>> + if (!parser)
>> + return -ENOMEM;
>> +
>> + parser->device = hid;
>> +
>> + ret = -EINVAL;
>> 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;
>> +
>> + if (item.format != HID_ITEM_FORMAT_SHORT) {
>> + hid_err(hid, "unexpected long global item\n");
>
> I do not think we should be verbose on errors during scan, for the
> reason stated at the top. Since this goes also for the global parser
> functions, we might have a problem.
yes, I kept it for documenting purposes, but this will double the amount
of logs in the kernel debug output. I'll just convert them into comments
in v2.
>
>> + goto out;
>> + }
>> +
>> + if (dispatch_type[item.type](parser, &item)) {
>> + hid_err(hid, "item %u %u %u %u parsing failed\n",
>> + item.format, (unsigned)item.size,
>> + (unsigned)item.type, (unsigned)item.tag);
>
> Ditto.
Ditto
>
>> + goto out;
>> + }
>> +
>> + if (start == end) {
>> + if (parser->local.delimiter_depth) {
>> + hid_err(hid, "unbalanced delimiter at end of report description\n");
>
> Robustness, see top.
>
>> + goto out;
>> }
>> - } 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;
>
> At the end of the day, It may be best to simply extend this branch as
> the main item type and add whatever you need to detect win8 from
> there.
>
I don't think this would be that simple:
- the usage is given by the HID_ITEM_TYPE_LOCAL branch
- I also need to check the fact that the usage is used as a feature:
this would require setting temporary flags and involve a logic which
would not be very easy to understand.
Furthermore, this makes me think that if a device describes in the
reports a ContactID as a feature, then the current parsing will say that
this is a multitouch device, whereas it should not. (ok, this has no
reasons to appear because it would be dumb, but still...)
>> + ret = 0;
>> + goto out;
>> + }
>> }
>>
>> - return 0;
>> + hid_err(hid, "item fetching failed at offset %d\n", (int)(end - start));
>> +out:
>> + switch (parser->flags) {
>> + case HID_FLAG_MULTITOUCH:
>> + hid->group = HID_GROUP_MULTITOUCH;
>> + break;
>> + case HID_FLAG_SENSOR_HUB:
>> + hid->group = HID_GROUP_SENSOR_HUB;
>> + break;
>> + default:
>> + hid->group = HID_GROUP_GENERIC;
>> + }
>
> Looks odd to switch on flags, but it works pretty well with the rest
> of the patches in the series.
Yep, it's odd. If nobody is against changing the current groups
definitions, we can just keep the group as a bitfield, and it will work
(we just need to sanitize the group at the end).
Cheers,
Benjamin
>
>> +
>> + vfree(parser);
>> + return ret;
>> }
>>
>> /**
>> diff --git a/include/linux/hid.h b/include/linux/hid.h
>> index 5a4e789..7d823db 100644
>> --- a/include/linux/hid.h
>> +++ b/include/linux/hid.h
>> @@ -533,6 +533,9 @@ static inline void hid_set_drvdata(struct hid_device *hdev, void *data)
>> #define HID_GLOBAL_STACK_SIZE 4
>> #define HID_COLLECTION_STACK_SIZE 4
>>
>> +#define HID_FLAG_MULTITOUCH 0x0001
>> +#define HID_FLAG_SENSOR_HUB 0x0002
>> +
>> struct hid_parser {
>> struct hid_global global;
>> struct hid_global global_stack[HID_GLOBAL_STACK_SIZE];
>> @@ -541,6 +544,7 @@ struct hid_parser {
>> unsigned collection_stack[HID_COLLECTION_STACK_SIZE];
>> unsigned collection_stack_ptr;
>> struct hid_device *device;
>> + unsigned flags;
>> };
>>
>> struct hid_class_descriptor {
>> --
>> 1.8.3.1
>>
>
> Thanks,
> Henrik
>
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