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SubjectRe: [PATCH] HID: multitouch: fix calculation of last slot field in multi-touch reports
On Tue, May 29, 2018 at 03:56:55PM -0700, Ben Chan wrote:
> According to [1] and also seemingly agreed by [2], the Scan Time usage
> (0x0D 0x56) is a report level usage, not a contact level usage.
>
> However, the hid-multitouch driver currently includes HID_DG_SCANTIME
> when calculating `td->last_slot_field', which may lead to
> mt_complete_slot() being prematurely called in certain cases (e.g. when
> each touch input report includes more than one contact and the Scan Time
> usage appears before any contact logical collection).
>
> This patch fixes the issue by skipping mt_store_field() on
> HID_DG_SCANTIME, similar to how HID_DG_CONTACTCOUNT and
> HID_DG_CONTACTMAX are handled.
>
> [1] https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-precision-touchpad-required-hid-top-level-collections#windows-precision-touchpad-input-reports
> [2] https://patchwork.kernel.org/patch/1742181/
>
> Fixes: 29cc309d8bf19 ("HID: hid-multitouch: forward MSC_TIMESTAMP")
> Signed-off-by: Ben Chan <benchan@chromium.org>

This looks reasonable to me.

Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

> ---
> drivers/hid/hid-multitouch.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> index dad2fbb0e3f8..161551aab496 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -620,13 +620,16 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
> hid_map_usage(hi, usage, bit, max,
> EV_MSC, MSC_TIMESTAMP);
> input_set_capability(hi->input, EV_MSC, MSC_TIMESTAMP);
> - mt_store_field(usage, td, hi);
> /* Ignore if indexes are out of bounds. */
> if (field->index >= field->report->maxfield ||
> usage->usage_index >= field->report_count)
> return 1;
> td->scantime_index = field->index;
> td->scantime_val_index = usage->usage_index;
> + /*
> + * We don't set td->last_slot_field as scan time is
> + * global to the report.
> + */
> return 1;
> case HID_DG_CONTACTCOUNT:
> /* Ignore if indexes are out of bounds. */
> --
> 2.17.0.921.gf22659ad46-goog
>
> --
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--
Dmitry

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