Re: [PATCH] HID: multitouch: Do not fetch initial feature reports for Win8 devices

[Benjamin Tissoires]

Hi Mika,

On Sep 24 2015 or thereabouts, Mika Westerberg wrote:
> Some newer Intel Skylake based Dell laptops with Win8 precision touchpad
> fail when initial feature reports are fetched from it. Below is an

That is unfortunate.

> example output with some additional debug included:
> 
>  i2c_hid i2c-DLL0704:01: Fetching the HID descriptor
>  i2c_hid i2c-DLL0704:01: __i2c_hid_command: cmd=20 00
>  i2c_hid i2c-DLL0704:01: HID Descriptor: 1e 00 00 01 99 02 21 00 24 ...
>  ...
>  i2c_hid i2c-DLL0704:01: i2c_hid_get_report
>  i2c_hid i2c-DLL0704:01: __i2c_hid_command: cmd=22 00 38 02 23 00
>  i2c_hid i2c-DLL0704:01: report (len=4): 04 00 08 05
>  i2c_hid i2c-DLL0704:01: report id 13
>  i2c_hid i2c-DLL0704:01: i2c_hid_get_report
>  i2c_hid i2c-DLL0704:01: __i2c_hid_command: cmd=22 00 3d 02 23 00
>  i2c_hid i2c-DLL0704:01: failed to retrieve report from device.
>  i2c_hid i2c-DLL0704:01: report id 7
>  i2c_hid i2c-DLL0704:01: i2c_hid_get_report
>  i2c_hid i2c-DLL0704:01: __i2c_hid_command: cmd=22 00 37 02 23 00
>  i2c_hid i2c-DLL0704:01: report (len=259): 03 01 07 fc 28 fe 84 40 ...
>  i2c_hid i2c-DLL0704:01: report id 4
>  i2c_hid i2c-DLL0704:01: i2c_hid_get_report
>  i2c_hid i2c-DLL0704:01: __i2c_hid_command: cmd=22 00 34 02 23 00
> 
> We manage to fetch few reports but then the touchpad dies:
> 
>  i2c_designware i2c_designware.1: i2c_dw_handle_tx_abort: lost arbitration
>  i2c_hid i2c-DLL0704:01: failed to retrieve report from device.
> 
> it eventually pulls the whole I2C bus low:
> 
>  i2c_designware i2c_designware.1: controller timed out
>  i2c_hid i2c-DLL0704:01: failed to set a report to device.
> 
> Fix this by preventing initial feature report fetch for Win8 devices. It
> should not be needed anyway according to [1] because the two "GET"
> feature reports for these devices are about device capabilities and Win8
> certification status which are not related to input events.
> 
> [1] https://msdn.microsoft.com/en-us/library/windows/hardware/dn467314(v=vs.85).aspx
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> ---
>  drivers/hid/hid-multitouch.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> index 426b2f1a3450..1911f7698511 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -1020,14 +1020,16 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
>  	/*
>  	 * Handle special quirks for Windows 8 certified devices.
>  	 */
> -	if (id->group == HID_GROUP_MULTITOUCH_WIN_8)
> +	if (id->group == HID_GROUP_MULTITOUCH_WIN_8) {
>  		/*
>  		 * Some multitouch screens do not like to be polled for input
> -		 * reports. Fortunately, the Win8 spec says that all touches
> -		 * should be sent during each report, making the initialization
> -		 * of input reports unnecessary.
> +		 * and feature reports. Fortunately, the Win8 spec says that all
> +		 * touches should be sent during each report, making the
> +		 * initialization of input reports unnecessary.
>  		 */
>  		hdev->quirks |= HID_QUIRK_NO_INIT_INPUT_REPORTS;
> +		hdev->quirks |= HID_QUIRK_NO_INIT_REPORTS;

Problem is that with this quirk, event the features we are interested in
(and that the device should support or Microsoft would complain) are not
pre-read. I think we should set HID_QUIRK_NO_INIT_REPORTS (and remove
HID_QUIRK_NO_INIT_INPUT_REPORTS BTW), and set up a quirk to actually
retrieve the value of the feature in mt_feature_mapping. This way, we
would be sure to only probe for features that are supported (contact
count is the most important one).

Cheers,
Benjamin

> +	}
>  
>  	td = devm_kzalloc(&hdev->dev, sizeof(struct mt_device), GFP_KERNEL);
>  	if (!td) {
> -- 
> 2.5.1
> 
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