[U-Boot] [PATCH] usb: kbd: don't use int xfers when polling via ctrl xfers

[Stephen Warren]

On 11/15/2015 12:40 PM, Hans de Goede wrote:
> Hi,
>
> On 11/13/2015 09:34 PM, Stephen Warren wrote:
>> From: Stephen Warren <swarren at nvidia.com>
>>
>> When CONFIG_SYS_USB_EVENT_POLL_VIA_CONTROL_EP is enabled, use a
>> GET_REPORT control transfer to retrieve the initial state of the
>> keyboard. This matches the technique used to poll the keyboard state.
>> This is useful since it eliminates the remaining use of interrupt
>> transfers from the USB keyboard driver, which allows it to work with
>> USB HCD that don't support interrupt transfers.
>>
>> Cc: Hans de Goede <hdegoede at redhat.com>
>> Signed-off-by: Stephen Warren <swarren at nvidia.com>
>> ---
>> Are there any disadvantages to using control transfers over interrupt
>> transfers? I'm not aware of any, but I assume there must be a reason
>> that U-Boot typically uses interrupt transfers.
>
> I know of at least 2 issues with using control transfers, and IMHO we
> should try to just remove support for control transfers from the usb
> kbd drivers.
>
> The 2 known issues are:
>
> 1) I've some cheap wireless keyboards where the usb-dongle does not
> support the ctrl method of polling and things simply do not work
> when using it.
>
> 2) My USB+DVI kvm switch will report keys as pressed to all connected
> machines, even those without focus when using the ctrl method (this makes
> sense since other control methods must work without focus to keep the
> os on the machine happy).

Interesting; Marek observed the opposite i.e. some keyboards that only 
worked with control transfers.

However, I think that fixing the existing "use control transfers" 
support so that it exclusively uses control transfers is still 
reasonable? Perhaps the issues with control transfers affect my decision 
not to implement interrupt transfers at all in my USB driver, but 
probably not this patch.

Perhaps a useful future extension would be to register two keyboard 
drivers; one explicitly using interrupt transfers and one using control 
transfers, so that the user can set stdin depending on which mode of 
operation they want.