On 1/23/2023 3:02 PM, Thinh Nguyen wrote:
On Mon, Jan 23, 2023, Elson Serrao wrote:
On 1/23/2023 11:33 AM, Thinh Nguyen wrote:
On Sat, Jan 21, 2023, Thinh Nguyen wrote:
On Fri, Jan 20, 2023, Alan Stern wrote:
On Sat, Jan 21, 2023 at 02:02:36AM +0000, Thinh Nguyen wrote:
On Fri, Jan 20, 2023, Alan Stern wrote:
A UDC design might have multiple versions, some supporting remote wakeup
and others not. But drivers generally use a single static
usb_gadget_ops structure, and they don't modify it at runtime to account
for hardware differences. So if a single driver controls those multiple
versions, you can't rely on the presence of gadget->ops->wakeup to
indicate whether there actually is hardware remote wakeup support.
Ideally, the usb_gadget structure should have a wakeup_capable flag
which the UDC driver would set appropriately (probably during its probe
routine).
I was thinking that it can be handled by the
usb_gadget_enable_remote_wakeup() so we can do away with the
wakeup_capable flag.
usb_gadget_enable_remote_wakeup() gets called when the gadget or
function is suspended, right? But a gadget driver may want to know long
before that whether the UDC supports remote wakeup, in order to set up
its config descriptor correctly.
No, this is to be called during set configuration. If the configuration
doesn't support remote wakeup, the device should not be able to send
remote wakeup.
On second thought, you're right about the descriptor. It's better to
warn and prevent the remote wakeup bit from being set in the descriptor
if the UDC doesn't support remote wakeup. Warning the user at set
configuration is too late.
So, we need both rw_capable flag and usb_gadget_enable_remote_wakeup().
Thanks,
Thinh
Do we need usb_gadget_enable_remote_wakeup() gadget-op ?
As per the discussion, we can have rw_capable flag in usb_gadget struct and
set it during gagdet init/probe if the UDC supports resume signalling OR
wants the remote wakeup feature to be enabled.
This flag now represents UDC capability to initiate resume signalling.
During enumeration phase, when preparing the config descriptor we can use
gadget->rw_capable flag to rightly modify the remote wakeup
bit. Based on this, host will decide whether to arm the device for remote
wakeup or not.
If the configuration doesn't allow remote wakeup, the device should not
be able to send signal to wake up the host regardless whether the host
armed the device for remote wake or not.
The rw_capable flag will inform the composite layer whether the UDC is
capable of remote wakeup. The composite layer needs to tell the UDC
whether the configuration allows for remote wakeup.
Whether it's usb_gadget_enable_remote_wakeup() or the remote wakeup bit
in the bmAttribute, the composite layer needs to communicate that to the
controller driver. But we should not expect the UDC driver to parse for
that bit. The prepared control transfer from the the composite layer
should be abstracted from the UDC driver.
For gadget->ops->wakeup callback support we already have explicit checks
when invoking this gadget op and device wont be able to send remote wakeup
if callback support doesn't exist.
Please let me know if I am missing something.
As mentioned previously, we should also warn the user if the UDC doesn't
support remote wakeup and prevent the remote wakeup bit being set in the
descriptor.
Let me know if it makes sense.
Thanks,
Thinh
Sure. That makes sense.
As discussed I will modify this patch like below
1.)gadget->rw_capable flag to represent the UDC wakeup capability. Used
to configure/modify rw bit in bmAtrributes before sending ConfigDesc.
Also warn the user if rw bit is set but UDC doesnt support it.
2.) usb_gadget_enable_remote_wakeup() gadget op for composite layer to
inform UDC layer. Maintain an internal flag in UDC driver to guard
against invoking wakeup callbacks when user has not configured for
remote wakeup.
Thanks
Elson
