usb: raw-gadget: update documentation

A recent patch added reporting of more event types to Raw Gadget.

Update the documentation to reflect that this feature has been
implemented.

Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20231030223158.36636-1-andrey.konovalov@linux.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: raw-gadget: update documentation and Kconfig

Update Raw Gadget documentation and Kconfig. Make the description more
precise and clear, fix typos and grammar mistakes, and do other cleanups.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://lore.kernel.org/r/f4c650c94ae2b910e38819d51109cd5f0b251a2a.1611429174.git.andreyknvl@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: raw-gadget: documentation updates

Mention the issue with fixed UDC addresses.

Links external examples and test suite.

Add more implmenetation details and potential improvements.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

usb: raw-gadget: support stalling/halting/wedging endpoints

Raw Gadget is currently unable to stall/halt/wedge gadget endpoints,
which is required for proper emulation of certain USB classes.

This patch adds a few more ioctls:

- USB_RAW_IOCTL_EP0_STALL allows to stall control endpoint #0 when
there's a pending setup request for it.
- USB_RAW_IOCTL_SET/CLEAR_HALT/WEDGE allow to set/clear halt/wedge status
on non-control non-isochronous endpoints.

Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

usb: raw-gadget: fix gadget endpoint selection

Currently automatic gadget endpoint selection based on required features
doesn't work. Raw Gadget tries iterating over the list of available
endpoints and finding one that has the right direction and transfer type.
Unfortunately selecting arbitrary gadget endpoints (even if they satisfy
feature requirements) doesn't work, as (depending on the UDC driver) they
might have fixed addresses, and one also needs to provide matching
endpoint addresses in the descriptors sent to the host.

The composite framework deals with this by assigning endpoint addresses
in usb_ep_autoconfig() before enumeration starts. This approach won't work
with Raw Gadget as the endpoints are supposed to be enabled after a
set_configuration/set_interface request from the host, so it's too late to
patch the endpoint descriptors that had already been sent to the host.

For Raw Gadget we take another approach. Similarly to GadgetFS, we allow
the user to make the decision as to which gadget endpoints to use.

This patch adds another Raw Gadget ioctl USB_RAW_IOCTL_EPS_INFO that
exposes information about all non-control endpoints that a currently
connected UDC has. This information includes endpoints addresses, as well
as their capabilities and limits to allow the user to choose the most
fitting gadget endpoint.

The USB_RAW_IOCTL_EP_ENABLE ioctl is updated to use the proper endpoint
validation routine usb_gadget_ep_match_desc().

These changes affect the portability of the gadgets that use Raw Gadget
when running on different UDCs. Nevertheless, as long as the user relies
on the information provided by USB_RAW_IOCTL_EPS_INFO to dynamically
choose endpoint addresses, UDC-agnostic gadgets can still be written with
Raw Gadget.

Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

usb: gadget: add raw-gadget interface

USB Raw Gadget is a kernel module that provides a userspace interface for
the USB Gadget subsystem. Essentially it allows to emulate USB devices
from userspace. Enabled with CONFIG_USB_RAW_GADGET. Raw Gadget is
currently a strictly debugging feature and shouldn't be used in
production.

Raw Gadget is similar to GadgetFS, but provides a more low-level and
direct access to the USB Gadget layer for the userspace. The key
differences are:

1. Every USB request is passed to the userspace to get a response, while
GadgetFS responds to some USB requests internally based on the provided
descriptors. However note, that the UDC driver might respond to some
requests on its own and never forward them to the Gadget layer.

2. GadgetFS performs some sanity checks on the provided USB descriptors,
while Raw Gadget allows you to provide arbitrary data as responses to
USB requests.

3. Raw Gadget provides a way to select a UDC device/driver to bind to,
while GadgetFS currently binds to the first available UDC.

4. Raw Gadget uses predictable endpoint names (handles) across different
UDCs (as long as UDCs have enough endpoints of each required transfer
type).

5. Raw Gadget has ioctl-based interface instead of a filesystem-based one.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>