[PATCH AUTOSEL 5.4 020/109] usb: gadget: composite: Allow bMaxPower=0 if self-powered

From: Sasha Levin
Date: Thu Sep 09 2021 - 08:55:15 EST

From: Jack Pham <jackp@xxxxxxxxxxxxxx>

[ Upstream commit bcacbf06c891374e7fdd7b72d11cda03b0269b43 ]

Currently the composite driver encodes the MaxPower field of
the configuration descriptor by reading the c->MaxPower of the
usb_configuration only if it is non-zero, otherwise it falls back
to using the value hard-coded in CONFIG_USB_GADGET_VBUS_DRAW.
However, there are cases when a configuration must explicitly set
bMaxPower to 0, particularly if its bmAttributes also has the
Self-Powered bit set, which is a valid combination.

This is specifically called out in the USB PD specification section
9.1, in which a PDUSB device "shall report zero in the bMaxPower
field after negotiating a mutually agreeable Contract", and also
verified by the USB Type-C Functional Test TD.4.10.2 Sink Power
Precedence Test.

The fix allows the c->MaxPower to be used for encoding the bMaxPower
even if it is 0, if the self-powered bit is also set. An example
usage of this would be for a ConfigFS gadget to be dynamically
updated by userspace when the Type-C connection is determined to be
operating in Power Delivery mode.

Co-developed-by: Ronak Vijay Raheja <rraheja@xxxxxxxxxxxxxx>
Acked-by: Felipe Balbi <balbi@xxxxxxxxxx>
Signed-off-by: Ronak Vijay Raheja <rraheja@xxxxxxxxxxxxxx>
Signed-off-by: Jack Pham <jackp@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210720080907.30292-1-jackp@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/usb/gadget/composite.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 24dad1d78d1e..6bd3fdb925cd 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -481,7 +481,7 @@ static u8 encode_bMaxPower(enum usb_device_speed speed,
unsigned val;

- if (c->MaxPower)
+ if (c->MaxPower || (c->bmAttributes & USB_CONFIG_ATT_SELFPOWER))
val = c->MaxPower;
@@ -905,7 +905,11 @@ static int set_config(struct usb_composite_dev *cdev,

/* when we return, be sure our power usage is valid */
- power = c->MaxPower ? c->MaxPower : CONFIG_USB_GADGET_VBUS_DRAW;
+ if (c->MaxPower || (c->bmAttributes & USB_CONFIG_ATT_SELFPOWER))
+ power = c->MaxPower;
+ else
if (gadget->speed < USB_SPEED_SUPER)
power = min(power, 500U);