RE: [PATCH v2 2/3] usb: gadget: composite: Support eUSB2v2 bulk MPS update request

[Pawel Laszczak]

>
>On 8/26/2026 4:54 PM, Pawel Laszczak via B4 Relay wrote:
>> From: Pawel Laszczak <pawell@xxxxxxxxxxx>
>>
>> Add support for eUSB2v2 1024-byte Bulk MPS negotiation to the Gadget
>> Composite framework.
>>
>> If 'gadget->is_eusb2v2' is set, force bcdUSB to 0x0230 and bMaxPacketSize0
>> to 64 bytes. Handle the USB_DEVICE_BULK_MAX_PACKET_UPDATE feature
>request
>> by introducing eusb2_update_mps_bulk(), which dynamically updates the
>> wMaxPacketSize of all HS Bulk endpoint descriptors to 1024 bytes before
>> the device is configured.
>>
>> Signed-off-by: Pawel Laszczak <pawell@xxxxxxxxxxx>
>> ---
>> Changes in v2:
>> - composite.c: CLEAR_FEATURE(BULK_MAX_PACKET_UPDATE) is not defined in
>the
>>    eUSB2v2 spec; stall it instead of incorrectly setting 1024-byte mode.
>> - restore MPS in __composite_disconnect
>> ---
>>   drivers/usb/gadget/composite.c | 68
>++++++++++++++++++++++++++++++++++++++----
>>   include/linux/usb/gadget.h     |  2 ++
>>   2 files changed, 64 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
>> index dc3664374596..f0246e25f2b5 100644
>> --- a/drivers/usb/gadget/composite.c
>> +++ b/drivers/usb/gadget/composite.c
>> @@ -924,6 +924,48 @@ static void device_qual(struct usb_composite_dev
>*cdev)
>>   }
>>
>>   /*-------------------------------------------------------------------------*/
>> +static void eusb2_update_ep_mps(struct usb_descriptor_header *header,
>__le16 mps)
>> +{
>> +	struct usb_endpoint_descriptor *epd;
>> +
>> +	if (header->bDescriptorType != USB_DT_ENDPOINT)
>> +		return;
>> +
>> +	epd = (void *)header;
>> +	if (usb_endpoint_xfer_bulk(epd))
>> +		epd->wMaxPacketSize = mps;
>> +}
>> +
>> +static int eusb2_update_mps_bulk(struct usb_composite_dev *cdev, bool
>set)
>> +{
>> +	__le16 mps = cpu_to_le16(set ? 1024 : 512);
>> +	struct usb_gadget *gadget = cdev->gadget;
>> +	struct usb_configuration *config;
>> +	struct usb_function *f;
>> +
>> +	if (!gadget->is_eusb2v2)
>> +		return -EINVAL;
>> +
>> +	if (set && gadget->state >= USB_STATE_CONFIGURED)
>> +		return -EINVAL;
>> +
>> +	list_for_each_entry(config, &cdev->configs, list) {
>> +		if (!config->highspeed)
>> +			continue;
>> +
>> +		list_for_each_entry(f, &config->functions, list) {
>> +			struct usb_descriptor_header **desc = f-
>>hs_descriptors;
>> +
>> +			if (!desc)
>> +				continue;
>> +
>> +			for (; *desc; desc++)
>> +				eusb2_update_ep_mps(*desc, mps);
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>>
>>   static void reset_config(struct usb_composite_dev *cdev)
>>   {
>> @@ -971,8 +1013,10 @@ static int set_config(struct usb_composite_dev
>*cdev,
>>   		if (result < 0)
>>   			goto done;
>>   	} else { /* Zero configuration value - need to reset the config */
>> -		if (cdev->config)
>> +		if (cdev->config) {
>>   			reset_config(cdev);
>> +			eusb2_update_mps_bulk(cdev, false);
>> +		}
>>   		result = 0;
>>   	}
>>
>> @@ -1807,7 +1851,11 @@ composite_setup(struct usb_gadget *gadget,
>const struct usb_ctrlrequest *ctrl)
>>   				count_configs(cdev, USB_DT_DEVICE);
>>   			cdev->desc.bMaxPacketSize0 =
>>   				cdev->gadget->ep0->maxpacket;
>> -			if (gadget_is_superspeed(gadget)) {
>> +
>> +			if (gadget->is_eusb2v2) {
>> +				cdev->desc.bcdUSB = cpu_to_le16(0x0230);
>> +				cdev->desc.bMaxPacketSize0 = 64;
>> +			} else if (gadget_is_superspeed(gadget)) {
>>   				if (gadget->speed >= USB_SPEED_SUPER) {
>>   					cdev->desc.bcdUSB =
>cpu_to_le16(0x0320);
>>   					cdev->desc.bMaxPacketSize0 = 9;
>> @@ -2005,12 +2053,19 @@ composite_setup(struct usb_gadget *gadget,
>const struct usb_ctrlrequest *ctrl)
>>   	 */
>>   	case USB_REQ_CLEAR_FEATURE:
>>   	case USB_REQ_SET_FEATURE:
>> -		if (!gadget_is_superspeed(gadget))
>> -			goto unknown;
>> -		if (ctrl->bRequestType != (USB_DIR_OUT |
>USB_RECIP_INTERFACE))
>> -			goto unknown;
>>   		switch (w_value) {
>> +		case USB_DEVICE_BULK_MAX_PACKET_UPDATE:
>> +			if (ctrl->bRequestType != (USB_DIR_OUT |
>USB_RECIP_DEVICE))
>> +				goto unknown;
>> +			if (ctrl->bRequest != USB_REQ_SET_FEATURE)
>> +				goto unknown;
>> +			value = eusb2_update_mps_bulk(cdev, true);
>Here both USB_REQ_CLEAR_FEATURE and USB_REQ_SET_FEATURE fall through
>to
>the same switch, and USB_DEVICE_BULK_MAX_PACKET_UPDATE unconditionally
>calls eusb2_update_mps_bulk(cdev, true) regardless of which request type
>was received.
>
>The CLEAR_FEATURE may request should revert the MPS back to the default
>by calling eusb2_update_mps_bulk(cdev, false), but instead it performs
>the same action as SET_FEATURE.
>
>Is this required distinguished using ctrl->bRequest to check whether
>this is a SET or CLEAR operation?

Hi Selva,

Thank you for the review.

The eUSB2v2 specification does not define CLEAR_FEATURE for the
BULK_MAX_PACKET_UPDATE feature selector, so the device is expected to
respond with a STALL in that case.

The check on line:

if (ctrl->bRequest != USB_REQ_SET_FEATURE)
        goto unknown;

already handles this: when CLEAR_FEATURE falls through to the
USB_DEVICE_BULK_MAX_PACKET_UPDATE case, it hits this condition and
jumps to 'unknown', which results in a STALL being returned to the
host. So eusb2_update_mps_bulk(cdev, true) is never called for
CLEAR_FEATURE.

MPS restoration to 512 bytes is handled separately on disconnect and
deconfiguration events (__composite_disconnect and set_config).

Thanks,
Pawel
>
>
>Thanks,
>Selva
>> +			break;
>>   		case USB_INTRF_FUNC_SUSPEND:
>> +			if (!gadget_is_superspeed(gadget))
>> +				goto unknown;
>> +			if (ctrl->bRequestType != (USB_DIR_OUT |
>USB_RECIP_INTERFACE))
>> +				goto unknown;
>>   			if (!cdev->config || intf >= MAX_CONFIG_INTERFACES)
>>   				break;
>>   			f = cdev->config->interface[intf];
>> @@ -2293,6 +2348,7 @@ static void __composite_disconnect(struct
>usb_gadget *gadget)
>>   	 * disconnect callbacks?
>>   	 */
>>   	spin_lock_irqsave(&cdev->lock, flags);
>> +	eusb2_update_mps_bulk(cdev, false);
>>   	cdev->suspended = 0;
>>   	if (cdev->config)
>>   		reset_config(cdev);
>> diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
>> index 8285b19a25e0..3c554fe95f87 100644
>> --- a/include/linux/usb/gadget.h
>> +++ b/include/linux/usb/gadget.h
>> @@ -420,6 +420,7 @@ struct usb_gadget_ops {
>>    * @wakeup_armed: True if gadget is armed by the host for remote wakeup.
>>    * @irq: the interrupt number for device controller.
>>    * @id_number: a unique ID number for ensuring that gadget names are
>distinct
>> + * @is_eusb2v2: True if controller is Embedded usb2.
>>    *
>>    * Gadgets have a mostly-portable "gadget driver" implementing device
>>    * functions, handling all usb configurations and interfaces.  Gadget
>> @@ -483,6 +484,7 @@ struct usb_gadget {
>>   	unsigned			lpm_capable:1;
>>   	unsigned			wakeup_capable:1;
>>   	unsigned			wakeup_armed:1;
>> +	unsigned			is_eusb2v2:1;
>>   	int				irq;
>>   	int				id_number;
>>   };
>>