On 9/30/22 23:58, Christian Kohlschütter wrote:
On 30. Sep 2022, at 04:42, Marek Vasut <ma...@denx.de> wrote:
On 9/26/22 23:55, Christian Kohlschütter wrote:
On 26. Sep 2022, at 01:45, Marek Vasut <ma...@denx.de> wrote:
On 9/25/22 16:46, Christian Kohlschütter wrote:
When detecting USB storage devices, we currently skip everything that is
not marked as "undefined device class".
Composite devices such as tinyusb's CDC+MSC identify as "miscellaneous"
(class 0xEF).
Introduce a new constant, USB_CLASS_MISC (0xEF), and allow the detection
process to proceed for USB devices with this device class.
What does Linux do with such a device , is there a specific quirk or does it
simply not check the bDeviceClass at all ?
I didn't see any relevant checks in drivers/usb/storage, however changing the bDeviceClass from
"MISC" (0xEF) to "UNSPECIFIED"/"PER_INTERFACE" (0x00) causes the device to be
no longer detected by either Linux or macOS, but it would work with U-Boot (i.e., without the change).
macOS' USB prober would report the USB device as "unconfigured". On Linux,
using usbutils but not busybox, lsusb would actually hang.
I think it's a good idea to keep the set of permitted device classes to a
minimum (0x00 / 0xEF) and abort early in all other cases. This way, we can skip
the more elaborate checks in usb_storage_probe for devices that are definitely
not supported.
I think the check in the usb_storage.c is actually correct as-is and the device
you have might be odd.
https://www.usb.org/sites/default/files/usbmassbulk_10.pdf
"
4.1 Device Descriptor
Each USB device has one device descriptor (per USB Specification). The device
shall specify the device class and subclass codes in the interface descriptor,
and not in the device descriptor.
...
4 | bDeviceClass | Byte | 00h | Class is specified in the interface descriptor.
...
NOTE: Information in this table is from the USB Specification version 1.1 table
9-7. Bold text has been added for clarifications when using these descriptors
with this specification.
"
And then
"
4.3 Interface Descriptors
The device shall support at least one interface, known herein as the Bulk-Only
Data Interface. The Bulk-Only Data Interface uses three endpoints.
Composite mass storage devices may support additional interfaces, to provide
other features such as audio or video capabilities. This specification does not
define such interfaces.
The interface may have multiple alternate settings. The host shall examine each
of the alternate settings to look for the bInterfaceProtocol and
bInterfaceSubClass it supports optimally.
"
If I read this right, then such a composite device like you have should have
bDeviceClass=0x00 and two Interface descriptors, one for the mass storage
device and one for CDC ?
See
https://github.com/hathach/tinyusb/blob/master/examples/device/cdc_msc/src/usb_descriptors.c
for an example of such a device. It has one mass storage device and one CDC.
Changing the device class to 0x00 breaks support on Linux and macOS (I didn't
try Windows).
The question is -- does the aforementioned device conform to the USB-IF
specification ? I think it does not, but luckily it could be fixed in
software on the tinyusb side.
