> 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).
