[PATCH v2] common: usb-hub: Reset USB 3.0 hubs only

[Marek Vasut]

On 2/19/24 10:49, Shantur Rathore wrote:
> Hi Marek,
> 
> On Wed, Feb 14, 2024 at 9:55 AM Shantur Rathore <i at shantur.com> wrote:
>>
>> Additional testing of the changes introduced in commit 33e06dcbe57a "common:
>> usb-hub: Reset hub port before scanning") revealed that some USB 2.0 and 3.0
>> flash drives didn't work in U-Boot on some Allwinner SoCs that support USB
>> 2.0 interfaces only.  More precisely, some of the tested USB 2.0 and 3.0
>> flash drives failed to be detected and work on an OrangePi Zero 3, based on
>> the Allwinner H616 SoC that supports USB 2.0 only, while the same USB flash
>> drives worked just fine on a Pine64 H64, based on the Allwinner H6 SoC that
>> supports both USB 2.0 and USB 3.0 interfaces.
>>
>> The USB ID of the above-mentioned USB 3.0 flash drive that failed to work is
>> 1f75:0917 (Innostor Technology Corporation IS917 Mass storage), it is 32 GB
>> in size and sold under the PNY brand.  The mentioned USB 2.0 drive is some
>> inexpensive no-name drive with an invalid USB ID.
>>
>> Resetting USB 3.0 hubs only, which this patch introduces to the USB hub
>> resets, has been tested to work as expected, resolving the identified issues
>> on the Allwinner H616, while not introducing any new issues on other tested
>> Allwinner SoCs.  Thus, let's fix it that way.
>>
>> According to the USB 3.0 specification, resetting a USB 3.0 port is required
>> when an attached USB device transitions between different states, such as
>> when it resumes from suspend.  Though, the Linux kernel performs additional
>> USB 3.0 port resets upon initial USB device attachment, as visible in commit
>> 07194ab7be63 ("USB: Reset USB 3.0 devices on (re)discovery") in the kernel
>> source, to ensure proper state of the USB 3.0 hub port and proper USB mode
>> negotiation during the initial USB device attachment and enumeration.
>>
>> These additional types of USB port resets don't exist for USB 2.0 hubs,
>> according the USB 2.0 specification.  The resets seem to be added to the USB
>> 3.0 specification as part of the port and device mode negotiation.
>>
>> The Linux kernel resets USB 3.0 (i.e. SuperSpeed) hubs only, as visible in
>> commit 10d674a82e55 ("USB: When hot reset for USB3 fails, try warm reset.")
>> in the kernel source.  The check for SuperSpeed hubs is performed in a way
>> that also applies to newer SuperSpeed Plus (USB 3.1 or 3.2) hubs as well,
>> which hopefully makes it future proof.

Applied, thanks