Re: [PATCH] USB: core: Fix oversight in SuperSpeed initialization

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Aug 11, 2023 at 01:38:46PM -0400, Alan Stern wrote:
> Commit 85d07c556216 ("USB: core: Unite old scheme and new scheme
> descriptor reads") altered the way USB devices are enumerated
> following detection, and in the process it messed up the
> initialization of SuperSpeed (or faster) devices:
> 
> [   31.650759] usb 2-1: new SuperSpeed Plus Gen 2x1 USB device number 2 using xhci_hcd
> [   31.663107] usb 2-1: device descriptor read/8, error -71
> [   31.952697] usb 2-1: new SuperSpeed Plus Gen 2x1 USB device number 3 using xhci_hcd
> [   31.965122] usb 2-1: device descriptor read/8, error -71
> [   32.080991] usb usb2-port1: attempt power cycle
> ...
> 
> The problem was caused by the commit forgetting that in SuperSpeed or
> faster devices, the device descriptor uses a logarithmic encoding of
> the bMaxPacketSize0 value.  (For some reason I thought the 255 case in
> the switch statement was meant for these devices, but it isn't -- it
> was meant for Wireless USB and is no longer needed.)
> 
> We can fix the oversight by testing for buf->bMaxPacketSize0 = 9
> (meaning 512, the actual maxpacket size for ep0 on all SuperSpeed
> devices) and straightening out the logic that checks and adjusts our
> initial guesses of the maxpacket value.
> 
> Reported-and-tested-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> Closes: https://lore.kernel.org/linux-usb/20230810002257.nadxmfmrobkaxgnz@synopsys.com/
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> Fixes: 85d07c556216 ("USB: core: Unite old scheme and new scheme descriptor reads")
> 
> ---
> 
>  drivers/usb/core/hub.c |   36 ++++++++++++++++++++++++------------
>  1 file changed, 24 insertions(+), 12 deletions(-)

Process nit, when you add a patch to an existing patch series like this,
when I run `b4` to download and apply the patch, it sucks in the
original patch series, not this add-on patch (which then of course fails
as the original patch series was already applied.)

So, if it's easy enough, can you just send add-on patches for stuff that
has been applied, as a new thread?  That way the tools handle it
automatically and I don't have to hand edit/apply the patch?

thanks,

greg k-h