Re: [PATCH] usb/host/pci-quirks: Only reset USB bus on NVIDIA devices

[Paul Menzel]

[Taking stable@ out of CC. I just started to use `git send-email`.]


Dear Alan,


Am 02.07.2018 um 17:45 schrieb Alan Stern:
> On Sun, 1 Jul 2018, Paul Menzel wrote:
>
> > Currently, on the AMD board Asus F2A85-M Pro there is a 100 ms delay as
> > the USB bus of each of the two OHCI PCI devices is reset. As a 50 ms
> > delay is done per the USB specification.
> >
> > Commit c6187597 (OHCI: final fix for NVIDIA problems (I hope))
> > unconditionally does the bus reset for
> >   all chipsets, while it was only doen for NVIDIA chipsets before.
>
> I don't follow this at all.  Prior to that commit, the bus reset (i.e.,
>
> 	writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL);
>
> ) was performed unconditionally for _all_ controllers.  (However, the
> 50-ms delay was used only for NVIDIA hardware.)  Following that commit,
> the reset is performed for all controllers, but only if the HCFS
> bitfield is nonzero.
>
> > As it should not be needed for non-NVIDIA chipsets, only do the reset
> > for Nvidia devices.
>
> Therefore this reasoning is wrong.

True. Thank you for checking that.

> > Tested on Asus F2A85-M PRO and ASRock E350M1. The USB keyboard works and
> > the LUKS passphrase can be entered.
>
> Unfortunately, there is a wide variety of OHCI controller hardware
> available.  Something that works on one or two controllers might not
> work on another.

The problem is, that currently 100 ms sleep is over 10 % of the overall
execution time of the Linux kernel here. So I really like to not sleep 
if itâs not needed.

> Besides, doesn't it seem like a bad idea to reset the controller while
> leaving devices on the USB bus in whatever state they happened to be?

Yes, itâs probably not optimal.

I wonder if the reset is needed, if the firmware has already initialized
the device.


Kind regards,

Paul