On Sun, Dec 27, 2020 at 12:22:34PM +0100, Paul Kocialkowski wrote:

Hi,

Sorry it has taken so long to respond to this.  The holidays intervened, 
but that's no excuse.

On Fri 11 Sep 20, 09:25, Hamish Martin wrote:

quoted

Some integrated OHCI controller hubs do not expose all ports of the hub
to pins on the SoC. In some cases the unconnected ports generate
spurious over-current events. For example the Broadcom 56060/Ranger 2 SoC
contains a nominally 3 port hub but only the first port is wired.

Default behaviour for ohci-platform driver is to use global over-current
protection mode (AKA "ganged"). This leads to the spurious over-current
events affecting all ports in the hub.

We now alter the default to use per-port over-current protection.

This specific patch lead to breaking OHCI on my mom's laptop (whom was about
to buy a new one thinking the hardware had failed). I get no OHCI interrupt at
all and no USB 1 device is ever detected.

I haven't really found a reasonable explanation about why that is, but here
are some notes I was able to collect:
- The issue showed up on 5.8,18 and 5.9.15, which don't include the patch
  from this series that sets distrust_firmware = false; This results in the NPS
  bit being set via OHCI_QUIRK_HUB_POWER.
- Adding val &= ~RH_A_PSM; (as was done before this change) solves the issue
  which is weird because the bit is supposed to be inactive when NPS is set;
- Setting ohci_hcd.distrust_firmware=0 in the cmdline results in not setting
  the NPS bit and also solves the issue;
- The initial value of the register at function entry is 0x1001104 (PSM bit
  is set, NPS is unset);
- The OHCI controller is the following:
00:03.0 USB controller: Silicon Integrated Systems [SiS] USB 1.1 Controller (rev 0f) (prog-if 10 [OHCI])
	Subsystem: ASUSTeK Computer Inc. Device 1aa7

Great reporting -- thanks.

Does that make any sense to you?

I really wonder what a proper fix could be and here are some suggestions:
- Adding a specific quirk to clear the PSM bit for this hardware which seems to
  consider the bit regardless of NPS;

We don't need a quirk for this.  There shouldn't be anything wrong with 
_always_ clearing PSM whenever NPS is set, since the controller is 
supposed to ignore PSM under that condition.

Would you like to submit a patch for this?

- Adding the patch that sets distrust_firmware = false to stable branches;

That's certainly reasonable.  Nobody has reported any problems caused by 
that patch, so adding it to the stable branches should be safe enough.

What do you think?

We could even do both.  That would help if, for example, somebody 
decided to set ohci_hcd.distrust_firmware=true explicitly.

Greg, in the meantime can we have commit c4005a8f65ed ("usb: ohci: Make 
distrust_firmware param default to false") added to all the stable 
kernels which have back-ported versions of commit b77d2a0a223b?

Alan Stern