Re: [PATCH 1/1] xhci: add USB2 test mode support

[Alexander Stein <alexander.stein@systec-electronic.com>]

On Wednesday 08 February 2017 13:53:30, Greg Kroah-Hartman wrote:
> On Wed, Feb 08, 2017 at 11:26:35AM +0100, Alexander Stein wrote:
> > This patch adds support for USB2 test mode (Test_J, Test_K,
> > Test_SE0_NAK and Test_Packet) per XHCI spec 4.19.6.
> 
> What does that mean "in English"?  In other words, why do we want this?
> What does it provide for a user?  Why do we care?

USB2 test mode is a required hardware feature for system integrators 
validating their hardware according to USB spec, regarding signal strength and 
stuff. It is purely a hardware test feature.

> > @@ -1134,6 +1137,64 @@ int xhci_hub_control(struct usb_hcd *hcd, u16
> > typeReq, u16 wValue,> 
> >  			temp |= PORT_U2_TIMEOUT(timeout);
> >  			writel(temp, port_array[wIndex] + PORTPMSC);
> >  			break;
> > 
> > +		case USB_PORT_FEAT_TEST:
> > +			/* 4.19.6 Port Test Modes (USB2 Test Mode) */
> > +			if (hcd->speed != HCD_USB2)
> > +				goto error;
> > +
> > +			/* FIXME: Test_Force_Enable case to be implemented */
> > +			if (selector < TEST_J || selector > TEST_PACKET)
> > +				goto error;
> > +
> > +			/* Disable all Device Slots */
> > +			for (i = 0; i < MAX_HC_SLOTS; i++) {
> > +				struct xhci_command *command;
> > +
> > +				if (!xhci->dcbaa->dev_context_ptrs[i])
> > +					continue;
> > +				command = xhci_alloc_command(xhci, false,
> > +						false, GFP_ATOMIC);
> > +				if (!command)
> > +					return -ENOMEM;
> > +				if (xhci_queue_slot_control(xhci, command,
> > +						TRB_DISABLE_SLOT, i)) {
> > +					xhci_err(xhci,
> > +						"Disable slot[%d] fail!\n", i);
> > +						goto error;
> > +					}
> > +				xhci_dbg(xhci, "Disable Slot[%d].\n", i);
> > +			}
> > +
> > +			/* Put all ports to the Disable state by clear PP */
> > +			xhci_dbg(xhci, "Disable all port (PP = 0)\n");
> > +			for (i = 0; i < max_ports; i++) {
> > +				temp = readl(port_array[i]);
> > +				temp &= ~PORT_POWER;
> > +				writel(temp, port_array[i]);
> > +			}
> > +
> > +			/* Stop the controller */
> > +			xhci_dbg(xhci, "Stop controller\n");
> > +			temp = readl(&xhci->op_regs->command);
> > +			temp &= ~CMD_RUN;
> > +			writel(temp, &xhci->op_regs->command);
> > +
> > +			if (xhci_handshake(&xhci->op_regs->status,
> > +				STS_HALT, STS_HALT, XHCI_MAX_HALT_USEC)) {
> > +				xhci_warn(xhci, "Stop controller timeout\n");
> > +				return -ETIMEDOUT;
> > +			}
> > +
> > +			/* Disable runtime PM for test mode */
> > +			pm_runtime_forbid(hcd->self.controller);
> > +
> > +			/* Set PORTPMSC.PTC field for selected test mode */
> > +			xhci_dbg(xhci, "Enter Test Mode: %d\n", selector);
> > +			temp = readl(port_array[wIndex] + PORTPMSC);
> > +			temp |= selector << 28;
> > +			writel(temp, port_array[wIndex] + PORTPMSC);
> > +
> > +			break;
> 
> What does this "test mode" do?  Where does it report the information?
> Who can use it?

Useually you need an oscilloscope and have to enable those test modes on the 
hardware. This will send some specific test patterns on D+/D-. There is no 
report available (in linux itself) as it is purely externaly visible.
Regular USB usage is not possible at that time.
Anyone (well access to e.g. /dev/bus/usb/001/001 provided) can use it by 
sending appropriate USB_PORT_FEAT_TEST requests to the hub.
The same feature for ehci based hosts is already available at 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/host/ehci-hub.c#n1267

Best regards,
Alexander
-- 
Dipl.-Inf. Alexander Stein
SYS TEC electronic GmbH
alexander.stein@systec-electronic.com

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