linux-kernel - [PATCH] usb: ohci: Default to per-port over-current protection

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Date:   Wed,  9 Sep 2020 15:57:34 +1200
From:   Hamish Martin <hamish.martin@...iedtelesis.co.nz>
To:     stern@...land.harvard.edu, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hamish Martin <hamish.martin@...iedtelesis.co.nz>
Subject: [PATCH] usb: ohci: Default to per-port over-current protection

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 patch results in the following configuration changes depending
on quirks:
- For quirk OHCI_QUIRK_SUPERIO no changes. These systems remain set up
  for ganged power switching and no over-current protection.
- For quirk OHCI_QUIRK_AMD756 or OHCI_QUIRK_HUB_POWER power switching
  remains at none, while over-current protection is now guaranteed to be
  set to per-port rather than the previous behaviour where it was either
  none or global over-current protection depending on the value at
  function entry.

Suggested-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Hamish Martin <hamish.martin@...iedtelesis.co.nz>
---
 drivers/usb/host/ohci-hcd.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
index dd37e77dae00..8ab81f6ab150 100644
--- a/drivers/usb/host/ohci-hcd.c
+++ b/drivers/usb/host/ohci-hcd.c
@@ -673,20 +673,25 @@ static int ohci_run (struct ohci_hcd *ohci)
 
 	/* handle root hub init quirks ... */
 	val = roothub_a (ohci);
-	val &= ~(RH_A_PSM | RH_A_OCPM);
+	/* Configure for per-port over-current protection by default */
+	val &= ~RH_A_NOCP;
+	val |= RH_A_OCPM;
 	if (ohci->flags & OHCI_QUIRK_SUPERIO) {
-		/* NSC 87560 and maybe others */
+		/* NSC 87560 and maybe others.
+		 * Ganged power switching, no over-current protection.
+		 */
 		val |= RH_A_NOCP;
-		val &= ~(RH_A_POTPGT | RH_A_NPS);
-		ohci_writel (ohci, val, &ohci->regs->roothub.a);
+		val &= ~(RH_A_POTPGT | RH_A_NPS | RH_A_PSM | RH_A_OCPM);
 	} else if ((ohci->flags & OHCI_QUIRK_AMD756) ||
 			(ohci->flags & OHCI_QUIRK_HUB_POWER)) {
 		/* hub power always on; required for AMD-756 and some
-		 * Mac platforms.  ganged overcurrent reporting, if any.
+		 * Mac platforms.
 		 */
+		val &= ~RH_A_PSM;
 		val |= RH_A_NPS;
-		ohci_writel (ohci, val, &ohci->regs->roothub.a);
 	}
+	ohci_writel(ohci, val, &ohci->regs->roothub.a);
+
 	ohci_writel (ohci, RH_HS_LPSC, &ohci->regs->roothub.status);
 	ohci_writel (ohci, (val & RH_A_NPS) ? 0 : RH_B_PPCM,
 						&ohci->regs->roothub.b);
-- 
2.28.0