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[PATCH 4.6 056/100] USB: leave LPM alone if possible when binding/unbinding interface drivers

From Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups linux.kernel
Subject [PATCH 4.6 056/100] USB: leave LPM alone if possible when binding/unbinding interface drivers
Date 2016-05-30 23:30 +0200
Message-ID <rECV5-1mL-59@gated-at.bofh.it> (permalink)
References <rECBH-1eG-9@gated-at.bofh.it>
Organization linux.* mail to news gateway

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4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@rowland.harvard.edu>

commit 6fb650d43da3e7054984dc548eaa88765a94d49f upstream.

When a USB driver is bound to an interface (either through probing or
by claiming it) or is unbound from an interface, the USB core always
disables Link Power Management during the transition and then
re-enables it afterward.  The reason is because the driver might want
to prevent hub-initiated link power transitions, in which case the HCD
would have to recalculate the various LPM parameters.  This
recalculation takes place when LPM is re-enabled and the new
parameters are sent to the device and its parent hub.

However, if the driver does not want to prevent hub-initiated link
power transitions then none of this work is necessary.  The parameters
don't need to be recalculated, and LPM doesn't need to be disabled and
re-enabled.

It turns out that disabling and enabling LPM can be time-consuming,
enough so that it interferes with user programs that want to claim and
release interfaces rapidly via usbfs.  Since the usbfs kernel driver
doesn't set the disable_hub_initiated_lpm flag, we can speed things up
and get the user programs to work by leaving LPM alone whenever the
flag isn't set.

And while we're improving the way disable_hub_initiated_lpm gets used,
let's also fix its kerneldoc.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Matthew Giassa <matthew@giassa.net>
CC: Mathias Nyman <mathias.nyman@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/core/driver.c |   40 +++++++++++++++++++++++-----------------
 include/linux/usb.h       |    2 +-
 2 files changed, 24 insertions(+), 18 deletions(-)

--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -284,7 +284,7 @@ static int usb_probe_interface(struct de
 	struct usb_device *udev = interface_to_usbdev(intf);
 	const struct usb_device_id *id;
 	int error = -ENODEV;
-	int lpm_disable_error;
+	int lpm_disable_error = -ENODEV;
 
 	dev_dbg(dev, "%s\n", __func__);
 
@@ -336,12 +336,14 @@ static int usb_probe_interface(struct de
 	 * setting during probe, that should also be fine.  usb_set_interface()
 	 * will attempt to disable LPM, and fail if it can't disable it.
 	 */
-	lpm_disable_error = usb_unlocked_disable_lpm(udev);
-	if (lpm_disable_error && driver->disable_hub_initiated_lpm) {
-		dev_err(&intf->dev, "%s Failed to disable LPM for driver %s\n.",
-				__func__, driver->name);
-		error = lpm_disable_error;
-		goto err;
+	if (driver->disable_hub_initiated_lpm) {
+		lpm_disable_error = usb_unlocked_disable_lpm(udev);
+		if (lpm_disable_error) {
+			dev_err(&intf->dev, "%s Failed to disable LPM for driver %s\n.",
+					__func__, driver->name);
+			error = lpm_disable_error;
+			goto err;
+		}
 	}
 
 	/* Carry out a deferred switch to altsetting 0 */
@@ -391,7 +393,8 @@ static int usb_unbind_interface(struct d
 	struct usb_interface *intf = to_usb_interface(dev);
 	struct usb_host_endpoint *ep, **eps = NULL;
 	struct usb_device *udev;
-	int i, j, error, r, lpm_disable_error;
+	int i, j, error, r;
+	int lpm_disable_error = -ENODEV;
 
 	intf->condition = USB_INTERFACE_UNBINDING;
 
@@ -399,12 +402,13 @@ static int usb_unbind_interface(struct d
 	udev = interface_to_usbdev(intf);
 	error = usb_autoresume_device(udev);
 
-	/* Hub-initiated LPM policy may change, so attempt to disable LPM until
+	/* If hub-initiated LPM policy may change, attempt to disable LPM until
 	 * the driver is unbound.  If LPM isn't disabled, that's fine because it
 	 * wouldn't be enabled unless all the bound interfaces supported
 	 * hub-initiated LPM.
 	 */
-	lpm_disable_error = usb_unlocked_disable_lpm(udev);
+	if (driver->disable_hub_initiated_lpm)
+		lpm_disable_error = usb_unlocked_disable_lpm(udev);
 
 	/*
 	 * Terminate all URBs for this interface unless the driver
@@ -505,7 +509,7 @@ int usb_driver_claim_interface(struct us
 	struct device *dev;
 	struct usb_device *udev;
 	int retval = 0;
-	int lpm_disable_error;
+	int lpm_disable_error = -ENODEV;
 
 	if (!iface)
 		return -ENODEV;
@@ -526,12 +530,14 @@ int usb_driver_claim_interface(struct us
 
 	iface->condition = USB_INTERFACE_BOUND;
 
-	/* Disable LPM until this driver is bound. */
-	lpm_disable_error = usb_unlocked_disable_lpm(udev);
-	if (lpm_disable_error && driver->disable_hub_initiated_lpm) {
-		dev_err(&iface->dev, "%s Failed to disable LPM for driver %s\n.",
-				__func__, driver->name);
-		return -ENOMEM;
+	/* See the comment about disabling LPM in usb_probe_interface(). */
+	if (driver->disable_hub_initiated_lpm) {
+		lpm_disable_error = usb_unlocked_disable_lpm(udev);
+		if (lpm_disable_error) {
+			dev_err(&iface->dev, "%s Failed to disable LPM for driver %s\n.",
+					__func__, driver->name);
+			return -ENOMEM;
+		}
 	}
 
 	/* Claimed interfaces are initially inactive (suspended) and
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1069,7 +1069,7 @@ struct usbdrv_wrap {
  *	for interfaces bound to this driver.
  * @soft_unbind: if set to 1, the USB core will not kill URBs and disable
  *	endpoints before calling the driver's disconnect method.
- * @disable_hub_initiated_lpm: if set to 0, the USB core will not allow hubs
+ * @disable_hub_initiated_lpm: if set to 1, the USB core will not allow hubs
  *	to initiate lower power link state transitions when an idle timeout
  *	occurs.  Device-initiated USB 3.0 link PM will still be allowed.
  *

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[PATCH 4.6 000/100] 4.6.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 074/100] serial: 8250_mid: recognize interrupt source in handler Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 070/100] tty/serial: atmel: fix hardware handshake selection Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 077/100] clk: bcm2835: add locking to pll*_on/off methods Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 069/100] TTY: n_gsm, fix false positive WARN_ON Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 055/100] usb: misc: usbtest: fix pattern tests for scatterlists. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 073/100] serial: 8250_mid: use proper bar for DNV platform Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 079/100] watchdog: sp5100_tco: properly check for new register layouts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 071/100] Fix OpenSSH pty regression on close Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 056/100] USB: leave LPM alone if possible when binding/unbinding interface drivers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 022/100] fscrypto/f2fs: allow fs-specific key prefix for fs encryption Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 076/100] locking,qspinlock: Fix spin_is_locked() and spin_unlock_wait() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 007/100] kvm: arm64: Fix EC field in inject_abt64 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 068/100] tty: vt, return error when con_startup fails Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 067/100] x86/cpufeature, x86/mm/pkeys: Fix broken compile-time disabling of pkeys Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 042/100] mei: amthif: discard not read messages Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 008/100] perf/x86/intel/uncore: Remove WARN_ON_ONCE in uncore_pci_probe Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 066/100] xen/x86: actually allocate legacy interrupts on PV guests Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 043/100] mei: bus: call mei_cl_read_start under device lock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 081/100] Fixing oops in callback path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 059/100] usb: host: xhci-rcar: Avoid long wait in xhci_reset() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 044/100] USB: serial: cp210x: fix hardware flow-control disable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 060/100] staging: comedi: das1800: fix possible NULL dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:30 +0200
  [PATCH 4.6 039/100] Bluetooth: vhci: purge unhandled skbs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:40 +0200
  [PATCH 4.6 038/100] Bluetooth: vhci: fix open_timeout vs. hdev race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:40 +0200
  [PATCH 4.6 016/100] ring-buffer: Prevent overflow of size in ring_buffer_resize() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:40 +0200
  [PATCH 4.6 033/100] mmc: sdhci-acpi: Remove MMC_CAP_BUS_WIDTH_TEST for Intel controllers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 037/100] mmc: sdhci-pci: Remove MMC_CAP_BUS_WIDTH_TEST for Intel controllers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 031/100] ACPI / PM: Export acpi_device_fix_up_power() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 027/100] irqchip/gic-v3: Configure all interrupts as non-secure Group-1 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 036/100] mmc: longer timeout for long read time quirk Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 020/100] clk: qcom: msm8916: Fix crypto clock flags Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 024/100] mfd: omap-usb-tll: Fix scheduling while atomic BUG Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 018/100] crypto: talitos - fix ahash algorithms registration Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 002/100] arm64: Ensure pmd_present() returns false after pmd_mknotpresent() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 025/100] Input: pwm-beeper - fix - scheduling while atomic Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 026/100] irqchip/gic: Ensure ordering between read of INTACK and shared data Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 030/100] mmc: mmc: Fix partition switch timeout for some eMMCs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
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  [PATCH 4.6 019/100] crypto: sun4i-ss - Replace spinlock_bh by spin_lock_irq{save|restore} Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 023/100] sched/loadavg: Fix loadavg artifacts on fully idle and on fully loaded systems Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 017/100] crypto: caam - fix caam_jr_alloc() ret code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  [PATCH 4.6 034/100] ACPI / osi: Fix an issue that acpi_osi=!* cannot disable ACPICA internal strings Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:50 +0200
  Re: [PATCH 4.6 000/100] 4.6.1-stable review Guenter Roeck <linux@roeck-us.net> - 2016-06-01 07:40 +0200
    Re: [PATCH 4.6 000/100] 4.6.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-01 18:20 +0200
      Re: [PATCH 4.6 000/100] 4.6.1-stable review "Xuetao Guan" <gxt@mprc.pku.edu.cn> - 2016-06-02 06:40 +0200
  Re: [PATCH 4.6 000/100] 4.6.1-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-06-01 16:30 +0200

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