The platform firmware "location" data is used to find port peer
relationships. But firmware is an unreliable source. Errors in ACPI
tables can lead to missing or wrong peer relationships. Debugging
this is currently hard.
Exporting the location attribute makes it easier to spot mismatches
between the firmware data and the real world.
Signed-off-by: Bjørn Mork <bjorn@xxxxxxx>
---
This patch got stuck in one of my debugging branches. It proved very
useful to me while trying to figure out why the "peer" link was useless
on a specific host. And if it was useful to me once, then maybe it will
be to someone else as well...
tl;dr; The full use case for anyone interested:
Some current LTE modems with USB3 SS support come with a bootloader
supporting USB2 only. The application and bootloader modes are provided
by different softwares running on the modem (which of course is just
another Linux system with a UDC). None of the descriptors are therefore
guaranteed to be identical, or even similar.
Doing a firmware upgrade of such a device involves
- some preparation in application mode (USB3),
- rebooting into bootloader mode (USB2), and
- finally booting into the upgraded application firmware (USB3) to verify
the upgrade.
The firmware upgrade tool should make sure it talks to the same physical
device in all three phases. The only semi-reliable way to do that is to
look for "new" devices in the expected mode, connected to the same physical
USB port. But the locical port will change due to the USB2/3 switch, and
all we are left with is the "peer" link. Which can, and do, fail due to
buggy ACPI tables.
This patch won't solve that problem, but it makes it a lot easier to
detect.
Documentation/ABI/testing/sysfs-bus-usb | 15 ++++++++++++---
drivers/usb/core/port.c | 9 +++++++++
2 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 0bd731cbb50c..738bcccc420d 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -173,14 +173,14 @@ Description:
The file will be present for all speeds of USB devices, and will
always read "no" for USB 1.1 and USB 2.0 devices.
-What: /sys/bus/usb/devices/.../(hub interface)/portX
+What: /sys/bus/usb/devices/.../(hub interface)/usbY-portX
Date: August 2012
Contact: Lan Tianyu <tianyu.lan@xxxxxxxxx>
Description:
The /sys/bus/usb/devices/.../(hub interface)/portX
is usb port device's sysfs directory.
-What: /sys/bus/usb/devices/.../(hub interface)/portX/connect_type
+What: /sys/bus/usb/devices/.../(hub interface)/usbY-portX/connect_type
Date: January 2013
Contact: Lan Tianyu <tianyu.lan@xxxxxxxxx>
Description:
@@ -189,7 +189,16 @@ Description:
The file will read "hotplug", "wired" and "not used" if the
information is available, and "unknown" otherwise.
-What: /sys/bus/usb/devices/.../(hub interface)/portX/usb3_lpm_permit
+What: /sys/bus/usb/devices/.../(hub interface)/usbY-portX/location
+Date: October 2018
+Contact: Bjørn Mork <bjorn@xxxxxxx>
+Description:
+ Some platforms provide usb port physical location through
+ firmware. This is used by the kernel to pair up logical ports
+ mapping to the same physical connector. The attribute exposes the
+ raw location value as a hex integer.
+
+What: /sys/bus/usb/devices/.../(hub interface)/usbY-portX/usb3_lpm_permit
Date: November 2015
Contact: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Description:
diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index 1a01e9ad3804..baa35ba410b6 100644
--- a/drivers/usb/core/port.c
+++ b/drivers/usb/core/port.c
@@ -16,6 +16,15 @@ static int usb_port_block_power_off;
static const struct attribute_group *port_dev_group[];
+static ssize_t location_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct usb_port *port_dev = to_usb_port(dev);
+
+ return sprintf(buf, "0x%08x\n", port_dev->location);
+}
+static DEVICE_ATTR_RO(location);
+
static ssize_t connect_type_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
--
2.11.0
