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usb: usb251xb: Lock i2c-bus segment the hub resides

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SMBus slave configuration is activated by CFG_SEL[1:0]=0x1 pins
state. This is the mode the hub is supposed to be to let this driver
work correctly. But a race condition might happen right after reset
is cleared due to CFG_SEL[0] pin being multiplexed with SMBus SCL
function. In case if the reset pin is handled by a i2c GPIO expander,
which is also placed at the same i2c-bus segment as the usb251x
SMB-interface connected to, then the hub reset clearance might
cause the CFG_SEL[0] being latched in unpredictable state. So
sometimes the hub configuration mode might be 0x1 (as expected),
but sometimes being 0x0, which doesn't imply to have the hub SMBus-slave
interface activated and consequently causes this driver failure.

In order to fix the problem we must make sure the GPIO-reset chip doesn't
reside the same i2c-bus segment as the SMBus-interface of the hub. If
it doesn't, we can safely block the segment for the time the reset is
cleared to prevent anyone generating a traffic at the i2c-bus SCL lane
connected to the CFG_SEL[0] pin. But if it does, nothing we can do, so
just return an error. If we locked the i2c-bus segment and tried to
communicate with the GPIO-expander, it would cause a deadlock. If we didn't
lock the i2c-bus segment, it would randomly cause the CFG_SEL[0] bit flip.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Serge Semin 2019-04-24 17:49:14 +03:00 committed by Greg Kroah-Hartman
parent 77a4946516
commit 6e3c8beb4f
1 changed files with 55 additions and 0 deletions
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55
drivers/usb/misc/usb251xb.c
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@ -12,6 +12,7 @@
#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/gpio/driver.h>
#include <linux/i2c.h>
#include <linux/module.h>
#include <linux/nls.h>
@ -222,11 +223,44 @@ static const struct usb251xb_data usb2517i_data = {
.product_str = "USB2517i",
};
static int usb251xb_check_dev_children(struct device *dev, void *child)
{
if (dev->type == &i2c_adapter_type) {
return device_for_each_child(dev, child,
usb251xb_check_dev_children);
}
return (dev == child);
}
static int usb251x_check_gpio_chip(struct usb251xb *hub)
{
struct gpio_chip *gc = gpiod_to_chip(hub->gpio_reset);
struct i2c_adapter *adap = hub->i2c->adapter;
int ret;
if (!hub->gpio_reset)
return 0;
if (!gc)
return -EINVAL;
ret = usb251xb_check_dev_children(&adap->dev, gc->parent);
if (ret) {
dev_err(hub->dev, "Reset GPIO chip is at the same i2c-bus\n");
return -EINVAL;
}
return 0;
}
static void usb251xb_reset(struct usb251xb *hub, int state)
{
if (!hub->gpio_reset)
return;
i2c_lock_bus(hub->i2c->adapter, I2C_LOCK_SEGMENT);
gpiod_set_value_cansleep(hub->gpio_reset, state);
/* wait for hub recovery/stabilization */
@ -234,6 +268,8 @@ static void usb251xb_reset(struct usb251xb *hub, int state)
usleep_range(500, 750); /* >=500us at power on */
else
usleep_range(1, 10); /* >=1us at power down */
i2c_unlock_bus(hub->i2c->adapter, I2C_LOCK_SEGMENT);
}
static int usb251xb_connect(struct usb251xb *hub)
@ -621,6 +657,25 @@ static int usb251xb_probe(struct usb251xb *hub)
}
}
/*
* usb251x SMBus-slave SCL lane is muxed with CFG_SEL0 pin. So if anyone
* tries to work with the bus at the moment the hub reset is released,
* it may cause an invalid config being latched by usb251x. Particularly
* one of the config modes makes the hub loading a default registers
* value without SMBus-slave interface activation. If the hub
* accidentally gets this mode, this will cause the driver SMBus-
* functions failure. Normally we could just lock the SMBus-segment the
* hub i2c-interface resides for the device-specific reset timing. But
* the GPIO controller, which is used to handle the hub reset, might be
* placed at the same i2c-bus segment. In this case an error should be
* returned since we can't safely use the GPIO controller to clear the
* reset state (it may affect the hub configuration) and we can't lock
* the i2c-bus segment (it will cause a deadlock).
*/
err = usb251x_check_gpio_chip(hub);
if (err)
return err;
err = usb251xb_connect(hub);
if (err) {
dev_err(dev, "Failed to connect hub (%d)\n", err);