| Message ID | 20190425223256.20270-1-fancer.lancer@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] usb: usb251xb: Lock i2c-bus segment the hub resides | expand |
On Fri, Apr 26, 2019 at 01:32:56AM +0300, Serge Semin wrote: Ahh, sorry. Forget about this email. I'll resend it with the valid In-Reply-To message-id. -Sergey > 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> > > --- > Changelog v2 > - Execute the check code only if GPIOLIB is enabled (reported by > a build robot). > > --- > drivers/usb/misc/usb251xb.c | 62 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 62 insertions(+) > > diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c > index 04684849d683..cdc80e8c2d8a 100644 > --- a/drivers/usb/misc/usb251xb.c > +++ b/drivers/usb/misc/usb251xb.c > @@ -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 +223,51 @@ static const struct usb251xb_data usb2517i_data = { > .product_str = "USB2517i", > }; > > +#ifdef CONFIG_GPIOLIB > +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; > +} > +#else > +static int usb251x_check_gpio_chip(struct usb251xb *hub) > +{ > + return 0; > +} > +#endif > + > 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 +275,8 @@ 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 +664,25 @@ 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); > -- > 2.21.0 >
diff --git a/drivers/usb/misc/usb251xb.c b/drivers/usb/misc/usb251xb.c index 04684849d683..cdc80e8c2d8a 100644 --- a/drivers/usb/misc/usb251xb.c +++ b/drivers/usb/misc/usb251xb.c @@ -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 +223,51 @@ static const struct usb251xb_data usb2517i_data = { .product_str = "USB2517i", }; +#ifdef CONFIG_GPIOLIB +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; +} +#else +static int usb251x_check_gpio_chip(struct usb251xb *hub) +{ + return 0; +} +#endif + 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 +275,8 @@ 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 +664,25 @@ 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);