| Message ID | 20190426104650.30240-1-fancer.lancer@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] usb: usb251xb: Lock i2c-bus segment the hub resides | expand |
On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > 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> I signed off on this? Where? When? never add a s-o-b line that you did not create, that implies a legal agreement. greg k-h
On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > 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> > > I signed off on this? Where? When? > > never add a s-o-b line that you did not create, that implies a legal > agreement. > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, since you already added the first version of this into linux-next tree. But apparently copy-pasted and left as is... -Sergey > greg k-h
On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > 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> > > > > I signed off on this? Where? When? > > > > never add a s-o-b line that you did not create, that implies a legal > > agreement. > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > since you already added the first version of this into linux-next tree. But > apparently copy-pasted and left as is... If I have already applied a patch, I can't apply it again (or a different version.) You need to send a fix-up patch for the reported issue, not a whole new one as I can not go back in time and rewrite history. thanks, greg k-h
On Sat, Apr 27, 2019 at 09:32:00AM +0200, Greg Kroah-Hartman wrote: > On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > > 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> > > > > > > I signed off on this? Where? When? > > > > > > never add a s-o-b line that you did not create, that implies a legal > > > agreement. > > > > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > > since you already added the first version of this into linux-next tree. But > > apparently copy-pasted and left as is... > > If I have already applied a patch, I can't apply it again (or a > different version.) You need to send a fix-up patch for the reported > issue, not a whole new one as I can not go back in time and rewrite > history. > > thanks, > > greg k-h Ok. Should I send it in reply to this patch or as a completely separate one? -Sergey
On Sat, Apr 27, 2019 at 10:39:41AM +0300, Serge Semin wrote: > On Sat, Apr 27, 2019 at 09:32:00AM +0200, Greg Kroah-Hartman wrote: > > On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > > > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > > > 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> > > > > > > > > I signed off on this? Where? When? > > > > > > > > never add a s-o-b line that you did not create, that implies a legal > > > > agreement. > > > > > > > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > > > since you already added the first version of this into linux-next tree. But > > > apparently copy-pasted and left as is... > > > > If I have already applied a patch, I can't apply it again (or a > > different version.) You need to send a fix-up patch for the reported > > issue, not a whole new one as I can not go back in time and rewrite > > history. > > > > thanks, > > > > greg k-h > > Ok. Should I send it in reply to this patch or as a completely separate one? A separate one.
On Sat, Apr 27, 2019 at 09:53:23AM +0200, Greg Kroah-Hartman wrote: > On Sat, Apr 27, 2019 at 10:39:41AM +0300, Serge Semin wrote: > > On Sat, Apr 27, 2019 at 09:32:00AM +0200, Greg Kroah-Hartman wrote: > > > On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > > > > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > > > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > > > > 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> > > > > > > > > > > I signed off on this? Where? When? > > > > > > > > > > never add a s-o-b line that you did not create, that implies a legal > > > > > agreement. > > > > > > > > > > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > > > > since you already added the first version of this into linux-next tree. But > > > > apparently copy-pasted and left as is... > > > > > > If I have already applied a patch, I can't apply it again (or a > > > different version.) You need to send a fix-up patch for the reported > > > issue, not a whole new one as I can not go back in time and rewrite > > > history. > > > > > > thanks, > > > > > > greg k-h > > > > Ok. Should I send it in reply to this patch or as a completely separate one? > > A separate one. Just did this. Two more questions. Is there any online service or ready-to-use configs-gen-script to build patchsets locally with various kernel configs before sending them for review? By using this I'd most likely prevent such unfortunate mistakes in future patches. I suppose the situation like this isn't unique, and there are other patches submitted with possible compilation problems. In this case seeing the linux-next will be eventually integrated into the linux-stable, then at the point of those patches the kernel source code will be build-broken corresponding config. In this case wouldn't it be better to have some rebasable branch with build robot service and fix the problematic patches in-place instead of apply an incrementing commits? This also would keep the source code cleaner at that particular commits. -Sergey
On Sat, Apr 27, 2019 at 12:31:11PM +0300, Serge Semin wrote: > On Sat, Apr 27, 2019 at 09:53:23AM +0200, Greg Kroah-Hartman wrote: > > On Sat, Apr 27, 2019 at 10:39:41AM +0300, Serge Semin wrote: > > > On Sat, Apr 27, 2019 at 09:32:00AM +0200, Greg Kroah-Hartman wrote: > > > > On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > > > > > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > > > > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > > > > > 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> > > > > > > > > > > > > I signed off on this? Where? When? > > > > > > > > > > > > never add a s-o-b line that you did not create, that implies a legal > > > > > > agreement. > > > > > > > > > > > > > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > > > > > since you already added the first version of this into linux-next tree. But > > > > > apparently copy-pasted and left as is... > > > > > > > > If I have already applied a patch, I can't apply it again (or a > > > > different version.) You need to send a fix-up patch for the reported > > > > issue, not a whole new one as I can not go back in time and rewrite > > > > history. > > > > > > > > thanks, > > > > > > > > greg k-h > > > > > > Ok. Should I send it in reply to this patch or as a completely separate one? > > > > A separate one. > > Just did this. > > Two more questions. > > Is there any online service or ready-to-use configs-gen-script to build > patchsets locally with various kernel configs before sending them for review? > By using this I'd most likely prevent such unfortunate mistakes in future > patches. 'make allmodconfig' works for me. Also, the 0-day bot sometimes will test patches sent to the mailing list before they are applied, but that doesn't always work. > I suppose the situation like this isn't unique, and there are other patches > submitted with possible compilation problems. In this case seeing the linux-next > will be eventually integrated into the linux-stable, then at the point of those > patches the kernel source code will be build-broken corresponding config. > In this case wouldn't it be better to have some rebasable branch with build > robot service and fix the problematic patches in-place instead of > apply an incrementing commits? This also would keep the source code cleaner > at that particular commits. As this passed the first round of 0-day testing in my rebasable branch, I assumed it was good enough. But later testing found that not to be the case, which is pretty rare. And I can't have public trees that are rebasable as people work off of them, so we can just live with fixing this up. thanks, greg k-h
On Sat, Apr 27, 2019 at 12:45:00PM +0200, Greg Kroah-Hartman wrote: > On Sat, Apr 27, 2019 at 12:31:11PM +0300, Serge Semin wrote: > > On Sat, Apr 27, 2019 at 09:53:23AM +0200, Greg Kroah-Hartman wrote: > > > On Sat, Apr 27, 2019 at 10:39:41AM +0300, Serge Semin wrote: > > > > On Sat, Apr 27, 2019 at 09:32:00AM +0200, Greg Kroah-Hartman wrote: > > > > > On Sat, Apr 27, 2019 at 10:10:27AM +0300, Serge Semin wrote: > > > > > > On Sat, Apr 27, 2019 at 09:00:42AM +0200, Greg Kroah-Hartman wrote: > > > > > > > On Fri, Apr 26, 2019 at 01:46:50PM +0300, Serge Semin wrote: > > > > > > > > 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> > > > > > > > > > > > > > > I signed off on this? Where? When? > > > > > > > > > > > > > > never add a s-o-b line that you did not create, that implies a legal > > > > > > > agreement. > > > > > > > > > > > > > > > > > > > Ah, shit. Sorry. I should have added Acked-by. That's what I was going to do, > > > > > > since you already added the first version of this into linux-next tree. But > > > > > > apparently copy-pasted and left as is... > > > > > > > > > > If I have already applied a patch, I can't apply it again (or a > > > > > different version.) You need to send a fix-up patch for the reported > > > > > issue, not a whole new one as I can not go back in time and rewrite > > > > > history. > > > > > > > > > > thanks, > > > > > > > > > > greg k-h > > > > > > > > Ok. Should I send it in reply to this patch or as a completely separate one? > > > > > > A separate one. > > > > Just did this. > > > > Two more questions. > > > > Is there any online service or ready-to-use configs-gen-script to build > > patchsets locally with various kernel configs before sending them for review? > > By using this I'd most likely prevent such unfortunate mistakes in future > > patches. > > 'make allmodconfig' works for me. Also, the 0-day bot sometimes will > test patches sent to the mailing list before they are applied, but that > doesn't always work. > > > I suppose the situation like this isn't unique, and there are other patches > > submitted with possible compilation problems. In this case seeing the linux-next > > will be eventually integrated into the linux-stable, then at the point of those > > patches the kernel source code will be build-broken corresponding config. > > In this case wouldn't it be better to have some rebasable branch with build > > robot service and fix the problematic patches in-place instead of > > apply an incrementing commits? This also would keep the source code cleaner > > at that particular commits. > > As this passed the first round of 0-day testing in my rebasable branch, > I assumed it was good enough. But later testing found that not to be > the case, which is pretty rare. And I can't have public trees that are > rebasable as people work off of them, so we can just live with fixing > this up. > > thanks, > > greg k-h Ok. Thanks for clarification. Next time I'll use the allmodconfig for a generic build-test and, as there aren't other way, try to anticipate a possible configs disabling issues. -Sergey
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);