On Thu, 31 Mar 2022 17:33:03 +0200, Benson Leung wrote: > > Hi Takashi, > > On Thu, Mar 31, 2022 at 04:19:15PM +0200, Takashi Iwai wrote: > > On Thu, 31 Mar 2022 15:29:10 +0200, > > Takashi Iwai wrote: > > > > > > On Thu, 31 Mar 2022 11:45:47 +0200, > > > Takashi Iwai wrote: > > > > > > > > On Thu, 31 Mar 2022 11:34:38 +0200, > > > > Heikki Krogerus wrote: > > > > > > > > > > On Thu, Mar 31, 2022 at 11:28:20AM +0200, Takashi Iwai wrote: > > > > > > On Thu, 31 Mar 2022 11:25:43 +0200, > > > > > > Heikki Krogerus wrote: > > > > > > > > > > > > > > On Thu, Mar 31, 2022 at 11:12:55AM +0200, Takashi Iwai wrote: > > > > > > > > > > > - if (!strcmp(dev->driver->name, "i915") && > > > > > > > > > > > + if (dev->driver && !strcmp(dev->driver->name, "i915") && > > > > > > > > > > > > > > > > > > > > Can NULL dev->driver be really seen? I thought the components are > > > > > > > > > > added by the drivers, hence they ought to have the driver field set. > > > > > > > > > > But there can be corner cases I overlooked. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > thanks, > > > > > > > > > > > > > > > > > > > > Takashi > > > > > > > > > > > > > > > > > > Hi Takashi, > > > > > > > > > > > > > > > > > > When I try using component_add in a different driver (usb4 in my > > > > > > > > > case), I think dev->driver here is NULL because the i915 drivers do > > > > > > > > > not have their component master fully bound when this new component is > > > > > > > > > registered. When I test it, it seems to be causing a crash. > > > > > > > > > > > > > > > > Hm, from where component_add*() is called? Basically dev->driver must > > > > > > > > be already set before the corresponding driver gets bound at > > > > > > > > __driver_probe_deviec(). So, if the device is added to component from > > > > > > > > the corresponding driver's probe, dev->driver must be non-NULL. > > > > > > > > > > > > > > The code that declares a device as component does not have to be the > > > > > > > driver of that device. > > > > > > > > > > > > > > In our case the components are USB ports, and they are devices that > > > > > > > are actually never bind to any drivers: drivers/usb/core/port.c > > > > > > > > > > > > OK, that's what I wanted to know. It'd be helpful if it's more > > > > > > clearly mentioned in the commit log. > > > > > > > > > > Agree. > > > > > > > > > > > BTW, the same problem must be seen in MEI drivers, too. > > > > > > > > > > Wasn't there a patch for those too? I lost track... > > > > > > > > I don't know, I just checked the latest Linus tree. > > > > > > > > And, looking at the HD-audio code, I still wonder how NULL dev->driver > > > > can reach there. Is there any PCI device that is added to component > > > > without binding to a driver? We have dev_is_pci() check at the > > > > beginning, so non-PCI devices should bail out there... > > > > > > Further reading on, I'm really confused. How data=NULL can be passed > > > to this function? The data argument is the value passed from the > > > component_match_add_typed() call in HD-audio driver, hence it must be > > > always the snd_hdac_bus object. > > > > > > And, I guess the i915 string check can be omitted completely, at > > > least, for HD-audio driver. It already have a check of the parent of > > > the device and that should be enough. > > > > That said, something like below (supposing data NULL check being > > superfluous), instead. > > > > > > Takashi > > > > --- a/sound/hda/hdac_i915.c > > +++ b/sound/hda/hdac_i915.c > > @@ -102,18 +102,13 @@ static int i915_component_master_match(struct device *dev, int subcomponent, > > struct pci_dev *hdac_pci, *i915_pci; > > struct hdac_bus *bus = data; > > > > - if (!dev_is_pci(dev)) > > + if (subcomponent != I915_COMPONENT_AUDIO || !dev_is_pci(dev)) > > return 0; > > > > If I recall this bug correctly, it's not the usb port perse that is falling > through this !dev_is_pci(dev) check, it's actually the usb4-port in a new > proposed patch by Heikki and Mika to extend the usb type-c component to > encompass the usb4 specific pieces too. Is it possible usb4 ports are considered > pci devices, and that's how we got into this situation? Yes, that explains for one of two changes in the original patch. But why data==NULL check is needed is still unclear. > Also, a little more background information: This crash happens because in > our kernel configs, we config'd the usb4 driver as =y (built in) instead of > =m module, which meant that the usb4 port's driver was adding a component > likely much earlier than hdac_i915. Thanks, it's what I supposed, too. Takashi
