Messages in this thread | | | From | Lars Poeschel <> | Subject | Re: [PATCH v2 1/4] mfd: add viperboard driver | Date | Tue, 16 Oct 2012 11:43:19 +0200 |
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On Tuesday 16 October 2012 at 10:40:26, Lars-Peter Clausen wrote: > On 10/12/2012 04:34 PM, Lars Poeschel wrote: > > [...] > > +static void vprbrd_dev_release(struct device *dev) > > +{ > > + return; > > A empty release callback is usually a good indicator that something is > wrong. The release callback will be called once the last reference to the > device has been called, so the memory associated with the device should not > be freed before the release callback has been called, otherwise the memory > might be accessed after it has been freed... > > > +} > > + > > +static void vprbrd_free(struct vprbrd *dev) > > +{ > > + usb_put_dev(dev->usb_dev); > > + kfree(dev); > > ..., so this kfree should be moved from here to the release callback.
Thank you for catching that one!
> Btw. I'm wondering why is the extra platform device required? Can't you not > just use the usb device as the parent device for the mfd cells?
This is what I first did, but this does not work. You can read about my first thoughts why this is not working here: (To sum it up: The device is housed in an usb_device, not a platform_device and This usb_device has no mfd_cell member.)
https://lkml.org/lkml/2012/9/28/327
As I got a bit more deeper I also noticed, that mfd_add_devices (obviously) adds the devices "as childs" to the parent device. mfd_remove_devices then removes ALL "child" devices from the parent, not only those added by mfd_add_devices before. This does not work in the case of the usb parent device, because it has other childs that the usb layer added before (some endpoints and stuff). So I had to construct an "empty" (in sense of childs) mock platform_device between the usb and mfd.
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