[RFC][PATCH V3] axi: add AXI bus driver

Rafał Miłecki zajec5 at gmail.com
Mon Apr 11 18:12:47 EDT 2011

2011/4/11 Greg KH <greg at kroah.com>:
> On Mon, Apr 11, 2011 at 11:36:39PM +0200, Rafał Miłecki wrote:
>> 2011/4/11 Greg KH <greg at kroah.com>:
>> > Please read the documentation for how to do this properly.  I find it
>> > really hard to believe that you wrote that comment instead of putting in
>> > the 2 lines of code required for this function.
>> >
>> > Especially as-it-is, your code does not work properly and leaks memory
>> > badly.  Why would you do that on purpose?
>> I tried to read some documentation about this.
>> 1) driver-mode/device.txt says only that:
>> > Callback to free the device after all references have
>> > gone away. This should be set by the allocator of the
>> > device (i.e. the bus driver that discovered the device).
>> I *really* do not know how my driver should "free" core on AXI bus.
> The structure that you have created, added to the bus, is now ready to
> have its memory freed.  So free it.
> This usually means something like:
>        struct my_obj = to_my_obj(dev);
>        kfree(my_obj);
> in the release function.

I register core->dev to the bus (I set core->dev.bus and
core->dev.parent, is that what you mean?). This core->dev is "struct
dev" embedded in "struct axi_device". By embedded I mean it is *not* a
pointer, I do not alloc it, it's part of the "struct axi_device".

>> 2) LDD3 says:
>> > The method is called when the last reference to the device is removed; it is called
>> > from the embedded kobject’s release method. All device structures registered with
>> > the core must have a release method, or the kernel prints out scary complaints.
>> Well, I do not register any structs for AXI core.
> Yes you did, otherwise you would have never seen that callback warning
> you that you needed a release function.

I was thinking about alloc, sorry, ignore this one.

>> 4) SSB in it's ssb_release_dev just calls kfree on struct that was
>> allocated when registering drivers. *I do not* allocate such a struct,
>> so I believe I do exactly the same memory leak as SSB does.
> Well someone allocated it, right?  Who did it?  If it wasn't you, where
> did that structure come from and why are you registering it on your bus?
>> Can you spend 2 more minues in addition to commenting my ideas and
>> help me with writing that 2 lines I missed? Where do I leak memory in
>> my driver? Which struct should I kfree?
> The structure that you wrap around 'struct device' for your bus.

As explained above, this I do not dynamically alloc this 'struct
device'. So is there really any memory leak?


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