linux-kernel - Re: Help with dma on PCI driver

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Message-ID: <AANLkTimkss168HfsPtJPpF1MiYAbHty3csW=R10P+=JA@mail.gmail.com>
Date:	Wed, 30 Mar 2011 13:11:40 -0300
From:	Luis Rossi <luisf.rossi@...il.com>
To:	Jonathan Corbet <corbet@....net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Help with dma on PCI driver

Thank you for your answer

Sorry for the code. I am not a kernel developer, i am a hardware
engineer, but i need to test a system i am designing. Most of the code
wasnt writen by me. I got it from another guy, the part that i wrote
so far was the one related to pci_alloc_constants. I will remake the
whole code soon to make it more readable. I was just testing some
concepts with it. I am trying to learn how to write  a driver based on
LDD3 and Linux Essential, but i was having a hard time. For now i
could find my problem. It was a dumb mistake and not realated to
kernel development. I forgot to allocate my structure.... so it was a
pointer to nothing.. But as you pointed me some problems.. just to
make sure.. should i stop the inti function on the device register,
and make all the rest inside probe? It makes a lot of sense as the
rest should be called just if the device is connected...

Thank you!!

On Wed, Mar 30, 2011 at 12:23 PM, Jonathan Corbet <corbet@....net> wrote:
>
> On Wed, 30 Mar 2011 07:07:32 -0300
> Luis Filipe Rossi <luisf.rossi@...il.com> wrote:
>
> > I am developing a driver for a custom PCI board. I am following the
> > example on Essential Linux Device Drivers, but when i am calling the
> > pci_alloc_consitent i get the following error:
> > Mar 29 15:18:42 luis-desktop kernel: [ 4520.075823] BUG: unable to
> > handle kernel NULL pointer dereference at 00000004
>
> Your source was horribly mangled, which is likely to reduce the number of
> responses you get.  I've not had the time to look at it in great detail,
> but I will say that the assumption that the PCI device is already probed
> and registered immediately after the pci_register_driver() call is
> dangerous at best.  Things like dma_descriptor_setup() should be called in
> your probe routine (or even later, when you actually need the buffer)
> rather than in your module init function.
>
> There's a lot of other issues with this driver, but that's the one I would
> look first at for the resolution of this particular crash.
>
> jon

--
Luís Filipe Rossi
Electrical Engineer
Biomechatronics Lab. / Grupo de Sensores Integráveis e Sistemas
Escola Politécnica
Universidade de São Paulo
Cel. +55 (11) 7662-9234
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