From: Giuseppe CAVALLARO <peppe.cavallaro@st•com>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org
Subject: Re: [PATCH] net: fix unaligned memory accesses in ASIX
Date: Thu, 26 Mar 2009 11:01:50 +0100 [thread overview]
Message-ID: <49CB528E.9060505@st.com> (raw)
In-Reply-To: <20090326.020018.26561577.davem@davemloft.net>
David Miller wrote:
> From: Giuseppe CAVALLARO <peppe.cavallaro@st•com>
> Date: Thu, 26 Mar 2009 09:40:13 +0100
>
>
>> Unfortunately, unaligned memory accesses seems to depend on the Asix HW
>> that packs several incoming frames.
>> So when these frames are 'unpacked' within the fix-up function, and
>> pushed to the upper layer, they can have a wrong alignment, indeed.
>> When no frame is packed all works fine and the IP never works with
>> unaligned addresses.
>> I think, the skb_reserve could actually help us, if this last scenario
>> generated misaligned accesses.
>> Please let me know if I'm missing something.
>>
>
> The unpacker is taking a set of packet(s) in a USB buffer
> and copying them into SKB's right? That code should be where
> the offset is checked in the child driver, and adjustments
> made as-needed.
>
> This code seems to call the downstream driver callback after
> the damage is done. I think it needs to ask the driver to
> look for and indicate the offset before the building of the
> SKB is performed.
>
I understand your point of view.
In any case, at first glance, I understand that the urb->transfer_buffer
directly points to the preallocated skb data.
These are filled by the HWs. I mean, the buffers are treated by the HW.
So I guess, the meaning of the rx_fixup functions is just to solve this
kind of situations.
In fact, each usb net driver has an own fixup code according to their HW
specifications.
Peppe
next prev parent reply other threads:[~2009-03-26 10:02 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-26 6:52 [PATCH] net: fix unaligned memory accesses in ASIX Giuseppe CAVALLARO
2009-03-26 8:08 ` David Miller
2009-03-26 8:40 ` Giuseppe CAVALLARO
2009-03-26 9:00 ` David Miller
2009-03-26 10:01 ` Giuseppe CAVALLARO [this message]
2009-04-15 10:14 ` David Miller
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