In message <[EMAIL PROTECTED]>,David Miller writes:
>From: Christoph Hellwig <[EMAIL PROTECTED]>
>Date: Thu, 13 Jul 2006 22:36:16 +0200
>> - drivers/atm/{idt77252.c, nicstar.c}, drivers/usb/atm/usbatm.c:
>> These use private skb queues and do odd things. I can't see
>> any point for using dev_alloc_skb with it's additional headroom
>> reservation here.
as i recall, for simple rfc1483 encapsulation, the LLC/SNAP header of 8
bytes needs to be replaced by an ether header of 14 bytes. its likely
this is the reason dev_alloc_skb() is used. most of the other drivers
use atm_alloc_charge() which does a skb_reserve(), but these drivers
dont dma directly into a skb.
>Any of these cases that DMA into the skb allocated will need
>the headroom, as explained by the PowerPC folks.
this only works for "ordinary" ip traffic (which i admit is the most
common case). but since the nicstar/idt77252 devices have a peak
speed of 155Mb/s i doubt they would suffer much. considering they still
use virt_to_bus/bus_to_virt i would be a bit surprised if they worked
(atleast on ppc64). they can be simply converted to alloc_skb() and
manually skb_reserve() a little overhead.
usbatm should probably be converted to use atm_alloc_charge() since
the vcc is known at this point unlike the nicstar/idt77252 case.
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