On 9/25/2013 8:57 PM, Alexey Brodkin wrote:
It's important that buffer descriptors are aligned in accordance to GMAC data bus width (32/64/128-bit). It's safe to align to 128-bit (16-bytes) for every bus width type.
If buffer descriptor is improperly aligned GMAC discards lower bits of provided address and as a result reads from improper location that doesn't match expected fields.
Commit ef76025a99247cdb8f927a2c9f15400678dfb599 "net: Multiple updates/enhancements to designware.c" introduced another structure member "link_printed" right before buffer descriptors while "padding" member was left untouched. This together with alignment of structure itself to 16-byte boundary forces buffer descriptoprs always to be 4-byte aligned that causes driver complete disfunction if GMAC bus width is 64 or 128-bit.
I have also faced this problem before. May be a better solution is to place all the struct and buffer declarations at the very start of dw_eth_dev structure (off-course with a comment that these should not be moved). It may avoid the problem in later modifications
Regards Vipin