Hi,
On a MIPS 32 Big endian system the netdev_sync_upper_features() function does
not work correctly.
It does not disbale bit 15 (NETIF_F_LRO, 0x0000000000008000), but 47
(NETIF_F_HW_TC, 0x0000800000000000).
The for_each_netdev_feature() macro is used to go over all netdev feature flags
and calls for_each_set_bit() with a u64.
This is the code:
#define for_each_netdev_feature(mask_addr, bit) \
for_each_set_bit(bit, (unsigned long *)mask_addr, NETDEV_FEATURE_COUNT)
https://elixir.bootlin.com/linux/v4.19-rc2/source/include/linux/netdev_features.h#L157
The for_each_set_bit() macro calls the find_first_bit() macro and works
directly on the bits in the memory
organized in 32 bit values in the generic implementation, see here:
https://elixir.bootlin.com/linux/v4.19-rc2/source/lib/find_bit.c#L102
On big endian systems the u64 value is stored in a different order in memory
compared to little endian systems.
When I execute this code:
netdev_features_t upper_disables = NETIF_F_UPPER_DISABLES;
printk("%s:%i: addr: 0x%llx, size: %i\n", __func__, __LINE__,
upper_disables, NETDEV_FEATURE_COUNT);
ret = find_first_bit((unsigned long *)&upper_disables,
NETDEV_FEATURE_COUNT);
printk("%s:%i: addr: 0x%llx, size: %i, ret: %li\n", __func__, __LINE__,
upper_disables, NETDEV_FEATURE_COUNT, ret);
I get this result:
[ 35.227140] netdev_sync_upper_features:6912: addr: 0x8000, size: 48
[ 35.233337] netdev_sync_upper_features:6914: addr: 0x8000, size: 48,
ret: 47
Expected would be a ret: 15.
As I understood the documentation for for_each_set_bit() this should find the
first bit in memory and not in a integer,
so for_each_netdev_feature() should not use for_each_set_bit().
I do not really know what a good fix would be, I could convert the feature
flags to little endian before calling for_each_netdev_feature(), would this be
ok?
Hauke
