On Sun, Mar 08, 2020 at 07:22:07PM +0000, Malcolm Priestley wrote: > >>> */ > >>> #undef __NO_VERSION__ > >>> > >>> +#include <linux/bits.h> > >>> #include <linux/etherdevice.h> > >>> #include <linux/file.h> > >>> #include "device.h" > >>> @@ -802,8 +803,7 @@ static u64 vnt_prepare_multicast(struct ieee80211_hw *hw, > >>> > >>> netdev_hw_addr_list_for_each(ha, mc_list) { > >>> bit_nr = ether_crc(ETH_ALEN, ha->addr) >> 26; > >>> - > >>> - mc_filter |= 1ULL << (bit_nr & 0x3f); > >>> + mc_filter |= BIT_ULL(bit_nr); > >> > >> Are you sure this does the same thing? You are not masking off bit_nr > >> anymore, why not? > > > > My reasons are exposed below: > > > > The ether_crc function returns an u32 type (unsigned of 32 bits). Then the right > > shift operand discards the 26 lsb bits (the bits shifted off the right side are > > discarded). The 6 msb bits of the u32 returned by the ether_crc function are > > positioned in bit 5 to bit 0 of the variable bit_nr. Due to the right shift > > happens over an unsigned type, the 26 new bits added on the left side will be 0. > > > > In summary, after the right bit shift operation we obtain in the variable bit_nr > > (unsigned of 32 bits) the value represented by the 6 msb bits of the value > > returned by the ether_crc function. So, only the 6 lsb bits of the variable > > bit_nr are important. The 26 msb bits of this variable are 0. > > > > In this situation, the "and" operation with the mask 0x3f (mask of 6 lsb bits) > > is unnecessary due to its purpose is to reset (set to 0 value) the 26 msb bits > > that are yet 0. > > The mask is only there out of legacy originally it was 31(0x1f) and the > bit_nr spread across two mc_filter u32 arrays. > > The mask is not needed now it is u64. > > The patch is fine. Ok, then the changelog needs to be fixed up to explain all of this and resent. thanks, greg k-h _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel