On Tue, Jan 19, 2016 at 01:51:30AM +0000, Xie, Huawei wrote: > On 1/19/2016 9:34 AM, Yuanhan Liu wrote: > > On Mon, Jan 18, 2016 at 05:07:51PM +0000, Xie, Huawei wrote: > >> .On 1/15/2016 12:34 PM, Yuanhan Liu wrote: > >>> Modern (v1.0) virtio pci device defines several pci capabilities. > >>> Each cap has a configure structure corresponding to it, and the > >>> cap.bar and cap.offset fields tell us where to find it. > >>> > >> [snip] > >>> + > >>> +static inline void > >>> +io_write64_twopart(uint64_t val, uint32_t *lo, uint32_t *hi) > >>> +{ > >>> + io_write32((uint32_t)val, lo); > >>> + io_write32(val >> 32, hi); > >> Firstly your second iowrite32 doesn't do the conversion. > > Because it's not necessary. The first one is for retrieving the low 32 > > bits. > > I don't mean the shift operation, but the conversion from 64bit to 32bit. > Same applied to below.
It's more than a casting here: it's same as "val & (1<<32 - 1)", as stated above, to retrieve the low 32 bits. I know it still could work without it, but, hey, what's wrong to make it explicit? --yliu