On Tue, Jan 19, 2016 at 01:51:30AM +0000, Xie, Huawei wrote:

On 1/19/2016 9:34 AM, Yuanhan Liu wrote:

quoted

On Mon, Jan 18, 2016 at 05:07:51PM +0000, Xie, Huawei wrote:

quoted

.On 1/15/2016 12:34 PM, Yuanhan Liu wrote:

quoted

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]

quoted

+
+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