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Date: Tue, 19 Jan 2016 10:46:03 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: "Xie, Huawei" <huawei.xie@intel.com>
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Subject: Re: [dpdk-dev] [PATCH v4 7/8] virtio: add 1.0 support
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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