.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. The conversion
is duplicated.

+}
+
+static void
+modern_read_dev_config(struct virtio_hw *hw, uint64_t offset,

here and there, size_t is more accurate for offset as we get it from
offsetof.

+		       void *dst, int length)
+{
+	int i;
+	uint8_t *p;
+	uint8_t old_gen, new_gen;
+
+	do {
+		old_gen = io_read8(&hw->common_cfg->config_generation);
+
+		p = dst;
+		for (i = 0;  i < length; i++)
+			*p++ = io_read8((uint8_t *)hw->dev_cfg + offset + i);
+
+		new_gen = io_read8(&hw->common_cfg->config_generation);
+	} while (old_gen != new_gen);
+}
+
+static void
+modern_write_dev_config(struct virtio_hw *hw, uint64_t offset,
+			const void *src, int length)
+{
+	int i;
+	const uint8_t *p = src;
+
+	for (i = 0;  i < length; i++)
+		io_write8(*p++, (uint8_t *)hw->dev_cfg + offset + i);
+}
+
+static uint64_t
+modern_get_features(struct virtio_hw *hw)
+{
+	uint32_t features_lo, features_hi;
+
+	io_write32(0, &hw->common_cfg->device_feature_select);
+	features_lo = io_read32(&hw->common_cfg->device_feature);
+
+	io_write32(1, &hw->common_cfg->device_feature_select);
+	features_hi = io_read32(&hw->common_cfg->device_feature);
+
+	return ((uint64_t)(features_hi) << 32) | features_lo;
+}
+
+static void
+modern_set_features(struct virtio_hw *hw, uint64_t features)
+{
+	io_write32(0, &hw->common_cfg->guest_feature_select);
+	io_write32(features & ((1ULL << 32) - 1),

again, duplicated conversion

+		&hw->common_cfg->guest_feature);
+
+	io_write32(1, &hw->common_cfg->guest_feature_select);

[snip]