Re: [RFC 1/2] vhost: IFC VF hardware operation layer

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On 2019/10/22 上午12:31, Simon Horman wrote:
On Mon, Oct 21, 2019 at 05:55:33PM +0800, Zhu, Lingshan wrote:
On 10/16/2019 5:53 PM, Simon Horman wrote:
Hi Zhu,

thanks for your patch.

On Wed, Oct 16, 2019 at 09:10:40AM +0800, Zhu Lingshan wrote:
...

+static void ifcvf_read_dev_config(struct ifcvf_hw *hw, u64 offset,
+		       void *dst, int length)
+{
+	int i;
+	u8 *p;
+	u8 old_gen, new_gen;
+
+	do {
+		old_gen = ioread8(&hw->common_cfg->config_generation);
+
+		p = dst;
+		for (i = 0; i < length; i++)
+			*p++ = ioread8((u8 *)hw->dev_cfg + offset + i);
+
+		new_gen = ioread8(&hw->common_cfg->config_generation);
+	} while (old_gen != new_gen);
Would it be wise to limit the number of iterations of the loop above?
Thanks but I don't quite get it. This is used to make sure the function
would get the latest config.
I am worried about the possibility that it will loop forever.
Could that happen?

...


My understanding is that the function here is similar to virtio config generation [1]. So this can only happen for a buggy hardware.

Thanks

[1] https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html Section 2.4.1



+static void io_write64_twopart(u64 val, u32 *lo, u32 *hi)
+{
+	iowrite32(val & ((1ULL << 32) - 1), lo);
+	iowrite32(val >> 32, hi);
+}
I see this macro is also in virtio_pci_modern.c

Assuming lo and hi aren't guaranteed to be sequential
and thus iowrite64_hi_lo() cannot be used perhaps
it would be good to add a common helper somewhere.
Thanks, I will try after this IFC patchwork, I will cc you.
Thanks.

...





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