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

[Zhu Lingshan <lingshan.zhu@linux.intel.com>]

On 10/22/2019 9:32 AM, Jason Wang wrote:
>
> 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
Yes!
>
>
>>
>>>>> +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.
>>
>> ...
>