Re: [PATCH V2 net 1/9] net: hns3: default enable tx bounce buffer when smmu enabled

[Jijie Shao <shaojijie@huawei.com>]

on 2024/10/25 0:04, Simon Horman wrote:
> On Thu, Oct 24, 2024 at 04:31:46PM +0800, Jijie Shao wrote:
>> on 2024/10/24 16:26, Paolo Abeni wrote:
>>> On 10/18/24 12:10, Jijie Shao wrote:
>>>> From: Peiyang Wang <wangpeiyang1@huawei.com>
>>>>
>>>> The SMMU engine on HIP09 chip has a hardware issue.
>>>> SMMU pagetable prefetch features may prefetch and use a invalid PTE
>>>> even the PTE is valid at that time. This will cause the device trigger
>>>> fake pagefaults. The solution is to avoid prefetching by adding a
>>>> SYNC command when smmu mapping a iova. But the performance of nic has a
>>>> sharp drop. Then we do this workaround, always enable tx bounce buffer,
>>>> avoid mapping/unmapping on TX path.
>>>>
>>>> This issue only affects HNS3, so we always enable
>>>> tx bounce buffer when smmu enabled to improve performance.
>>>>
>>>> Signed-off-by: Peiyang Wang <wangpeiyang1@huawei.com>
>>>> Signed-off-by: Jian Shen <shenjian15@huawei.com>
>>>> Signed-off-by: Jijie Shao <shaojijie@huawei.com>
>>> I'm sorry to nick pick on somewhat small details, but we really need a
>>> fixes tag here to make 110% clear is a bugfix. I guess it could be the
>>> commit introducing the support for the buggy H/W.
>>>
>>> Thanks,
>>>
>>> Paolo
>> I have a little doubt that this patch is about H/W problem,
>> so how can we write the the fixes tag?
> Hi Jijie,
>
> That is a good point. But the much point of the Fixes tag is to indicate how
> far back the fix should be backported. So I would say the ID of the patch
> where the user would have first seen this problem - possibly the patch that
> added the driver.

That's a good idea. Thank you.