Re: [PATCH net 4/4] net: hns3: default enable tx bounce buffer when smmu enabled

[Jijie Shao <shaojijie@huawei.com>]

on 2025/7/5 0:31, Simon Horman wrote:
> On Wed, Jul 02, 2025 at 09:09:01PM +0800, Jijie Shao wrote:
>> 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.
>>
>> Fixes: 295ba232a8c3 ("net: hns3: add device version to replace pci revision")
> The cited commit may be a pre-requisite for this patch
> to check HNAE3_DEVICE_VERSION_V3. But it seems to me that the problem
> being addressed existed before the cited commit. If so, I think a different
> Fixes tag is appropriate.
>
>> Signed-off-by: Jian Shen <shenjian15@huawei.com>
>> Signed-off-by: Jijie Shao <shaojijie@huawei.com>
>> ---
>>   .../net/ethernet/hisilicon/hns3/hns3_enet.c   | 31 +++++++++++++++++
>>   .../net/ethernet/hisilicon/hns3/hns3_enet.h   |  2 ++
>>   .../ethernet/hisilicon/hns3/hns3_ethtool.c    | 33 +++++++++++++++++++
> It seems to me that the hns3_ethtool.c changes a) are not a requirement
> for the work-around introduced by this patch and b) may introduce
> complex behaviour between the effect of ethtool copybreak settings
> and the enablement/non-enablement of the work-around.
>
> Would it be possible to make a more minimal fix for net, that
> omits the ethtool changes. And then follow-up with them for net-next
> once the fix is present there?

I will discuss your suggestion with my team.

Thanks
Jijie Shao