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

[Jijie Shao]

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@xxxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxxx>
> > > > Signed-off-by: Jian Shen <shenjian15@xxxxxxxxxx>
> > > > Signed-off-by: Jijie Shao <shaojijie@xxxxxxxxxx>
> > > 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.