RE: [PATCH] [net-next] net: hns3: add IOMMU_SUPPORT dependency

[Salil Mehta]

HI Robin,

>  From: Robin Murphy <robin.murphy@xxxxxxx>
>  Sent: Monday, November 4, 2024 10:29 AM
>  To: Arnd Bergmann <arnd@xxxxxxxxxx>; shenjian (K)
>  <shenjian15@xxxxxxxxxx>; Salil Mehta <salil.mehta@xxxxxxxxxx>
>  Cc: Arnd Bergmann <arnd@xxxxxxxx>; Will Deacon <will@xxxxxxxxxx>;
>  Joerg Roedel <jroedel@xxxxxxx>; iommu@xxxxxxxxxxxxxxx; Andrew Lunn
>  <andrew+netdev@xxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>; Eric
>  Dumazet <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
>  Paolo Abeni <pabeni@xxxxxxxxxx>; shaojijie <shaojijie@xxxxxxxxxx>;
>  wangpeiyang <wangpeiyang1@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx;
>  linux-kernel@xxxxxxxxxxxxxxx
>  Subject: Re: [PATCH] [net-next] net: hns3: add IOMMU_SUPPORT
>  dependency
>  
>  On 2024-11-04 8:21 am, Arnd Bergmann wrote:
>  > From: Arnd Bergmann <arnd@xxxxxxxx>
>  >
>  > The hns3 driver started filling iommu_iotlb_gather structures itself,
>  > which requires CONFIG_IOMMU_SUPPORT is enabled:
>  >
>  > drivers/net/ethernet/hisilicon/hns3/hns3_enet.c: In function
>  'hns3_dma_map_sync':
>  > drivers/net/ethernet/hisilicon/hns3/hns3_enet.c:395:14: error: 'struct
>  iommu_iotlb_gather' has no member named 'start'
>  >    395 |  iotlb_gather.start = iova;
>  >        |              ^
>  > drivers/net/ethernet/hisilicon/hns3/hns3_enet.c:396:14: error: 'struct
>  iommu_iotlb_gather' has no member named 'end'
>  >    396 |  iotlb_gather.end = iova + granule - 1;
>  >        |              ^
>  > drivers/net/ethernet/hisilicon/hns3/hns3_enet.c:397:14: error: 'struct
>  iommu_iotlb_gather' has no member named 'pgsize'
>  >    397 |  iotlb_gather.pgsize = granule;
>  >        |              ^
>  >
>  > Add a Kconfig dependency to make it build in random configurations.
>  >
>  > Cc: Will Deacon <will@xxxxxxxxxx>
>  > Cc: Joerg Roedel <jroedel@xxxxxxx>
>  > Cc: Robin Murphy <robin.murphy@xxxxxxx>
>  > Cc: iommu@xxxxxxxxxxxxxxx
>  > Fixes: f2c14899caba ("net: hns3: add sync command to sync io-pgtable")
>  > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>  > ---
>  > I noticed that no other driver does this, so it would be good to have
>  > a confirmation from the iommu maintainers that this is how the
>  > interface and the dependency is intended to be used.
>  
>  WTF is that patch doing!? No, random device drivers should absolutely not
>  be poking into IOMMU driver internals, this is egregiously wrong and the
>  correct action is to drop it entirely.


Absolutely agree with it. Sorry I haven't been in touch for quite some time. Let
me catch the whole story.  Feel free to drop this patch.

Thanks
Salil.

>  
>  Thanks,
>  Robin.
>  
>  > ---
>  >   drivers/net/ethernet/hisilicon/Kconfig | 1 +
>  >   1 file changed, 1 insertion(+)
>  >
>  > diff --git a/drivers/net/ethernet/hisilicon/Kconfig
>  > b/drivers/net/ethernet/hisilicon/Kconfig
>  > index 65302c41bfb1..790efc8d2de6 100644
>  > --- a/drivers/net/ethernet/hisilicon/Kconfig
>  > +++ b/drivers/net/ethernet/hisilicon/Kconfig
>  > @@ -91,6 +91,7 @@ config HNS_ENET
>  >   config HNS3
>  >   	tristate "Hisilicon Network Subsystem Support HNS3 (Framework)"
>  >   	depends on PCI
>  > +	depends on IOMMU_SUPPORT
>  >   	select NET_DEVLINK
>  >   	select PAGE_POOL
>  >   	help
>