RE: [PATCH v4 2/8] iommu/dma: Introduce generic helper to retrieve RMR info

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Joerg Roedel [mailto:joro@8bytes.org]
> Sent: 18 May 2021 09:50
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
> Cc: linux-arm-kernel@lists.infradead.org; linux-acpi@vger.kernel.org;
> iommu@lists.linux-foundation.org; Linuxarm <linuxarm@huawei.com>;
> lorenzo.pieralisi@arm.com; robin.murphy@arm.com; wanghuiqiang
> <wanghuiqiang@huawei.com>; Guohanjun (Hanjun Guo)
> <guohanjun@huawei.com>; steven.price@arm.com; Sami.Mujawar@arm.com;
> jon@solid-run.com; eric.auger@redhat.com; yangyicong
> <yangyicong@huawei.com>
> Subject: Re: [PATCH v4 2/8] iommu/dma: Introduce generic helper to retrieve
> RMR info
> 
> On Thu, May 13, 2021 at 02:45:44PM +0100, Shameer Kolothum wrote:
> > +/**
> > + * struct iommu_rmr - Reserved Memory Region details per IOMMU
> > + * @list: Linked list pointers to hold RMR region info
> > + * @base_address: base address of Reserved Memory Region
> > + * @length: length of memory region
> > + * @sid: associated stream id
> > + * @flags: flags that apply to the RMR node
> > + */
> > +struct iommu_rmr {
> > +	struct list_head	list;
> > +	phys_addr_t		base_address;
> > +	u64			length;
> > +	u32			sid;
> > +	u32			flags;
> > +};
> > +
> > +/* RMR Remap permitted */
> > +#define IOMMU_RMR_REMAP_PERMITTED	(1 << 0)
> > +
> 
> This struct has lots of overlap with 'struct iommu_resv_region'. Any
> reason the existing struct can't be used here?
> 

Hmm..main reason is "sid". RMRs are associated with stream ids and
that is used to install bypass STEs/SMRs in SMMU drivers and also to check
whether a dev has any RMR regions associated with it.

I think we could add sid/dev_id to 'struct iommu_resv_region', and modify
iommu_alloc_resv_region() accordingly. That can get rid of the above struct
and iommu_dma_alloc_rmr() fn. Not sure this will complicate things as 
the dev_id is only valid for RMR reservation region cases. 

Please let me know your thoughts.

Thanks,
Shameer




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