RE: Implementing IOMMU support for SDHCI

[Sai Pavan Boddu]

Hi Peter,

> -----Original Message-----
> From: Peter Maydell <address@hidden>
> Sent: Wednesday, February 26, 2020 9:59 PM
> To: Sai Pavan Boddu <address@hidden>
> Cc: address@hidden; QEMU Developers <address@hidden>;
> Edgar Iglesias <address@hidden>
> Subject: Re: Implementing IOMMU support for SDHCI
> 
> On Wed, 26 Feb 2020 at 12:38, Sai Pavan Boddu <address@hidden>
> wrote:
> >
> > Hi Poalo/Peter,
> >
> > We are trying to add SMMU support for dma's used in SD controller on
> ZynqMP boards. In order to do that we need a clean way to assign
> MemTxAttrs to each device(i.e all devices which connect to smmu) via
> "object_add_link_property/ object_set_link_property "  functions.
> >
> > But in order to do that, first we may need to convert MemTxAttrs as QOM
> object. I just need some feedback, if its advisable to do so ?
> 
> We create and throw around MemTxAttrs structs a lot, I don't think they're
> suitable to be QOM objects. I don't think you need it, anyway -- your problem
> is rather that the iommu doesn't get an opportunity to sit in the middle of
> transactions the way you'd like it to, and making MemTxAttrs a QOM object
> doesn't help address that.
[Sai Pavan Boddu] Our idea is to create dma helper function which can also pass 
the MemTxAttr i.e like 
dma_memory_rw_attr (AddressSpace *as, dma_addr_t addr,
                                     void *buf, dma_addr_t len,
                                     DMADirection dir,
                                     MemTxAttrs attr)
which needs to be used in sdhci,  with "AddressSpace *as" pointing to smmu.

I see we don’t need QOM variant of MemTxAttr for this functionality, but 
thought it would be good to use  " object_add_link_property/ 
object_set_link_property " to set the values from machine file's. I would drop 
this idea, and look for other options to set the attributes.

Regards,
Sai Pavan

> 
> thanks
> -- PMM