Re: [PATCH 2/4] remoteproc: introduce version element into resource type field

[Suman Anna]

On 5/21/20 2:41 PM, Bjorn Andersson wrote:
> On Thu 21 May 12:29 PDT 2020, Suman Anna wrote:
>
> > On 5/21/20 2:21 PM, Bjorn Andersson wrote:
> > > On Thu 21 May 12:06 PDT 2020, Suman Anna wrote:
> > >
> > > > Hi Bjorn,
> > > >
> > > > On 5/21/20 12:54 PM, Bjorn Andersson wrote:
> > > > > On Wed 25 Mar 13:46 PDT 2020, Suman Anna wrote:
> > > > >
> > > > > > The current remoteproc core has supported only 32-bit remote
> > > > > > processors and as such some of the current resource structures
> > > > > > may not scale well for 64-bit remote processors, and would
> > > > > > require new versions of resource types. Each resource is currently
> > > > > > identified by a 32-bit type field. Introduce the concept of version
> > > > > > for these resource types by overloading this 32-bit type field
> > > > > > into two 16-bit version and type fields with the existing resources
> > > > > > behaving as version 0 thereby providing backward compatibility.
> > > > > >
> > > > > > The version field is passed as an additional argument to each of
> > > > > > the handler functions, and all the existing handlers are updated
> > > > > > accordingly. Each specific handler will be updated on a need basis
> > > > > > when a new version of the resource type is added.
> > > > >
> > > > > I really would prefer that we add additional types for the new
> > > > > structures, neither side will be compatible with new versions without
> > > > > enhancements to their respective implementations anyways.
> > > >
> > > > OK.
> > > >
> > > > > > An alternate way would be to introduce the new types as completely
> > > > > > new resource types which would require additional customization of
> > > > > > the resource handlers based on the 32-bit or 64-bit mode of a remote
> > > > > > processor, and introduction of an additional mode flag to the rproc
> > > > > > structure.
> > > > >
> > > > > What would this "mode" indicate? If it's version 0 or 1?
> > > >
> > > > No, for indicating if the remoteproc is 32-bit or 64-bit and adjust the
> > > > loading handlers if the resource types need to be segregated accordingly.
> > >
> > > Sorry, I think I'm misunderstanding something. Wouldn't your 64-bit
> > > remote processor need different firmware from your 32-bit processor
> > > anyways, if you want to support the wider resource? And you would pack
> > > your firmware with the appropriate resource types?
> >
> > Yes, that's correct.
> >
> > > Afaict the bit width of your remote processor, busses or memory is
> > > unrelated to the choice of number of bits used to express things in the
> > > resource table.
> >
> > I would have to add the new resource type to the loading_handlers right, so
> > it is a question of whether we want to impose any restrictions in remoteproc
> > core or not from supporting a certain resource type (eg: I don't expect
> > RSC_TRACE entries on 64-bit processors).
>
> Right, but either you add support for new resource types to the
> loading_handlers, or you add the version checks within each handler,
> either way you will have to do some work to be compatible with new
> versions.
>
> Regarding what resources would be fit for a 64-bit processor probably
> relates to many things, in particular the question of what we actually
> mean when we say that a coprocessor is 64-bit. So I don't really see a
> need for the remoteproc core to prevent someone to design their
> system/firmware to have a 64-bit CPU being passed 32-bit addresses.

OK. In general, I have seen firmware developers get confused w.r.t the 
resource types, that's why I was inclined to go with the restrictive 
checking. Anyway, will rework the support as per the comments.

regards
Suman