[6-freebsd-12 PATCH 1/2] rtemsbsd/bus: Add PCI support to the nexus bus

Thu Mar 4 15:41:07 UTC 2021

On Thu, Mar 4, 2021 at 12:32 AM Chris Johns <chrisj at rtems.org> wrote:
>
> On 4/3/21 5:53 pm, Sebastian Huber wrote:
> > On 04/03/2021 00:18, Chris Johns wrote:
> >> On 3/3/21 7:48 pm, Sebastian Huber wrote:
> >>> On 03/03/2021 08:52, Chris Johns wrote:
> >>>> Then I hit minimum and some validation tests and they failed because I had
> >>>> removed bsp/default-initial-extension.h and I suppose it needs to come via
> >>>> bsp.h
> >>>> however it includes rtems.h because it needs to have access to
> >>>> rtems_fatal_source etc.
> >>>>
> >>>> It seems there is a lot of places that subtly depend on bsp.h and what it
> >>>> includes.
> >>>>
> >>>> I will chat to Joel tomorrow to figure out how this is to be resolved.
> >>>>
> >>>> Any suggestions?
> >>> The minimum requirement for bsp.h is to include:
> >>>
> >>> rtems.h
> >>>
> >>> bspopts.h
> >> It is news to me this is a requirement and I am unsure where it has come from.
> >> Has it been documented? The information you cut from my last post shows RTEMS is
> >> pretty clean and the number of issues are small so I am not sure this needs to
> >> happen.
> > This is what I figured out over the years.
>
> I think the ability to have them separated is healthy.
>
> >>
> >> These powerpc BSPs predate libbsd, they have legacy networking support and are
> >> important to RTEMS users.
> >>
> >> Your request to not including bsp.h because it includes rtems.h in a driver
> >> section of a third party package that needs specific BSP bus mapping information
> >> appear to conflict. The package needs low level BSP information but it cannot
> >> include bsp.h by definition now.
> >>
> >> What is now bugging me is the layering of rule upon rule mixed with defaults.
> >> The rules are complex and in places seem arbitrary. Let me write the rules out
> >> as I understand them:
> >>
> >> 1. The BSP header bsp.h is the access to BSP interfaces
> >>
> >> 2. The BSP header bsp.h must include rtems.h and bspopt.h
> >>
> >> 3. LibBSD generic bus handling must be inline for performance reasons
> >>
> >> 4. LibBSD generic bus handling assumes cache coherent memory by default
> >>
> >> 5. BSPs must register cache coherent memory if it does not meet rule 4
> >>
> >> 6. LibBSD generic bus handling defaults to a flat 1:1 full memory space
> >>     address map
> >>
> >> 7. LibBSD generic bus handling requires bsp/bus.h to provide BSP mappings
> >>     if it does not meet rule 6
> >>
> >> 8. A BSP provided bsp/bus.h cannot include rtems.h or any header that
> >>     includes rtems.h such as bsp.h. This special case is exempt from rule 1
> >>
> >> 9. RTEMS cannot change any header an existing BSP with bsp/bus.h
> >>     includes to include rtems.h or any header that has a dependent that
> >>     includes rtems.h
> >>
> >> <bleach> that is a lot of rules to swallow. An alternative set of rules is:
> >>
> >> 1. The BSP header bsp.h is the access to BSP interfaces
> >>
> >> 2. LibBSD generic bus handling must be inline for performance reasons
> >>
> >> 3. LibBSD generic bus handling requires a BSP provide suitable cache
> >>     coherent memory to the cache coherent memory allocator
> >>
> >> 4. LibBSD generic bus handling requires a BSP provide bsp/bus.h to
> >>     provide BSP IO mappings
> >>
> >> The second set of rules is clear, does not self reference and universally
> >> applies to all BSPs. It removes the defaults from LibBSD and lets us manage them
> >> in rtems.git for a BSP. Explicitly requiring a BSP to provide support lets a
> >> user easily check any BSP to see what cache coherent memory is configured and
> >> what the bus handlers are.
> >>
> >>> It shall also define BSP_INITIAL_EXTENSION (normally via #include
> >>> <bsp/default-initial-extension.h>).
> >> This is a recent addition and it is the only piece I found that has an issue
> >> when building the motorola_powerpc. Maybe the way this is implemented is needs
> >> to be reconsidered or we accept bsp.h does include rtems.h either directly or
> >> indirectly.
> >>
> >> The ability to interchange either bsp.h or rtems.h or having code that depends
> >> on one because you include the other seems wrong.
> >
> > We should move away from BSP-specific interfaces.
>
> Could you please expand a little on this? I am wondering how "interfaces" is
> being use here.
>
> Would a bsp/bus.h interface based on the macros I listed in this thread's patch
> work as a start?
>
> I have isolated around 5 powerpc BSPs that would need to be updated as a set...
>
>  beatnik
>  psim
>  motorola_powerpc
>  mvme5500
>  haleakala
>
> I plan to discuss this tomorrow with Jennifer and Kinsey to figure out how to
> resolve this. Your input and feedback has been valuable.
>
> > The <bsp.h> is the only
> > mandatory header file provided by a BSP and may contain all sorts of things.
>
> Yes it is a bit of a sweeper for a lot of things, a little too much.
>
> > From my point of view the BSP should indicate which features it
> > requires/supports and then it should implement a standard interface.
>
> That would be nice. There are defacto standards in some parts where driver
> sharing required it happen but I think there is no uniform set of interfaces.
>
> A key issue is the size of a task that needs to touch all BSPs. We tend to look
> at blocks of work in the generic areas or as a specific BSP or family of BSPs.
> Large refactoring of BSPs is hard to get funding for and hard to test.
>
Doing one BSP could be a GSoC-scope proof-of-concept?

If this gets a little bit more detail/requirements, an open project
ticket could be created.

> > The bus API implementation in FreeBSD is architecture-specific.
>
> It is and I am fine with how we currently have thing implemented in libbsd. The
> x86 needs its own bus API and I reviewed the rtemsbsd shared bus support and it
> currently fits most cases I can see. I wondered about a powerpc specific bus
> version and all I would end up doing is the same thing we have in rtemsbsd plus
> something like the patch in this thread. I also reviewed the FreeBSD
> implementation for the powerpc, we should avoid it.
>
> > We can do this in RTEMS as
> > well and do the implementation in cpukit, for example based on the riscv
> > implementation in FreeBSD. The BSP could then simply indicate if it needs a full
> > featured implementation or the simple inline implementation we have currently.
>
> Yeah this sound nice.
>
> > The definition of BSP_INITIAL_EXTENSION can move to a separate header file.
>
> I wonder about this but I could not see how to implement it.
>
> > The cache coherent memory is a different topic and I think this is already
> > sorted out in
> >
> > http://devel.rtems.org/ticket/4243
>
> Yes and I hopefully have an elegant solution in mind for those BSPs who
> currently depend on the default heap allocation. I included it here to make the
> list of rules as complete as possible to avoid the post appearing in searches
> and being confused as "the" list.
>
> Chris
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