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

Chris Johns chrisj at rtems.org
Thu Mar 4 18:59:55 UTC 2021

On 5/3/21 2:41 am, Gedare Bloom wrote:
> 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?

I have the MVME 2700 (powerpc/mvme2307) done so that is done. Jennifer and I
will need to sort out the ones on the list so those boards are operational.

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

This is a great idea. I will create a ticket.


>>> 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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