Re: Could I (ab)use bus (struct bus_type) for virtual Broadcom bus?

From: Hauke Mehrtens
Date: Thu Apr 14 2011 - 08:34:28 EST

On 04/14/2011 02:04 PM, RafaÅ MiÅecki wrote:
> W dniu 14 kwietnia 2011 13:43 uÅytkownik George Kashperko
> <george@xxxxxxxxxxx> napisaÅ:
>>> We have slightly improved our knowledge of new Broadcom's bus. It
>>> appears Broadcom took standard AMBA bus and put on it two cores for
>>> every device:
>>> 1) First core from each pair is real AMBA device, it has CID and PID.
>>> Broadcom called it wrapper, it is used to control second core
>>> (enabling second, disabling second, resetting second, setting flags of
>>> second).
>>> 2) Second core from each pair is Broadcom specific device. It can
>>> *not* be treated as standard AMBA core - attempting to read it's CID
>>> on PID leads to machine hang. Instead it is identified by MANUF, ID,
>>> REV and CLASS. Example can be 80211 core.
>>> One of the idea is to integrate with current AMBA driver:
>>> 1) First driver read info about all cores in Broadcom specific way. It
>>> registers all *wrapper* (AMBA type) cores as amba_device(s).
>>> 2) Second driver registers for cores with PID 0x103BB369 (Broadcom
>>> specific I believe). It receives wrappers (from AMBA bus) and exposes
>>> wrapper-related Broadcom specific core in the system.
>>> Problem: how to expose Broadcom specific cores in the system? Remember
>>> we can not use amba_device, because Broadcom specific cores are
>>> programmed and identified differently.
>>> Could we register some virtual bcm_amba bus in the system and register
>>> Broadcom specific cores with it? Or is there something better for this
>>> case? In summary everything I need is to make driver (for example b43)
>>> able to register for Broadcom specific core with Broadcom specific
>>> identifiers. For example:
>>> static const struct axi_device_id b43_axi_tbl[] = {
>>> };
>>> MODULE_DEVICE_TABLE(axi, b43_axi_tbl);
>>> We have problems deciding architecture, the whole proposed layout is
>>> not approved as final yet. Right now I try to check possibilities.
>> If you beleive you do need to register broadcom ip core devices on amba
>> bus then I would suggest you to introduce class driver for broadcom
>> cores rather than breaking into bus_type layout. But to be honest I
>> think it is bad idea and your original approach where you managed agents
>> internally and registered _broadcom_ devices on dedicated _broadcom_ bus
>> have much more sense. Going your original way you still can also
>> register agents on amba thus registering two buses per host but honestly
>> registering them just for the sake of registering makes no sense at all.
> I think you may be right, but we got so messed with so many ideas we
> need to clean this out. Our old ideas:
> 1) Extending ssb
> 2) Separated library (brcmaxi)
> 3) Broadcom specific bus (bcmai)
> 4) AMBA AXI bus (axi)
> 5) Integrating with drivers/amba
> I simply decide to consider every idea seriously and decide which will
> fit our needs the best way.
> Hauke: you were proposing integrating with drivers/amba. I really
> expect you to comment on this, please tell us how do you see this now,
> when we have better overview. I took your proposal seriously, you can
> see the results above.

I had no closer look at drivers/amba and this bus driver, I just saw
that there was a discussion about drivers/amba and this implementation
with no result. When the Bradcom cores are not directly connected to
AMBA, but are using some sort of wrapper and there are no benefits in
using drivers/amba, just leave it.

As the implementation of the Braodcom AIX Bus contains some Broadcom
extensions and there seams to be no normal AMBA device being connected
to some Broadcom devices with this special interface number 3) "Broadcom
specific bus (bcmai)" seams to the the best approach in my opinion.

> I think I agree with George that in proposed architecture we are using
> drivers/amba just for the idea of using it. We don't get anything from
> it, we don't provide anything to it that could be used anywhere else.
> I think we should simply take the last version of my patch, rename it
> to bcmamba, fix last issues and commit. It looks we use almos nothing
> AMBA specific in your driver.

This sounds good.

> But as I said, I treat every proposal seriously. So please share your
> minds Hauke & others.

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