Re: [RFC][PATCH] axi: add AXI bus driver

["Rafał Miłecki" <zajec5@gmail.com>]

2011/4/12 Hauke Mehrtens <hauke@hauke-m.de>:
> Hi Rafał,
>
> On 04/12/2011 09:27 PM, Rafał Miłecki wrote:
>> 2011/4/12 George Kashperko <george@znau.edu.ua>:
>>>
>>>> 2011/4/12 George Kashperko <george@znau.edu.ua>:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> On Tue, Apr 12, 2011 at 01:57:07AM +0200, Rafał Miłecki wrote:
>>>>>>> Cc: Michael Büsch <mb@bu3sch.de>
>>>>>>> Cc: Larry Finger <Larry.Finger@lwfinger.net>
>>>>>>> Cc: George Kashperko <george@znau.edu.ua>
>>>>>>> Cc: Arend van Spriel <arend@broadcom.com>
>>>>>>> Cc: linux-arm-kernel@lists.infradead.org
>>>>>>> Cc: Russell King <rmk@arm.linux.org.uk>
>>>>>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>>>>>> Cc: Andy Botting <andy@andybotting.com>
>>>>>>> Cc: linuxdriverproject <devel@linuxdriverproject.org>
>>>>>>> Cc: linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>
>>>>>>> Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
>>>>>>> ---
>>>>>>> V2: Rename to axi
>>>>>>>     Use DEFINE_PCI_DEVICE_TABLE in bridge
>>>>>>>     Make use of pr_fmt and pr_*
>>>>>>>     Store core class
>>>>>>>     Rename bridge to not b43 specific
>>>>>>>     Replace magic 0x1000 with BCMAI_CORE_SIZE
>>>>>>>     Remove some old "ssb" names and defines
>>>>>>>     Move BCMAI_ADDR_BASE def
>>>>>>>     Add drvdata field
>>>>>>> V3: Fix reloading (kfree issue)
>>>>>>>     Add 14e4:0x4331
>>>>>>>     Fix non-initialized struct issue
>>>>>>>     Drop useless inline functions wrappers for pci core drv
>>>>>>>     Proper pr_* usage
>>>>>>> V3.1: Include forgotten changes (pr_* and include related)
>>>>>>>     Explain why we dare to implement empty release function
>>>>>>
>>>>>> I'm not sure we need this. If you have an IP Core which talks AXI and
>>>>>> you want to put it on a PCI bus, you will have a PCI Bus wrapper around
>>>>>> that IP Core, so you should go and let the kernel know about that. See
>>>>>> [1] for a core IP which talks AXI and [2] for a PCI bus glue layer.
>>>>>>
>>>>>> Besides, if you introduce this bus layer, it'll be more difficult for
>>>>>> other licensees of the same core to re-use the same driver, since it's
>>>>>> now talking a PCI emulated on top of AXI. The same can be achieved with
>>>>>> the platform_bus which is more widely used, specially on ARM SoCs.
>>>>>>
>>>>>> [1] http://gitorious.org/usb/usb/blobs/dwc3/drivers/usb/dwc3/core.c
>>>>>> [2] http://gitorious.org/usb/usb/blobs/dwc3/drivers/usb/dwc3/dwc3-haps.c
>>>>>>
>>>>>
>>>>> Already noticed earlier that AXI isnt really good name for
>>>>> Broadcom-specific axi bus customization. As of tech docs available from
>>>>> arm, corelink AXI cores use own identification registers which feature
>>>>> different format and layout comparing to that we use for Broadcom cores.
>>>>>
>>>>> Maybe there is something "standartized" by the DMP specs? If so I'm
>>>>> curious if that DMP is obligatory for every axi bus ?
>>>>>
>>>>> Naming particular Broadcom's implementation just axi limits other
>>>>> licensees in reusing axi bus name/code or will require hacks/workarounds
>>>>> from them to fit Broadcom-like core scanning/identificating techniques.
>>>>> You use bus named AXI to group and manage Broadcom cores, while never
>>>>> even publish device records for native axi cores Broadcom use to talk to
>>>>> the interconnect through. Yet again, something like bcmb/bcmai looks
>>>>> like better name for this bus.
>>>>
>>>> I don't know, I'm really tired of this. Earlier I was told to not use
>>>> anything like bcmai, because it is not Broadcom specific. Now it seems
>>>> (and I'm afraid I agree) there is quite a lot of Broadcom specific
>>>> stuff.
>>> Well, _if_ that "magic" EROM core layout is arm's "standard" for axi
>>> ports identification _and_ _if_ that EROM core is obligatory axi
>>> component then sure axi name is good one as soon as you consider
>>> registering master port (agent) cores with device subsystem as well.
>>> I have no clue here about how resolve those _if_'s, hopefully Broadcom
>>> guys can enlighten us on the subject.
>>
>> Do you think that in my code only scanning is Broadcom specific? In
>> such a case we could keep it "axi", and just s/scan/bcmscan/. This is
>> only correct choice if the rest (addressing, core enabling, host
>> management) is AXI specific.
>
> The specification for the AMBA AXI Interface is available for free
> download from ARM if you register to their website and accept their license:
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.set.amba/index.html
> I got it from there without any problems and the license does not look
> too bad for me, by having a quick look at it. I do not know if it will
> help you in any way or if it is completely unrelated.
>
> Why is the existing support for the amba bus not extended or used in any
> way for this? It exists for some time in drivers/amba/. There already
> was a discussion about this in https://lkml.org/lkml/2011/3/30/186 , but
> with no result as I see.

I can see exactly nothing I could use from whatever driver/amba is.
What does it do from things we need? How do you imagine using that
with out (non)Broadcom buses?

-- 
Rafał