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

George Kashperko
2011-04-12T20:39:45Z

> 2011/4/12 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?
>
> 1) I checked for amba_device_register:
> http://lxr.free-electrons.com/ident?i=amba_device_register
> and do not understand that. There are a lot of drivers registering
> some pre-defined devices. I could not find any driver scanning for
> amba devices and registering them. Are we going to be the first driver
> registering devices dynamically or do I get this totally wrong
>
> 2) amba_id contains only some interesting "id". How can we relate this
> with our core id/rev/manuf/class?
I guess that id corresponds to corelink-compatible peripheral/component
4x8bit registers' layout.

> 3) There is no code for managing AMBA cores (enable, checking status,
> disabling, resetting)...
These could be of interest for DMP core driver if someone decide to
publish agent cores on amba_bustype.

>
> That way I see really low (or not at all) relation between out
> (not)Broadcom bus and present AMBA bus.
>
Agree.

Have nice day,