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Subject: Re: [RESEND PATCH 0/6] rapidio: move Kconfig menu definition to
 subsystem
To:     Russell King - ARM Linux <linux@armlinux.org.uk>,
        Alexei Colin <acolin@isi.edu>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        John Paul Walters <jwalters@isi.edu>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Will Deacon <will.deacon@arm.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>,
        Alexander Sverdlin <alexander.sverdlin@nokia.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Anvin <hpa@zytor.com>,
        Matt Porter <mporter@kernel.crashing.org>, x86@kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-mips@linux-mips.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20180731142954.30345-1-acolin@isi.edu>
 <20180731155909.GO17271@n2100.armlinux.org.uk>
From:   Alex Bounine <alex.bou9@gmail.com>
Message-ID: <1f427e4c-3fb8-769a-efb6-db64afd4617a@gmail.com>
Date:   Tue, 31 Jul 2018 14:21:57 -0400
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On 2018-07-31 11:59 AM, Russell King - ARM Linux wrote:
> For the thread associated with this patch set, a review of a previous
> patch for ARM posted last Tuesday on this subject asked a series of
> questions about the PCI-nature of this.  The review has not been
> responded to.

We are dealing with this now. More appropriate to do it this time than 
before having reworked set.

> If it is inappropriate to offer RapidIO for any architecture that
> happens to has PCI, then it is inappropriate to offer it for any
> ARM machine that happens to have PCI.

It is completely appropriate to use RapidIO on any architecture that has 
PCI/PCIe using existing PCIe-to-SRIO host bridges. Works well with 
Marvell and NVIDIA boards.

Confusion here is caused by the fact that there are ARM and non-ARM 
devices that offer on-chip RapidIO host controllers as well as PCIe. 
E.g. TI Keystone/KeystoneII, FSL 85xx/86xx, Xilinx and Altera FPGAs with 
ARM cores, Cavium on MIPS. In most cases external buses are configurable 
and we have to address possible combinations.

I already posted some explanation in response to your earlier comment.

> In light of the lack of explanation on this point so far, I'm naking
> the ARM part of this series for now.
> 

Explanations posted.

> I also think that the HAS_RAPIDIO thing is misleading and needs
> sorting out (as I've mentioned in other emails, including the one
> I refer to above) before rapidio becomes available more widely.
>
Highly likely it is used right now in a base station of mobile operator 
near you :)

> On Tue, Jul 31, 2018 at 10:29:48AM -0400, Alexei Colin wrote:
>> Resending the patchset from prior submission:
>> https://lkml.org/lkml/2018/7/30/911
>>
>> The only change are the Cc tags in all patches now include the mailing
>> lists for all affected architectures, and patch 1/6 (which adds the menu
>> item to RapdidIO subsystem Kconfig) is CCed to all maintainers who are
>> getting this cover letter. The cover letter has been updated with
>> explanations to points raised in the feedback.
>>
>>
>>
>> The top-level Kconfig entry for RapidIO subsystem is currently
>> duplicated in several architecture-specific Kconfig files. This set of
>> patches does two things:
>>
>> 1. Move the Kconfig menu definition into the RapidIO subsystem and
>> remove the duplicate definitions from arch Kconfig files.
>>
>> 2. Enable RapidIO Kconfig menu entry for arm and arm64 architectures,
>> where it was not enabled before. I tested that subsystem and drivers
>> build successfully for both architectures, and tested that the modules
>> load on a custom arm64 Qemu model.
>>
>> For all architectures, RapidIO menu should be offered when either:
>> (1) The platform has a PCI bus (which host a RapidIO module on the bus).
>> (2) The platform has a RapidIO IP block (connected to a system bus, e.g.
>> AXI on ARM). In this case, 'select HAS_RAPIDIO' should be added to the
>> 'config ARCH_*' menu entry for the SoCs that offer the IP block.
>>
>> Prior to this patchset, different architectures used different criteria:
>> * powerpc: (1) and (2)
>> * mips: (1) and (2) after recent commit into next that added (2):
>>    https://www.linux-mips.org/archives/linux-mips/2018-07/msg00596.html
>>    fc5d988878942e9b42a4de5204bdd452f3f1ce47
>>    491ec1553e0075f345fbe476a93775eabcbc40b6
>> * x86: (1)
>> * arm,arm64: none (RapidIO menus never offered)
>>
>> This set of architectures are the ones that implement support for
>> RapidIO as system bus. On some platforms RapidIO can be the only system
>> bus available replacing PCI/PCIe.  As it is done now, RapidIO is
>> configured in "Bus Options" (x86/PPC) or "Bus Support" (ARMs) sub-menu
>> and from system configuration option it should be kept this way.
>> Current location of RAPIDIO configuration option is familiar to users of
>> PowerPC and x86 platforms, and is similarly available in some ARM
>> manufacturers kernel code trees. (Alex Bounine)
>>
>> HAS_RAPIDIO is not enabled unconditionally, because HAS_RAPIDIO option
>> is intended for SOCs that have built in SRIO controllers, like TI
>> KeyStoneII or FPGAs. Because RapidIO subsystem core is required during
>> RapidIO port driver initialization, having separate option allows us to
>> control available build options for RapidIO core and port driver (bool
>> vs.  tristate) and disable module option if port driver is configured as
>> built-in. (Alex Bounine)
>>
>> Responses to feedback from prior submission (thanks for the reviews!):
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2018-July/593347.html
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2018-July/593349.html
>>
>> Changelog:
>>    * Moved Kconfig entry into RapidIO subsystem instead of duplicating
>>
>> In the current patchset, I took the approach of adding '|| PCI' to the
>> depends in the subsystem. I did try the alterantive approach mentioned
>> in the reviews for v1 of this patch, where the subsystem Kconfig does
>> not add a '|| PCI' and each per-architecture Kconfig has to add a
>> 'select HAS_RAPIDIO if PCI' and SoCs with IP blocks have to also add
>> 'select HAS_RAPIDIO'. This works too but requires each architecture's
>> Kconfig to add the line for RapidIO (whereas current approach does not
>> require that involvement) and also may create a false impression that
>> the dependency on PCI is strict.
>>
>> We appreciate the suggestion for also selecting the RapdiIO subsystem for
>> compilation with COMPILE_TEST, but hope to address it in a separate
>> patchset, localized to the subsystem, since it will need to change
>> depends on all drivers, not just on the top level, and since this
>> patch now spans multiple architectures.
>>
>> Alexei Colin (6):
>>    rapidio: define top Kconfig menu in driver subtree
>>    x86: factor out RapidIO Kconfig menu
>>    powerpc: factor out RapidIO Kconfig menu entry
>>    mips: factor out RapidIO Kconfig entry
>>    arm: enable RapidIO menu in Kconfig
>>    arm64: enable RapidIO menu in Kconfig
>>
>>   arch/arm/Kconfig        |  2 ++
>>   arch/arm64/Kconfig      |  2 ++
>>   arch/mips/Kconfig       | 11 -----------
>>   arch/powerpc/Kconfig    | 13 +------------
>>   arch/x86/Kconfig        |  8 --------
>>   drivers/rapidio/Kconfig | 15 +++++++++++++++
>>   6 files changed, 20 insertions(+), 31 deletions(-)
>>
>> -- 
>> 2.18.0
>>
>