Re: [PATCH 6/6] arm64: enable RapidIO menu in Kconfig

From: Alex Bounine
Date: Wed Aug 01 2018 - 11:14:16 EST

On 2018-08-01 06:38 AM, Russell King - ARM Linux wrote:
On Tue, Jul 31, 2018 at 04:01:27PM -0400, Alex Bounine wrote:
On 2018-07-31 02:18 PM, Russell King - ARM Linux wrote:
On Tue, Jul 31, 2018 at 01:59:27PM -0400, Alex Bounine wrote:
On 2018-07-31 11:52 AM, Russell King - ARM Linux wrote:
On Tue, Jul 31, 2018 at 08:54:14AM -0400, Alex Bounine wrote:
On 2018-07-31 04:41 AM, Will Deacon wrote:
On Mon, Jul 30, 2018 at 06:50:34PM -0400, Alexei Colin wrote:
Platforms with a PCI bus will be offered the RapidIO menu since they may
be want support for a RapidIO PCI device. Platforms without a PCI bus
that might include a RapidIO IP block will need to "select HAS_RAPIDIO"
in the platform-/machine-specific "config ARCH_*" Kconfig entry.

Tested that kernel builds for arm64 with RapidIO subsystem and
switch drivers enabled, also that the modules load successfully
on a custom Aarch64 Qemu model.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: John Paul Walters <jwalters@xxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx,
Signed-off-by: Alexei Colin <acolin@xxxxxxx>
arch/arm64/Kconfig | 2 ++
1 file changed, 2 insertions(+)

Thanks, this looks much cleaner than before:

Acked-by: Will Deacon <will.deacon@xxxxxxx>

The only thing I'm not sure about is why we don't just select HAS_RAPIDIO
unconditionally in the arm64 Kconfig. Does selecting only that option
actually pull in new code to the build?

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

Your explanation doesn't make much sense to me.

RAPIDIO is the bus-level support, right? So drivers that depend on
the bus-level support should depend on RAPIDIO, and so, if RAPIDIO
is configured as a module, they will also be allowed to be disabled
or a module, but not built-in if tristate. If it is boolean, and
causes the driver to be built-in to the kernel, then you need to use
"RAPIDIO=y" so that it's dependency is only satisfied when the core
is built-in.

RapidIO host controllers (on local bus like SoC internal or PCIe) are
serviced by MPORT device drivers that are subsystem specific and communicate
with RapidIO core using set of callbacks. Depending on HW architecture these
drivers may be defined as built-in or module.

Why does hardware architecture define whether something has to be built
in or can be modular?

It is the case today that (eg) on-SoC hardware _can_ be built as a module
if desired - just because it's on the SoC does not mean it has to be
built in to the kernel. Why is RapidIO any different?

Not HW architecture - legacy can be blamed as well. Freescale's FSL_RIO
driver still exist as built-in so far. Intent of this patch set is to allow
RapidIO support in more architectures without reworking old stuff.
I do not think that anyone will be updating FSL_RIO driver soon.

Sorry, but I'm even more confused. If it's not hardware architecture,
then why did you say previously "Depending on HW architecture these
drivers may be defined as built-in or module." ?

My fault, I took some shortcuts in writing here and that made it not clear enough. In this case I was talking about legacy code existing in PowerPC architecture branch. FSL_RIO host driver can be built only as built-in what forces RIO core to be built-in as well.

If it's that the driver isn't written to be a module, then that is not
"HW architecture". Are you just trying to muddy the water?

Not at all :) See above. Driver within architectural branch.

Also we cannot dictate to developers of future drivers which method to use -
they may have built-in option only for the first release.

How is that any different from all the other drivers that we have?

If a driver can only be built-in, then we do this in the Kconfig:

bool "Support driverfoo"
depends on SUBSYSTEM=y

which ensures that the driver can only be built when it's dependent
subsystem is also built-in.

There is another alternative way, which is:


bool "Support driverfoo"

tristate "Support driverbar"

and "SUBSYSTEM" will automatically adopt either 'm' or 'y' correctly
depending on whether any drivers are built-in or not.


Unfortunately we have on hands dependency between mport driver build mode
and RapidIO core which we need to respect.

How is that any different from (eg) hundreds of network drivers and the
networking core code that we already have? That doesn't have such a
convoluted configuration system, and what you have is much simpler.

For example, can you point out why my idea I present below would not

See below.

For peripheral devices attached to the RapidIO fabric such dependency on
local mport implementation does not exist and therefore they all can be
treated as tristate.

HAS_RAPIDIO gives the impression that it defines whether or not
the rapidio core code is allowable or not - it doesn't suggest that
it has anything to do with drivers. However, reading the PowerPC
Kconfig files, it seems to be used that way. That's confusing, and
ought to be fixed. From what I can tell, it's only used for FSL_RIO,
so I suggest that gets converted to:

bool PCI

PCI and RAPIDIO can be mutually exclusive.

Please explain this in light of your patches which contain:

Availability of PCIe and RapidIO can be mutually exclusive on specific boards.
On oter boards we may have both buses at the same time.
Any platform with PCIe can add RapidIO support using PCIe-to-SRIO host bridge.

config RAPIDIO
tristate "RapidIO support"
depends on HAS_RAPIDIO || PCI

This allows RAPIDIO can be selected when PCI is enabled. Therefore,
PCI and RAPIDIO *are not* mutually exclusive as your comment above
states, therefore, I have to assume that your comment is wrong.

config RAPIDIO
tristate "RapidIO support"
depends on HAS_RAPIDIO

config HAS_FSL_RIO

Introducing new variable HAS_FSL_RIO here. Do you suggest having one for
each ARM-based board that has on-chip RIO?

No, I'm suggesting a solution for what I see in the kernel tree today,
which is frankly a mess for the reasons I've already outlined.

HAS_FSL_RIO is based on the _only_ SoC driver apparently in the tree
based on what I could find in the arch/*/Kconfig files. If you don't
think having individual HAS_* options in this way is appropriate,
then maybe instead having per-SoC hidden HAS_* config options are
more appropriate.

This is what we are trying to use here: per-SoC option HAS_RAPIDIO. While the name does not have an individual designation (like HAS_FSL_RIO) it will be only the SoC in the given system that selects it. This will enable RapidIO configuration menu, allowing user to go ahead with remaining RIO configuration. Enabling on-chip port stays as per-SoC option.

Having PCIe bus brings another twist because PCIe-to-SRIO bridge can be used when HAS_RAPIDIO=n. As result every platform that has PCIe should enable RapidIO (except in architectures that do not support RIO at this moment).

config FSL_RIO
bool "Freescale Embedded SRIO Controller support"
depends on RAPIDIO = y && HAS_FSL_RIO

This frees up HAS_RAPIDIO to operate as one would expect - to define
whether or not RAPIDIO should be offered. This also allows:

config ARM

Some SOCs can be configured without PCI. We have confusing action here - we
have to enable PCI on platform that does not have it.

Again, you said above "PCI and RAPIDIO can be mutually exclusive." This
comment self-conflicts with your previous comment.

I explained "mutually exclusive" above.

What you now seem to be saying goes against the patches and the current
Kconfig. You seem to be saying that RAPIDIO _requires_ PCI.

So, we now have three completely different statements from you:
- "we have to enable PCI on platform that does not have it."
- "PCI and RAPIDIO can be mutually exclusive."
- RAPIDIO does not require PCI (since HAS_RAPIDIO=y RAPIDIO=y PCI=n is
a permissible configuration as things stand with PowerPC.)

Which is it?

It seems to be that your replies are just muddying the water - I can
only assume that this is to make us give up. Please don't do that,
it's not in your interest.

Why we cannot use "select HAS_RAPIDIO" HW-specific Kconfig file
(mach-*/Kconfig)? And have on-chip port selection in the same board-specific

As I've already explained, HAS_RAPIDIO has the expectation that it
controls the availability of the RAPIDIO option, not of drivers.
It is HAS_*RAPIDIO*, the clue is in the name. Using it as you are
(basically, to mean that on-SoC rapidio hardware is present) and
allowing such configurations as HAS_RAPIDIO=n RAPIDIO=y PCI=y is
completely counter-intuitive.