linux-kernel - Re: [PATCH] mailbox: ARM_MHU

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Message-ID: <CAMuHMdW8d6_=5Xe8QtmqTzD1dbeE8g8MU183X8uXYp-_hnwDPg@mail.gmail.com>
Date: Tue, 4 Jun 2024 11:57:44 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Cristian Marussi <cristian.marussi@....com>
Cc: Sudeep Holla <sudeep.holla@....com>, Jassi Brar <jassisinghbrar@...il.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mailbox: ARM_MHU_V3 should depend on ARM64

Hi Cristian,

On Tue, Jun 4, 2024 at 11:46 AM Cristian Marussi
<cristian.marussi@....com> wrote:
> On Tue, Jun 04, 2024 at 08:07:18AM +0100, Sudeep Holla wrote:
> > On Mon, Jun 03, 2024 at 07:52:56PM +0200, Geert Uytterhoeven wrote:
> > > On Mon, Jun 3, 2024 at 3:39 PM Sudeep Holla <sudeep.holla@....com> wrote:
> > > > On Wed, May 29, 2024 at 01:36:42PM +0200, Geert Uytterhoeven wrote:
> > > > > On Wed, May 29, 2024 at 12:13 PM Cristian Marussi
> > > > > <cristian.marussi@....com> wrote:
> > > > > > On Wed, May 29, 2024 at 09:30:45AM +0200, Geert Uytterhoeven wrote:
> > > > > > > The ARM MHUv3 controller is only present on ARM64 SoCs.  Hence add a
> > > > > > > dependency on ARM64, to prevent asking the user about this driver when
> > > > > > > configuring a kernel for a different architecture than ARM64.
> > > > > >
> > > > > > the ARM64 dependency was dropped on purpose after a few iterations of
> > > > > > this series since, despite this being an ARM IP, it has really no technical
> > > > > > dependency on ARM arch, not even the usual one on ARM AMBA bus, being this a
> > > > > > platform driver, so it seemed an uneeded artificial restriction to impose...
> > > > > > ...having said that, surely my live testing were performed only on arm64 models
> > > > > > as of now.
> > > > >
> > > > > For that, we have COMPILE_TEST=y.
> > > > >
> > > > > > So, I am not saying that I am against this proposed fix but what is the
> > > > > > issue that is trying to solve, have you seen any compilation error ? or
> > > > > > is it just to avoid the user-prompting ?
> > > > >
> > > > > I did not see a compile error (I didn't enable it on any non-ARM
> > > > > platform).
> > > > >
> > > > > But it is rather futile to ask the user about (thousands of) drivers
> > > > > for hardware that cannot possibly be present on the system he is
> > > > > configuring a kernel for.
> > > >
> > > > I am fine with this fix but I have seen quite opposite argument. That is
> > > > not to add dependency if it is not strictly required.
> > >
> > > Can you please point me to that reference?
> >
> > I don't have one handy, I need to dig but I have been asked to remove
> > in the past.

I guess Linus Torvalds has missed the "ARM MHUv3 Mailbox" question
when configuring his kernel.... Or he has disabled CONFIG_MAILBOX
(it is not enabled in any but a few arm defconfigs).
Oh wait, he runs ARM64 now, so the question was valid ;-)

> > > > Also since you state that the fix is to avoid users of other archs being
> > > > posed with the question that they may get annoyed or can't answer, I
> > > > wonder if the right approach is to make this driver default "n" instead.
> > >
> > > The driver already defaults to "n" (which is the default default ;-)
> >
> > Ah Cristian mentioned the same in private. I may have misunderstood
> > then, for some reason I thought explicit default "n" would avoid getting
> > the prompt.
>
> I just tried this trick, it does not seem to work: an explict default-n will
> anyway trigger a prompt.

The default value does not control the visibility.
Visibility can only be controlled through "{bool,tristate} ... if <condition>",
or through "depends on <condition>".

> > As I said I am fine with the proposed change, just took this discussion
> > as a way to learn little more about Kconfig.
>
> Can this be at least
>
>         depends on ARM || ARM64 || COMPILE_TEST

Only if the MHUv3 can also be present on ARM ("aarch32") SoCs.
Or do people really run 32-bit kernels on ARM64?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds