linux-kernel - Re: [PATCH] dmaengine: ARM_DMA350 should depend on ARM/ARM64

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Message-ID: <CAMuHMdWoxPc71YYrEMdPwdq-HOhmP2jNiwo1+-8o6_v4YJ0NHQ@mail.gmail.com>
Date: Wed, 23 Apr 2025 16:34:26 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Robin Murphy <robin.murphy@....com>
Cc: Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: ARM_DMA350 should depend on ARM/ARM64

Hi Robin,

On Wed, 23 Apr 2025 at 15:29, Robin Murphy <robin.murphy@....com> wrote:
> On 2025-04-23 1:17 pm, Vinod Koul wrote:
> > On 23-04-25, 14:13, Geert Uytterhoeven wrote:
> >> On Wed, 23 Apr 2025 at 13:48, Vinod Koul <vkoul@...nel.org> wrote:
> >>> On 23-04-25, 13:11, Geert Uytterhoeven wrote:
> >>>> On Wed, 23 Apr 2025 at 12:59, Robin Murphy <robin.murphy@....com> wrote:
> >>>>> On 2025-04-22 7:11 pm, Geert Uytterhoeven wrote:
> >>>>>> The Arm DMA-350 controller is only present on Arm-based SoCs.
> >>>>>
> >>>>> Do you know that for sure? I certainly don't. This is a licensable,
> >>>>> self-contained DMA controller IP with no relationship whatsoever to any
> >>>>> particular CPU ISA - our other system IP products have turned up in the
> >>>>> wild paired with non-Arm CPUs, so I don't see any reason that DMA-350
> >>>>> wouldn't either.
> >>>>
> >>>> The dependency can always be relaxed later, when the need arises.
> >>>> Note that currently there are no users at all...
>
> Huh? There is now an upstream DT binding, and DTs using that binding
> most certainly already exist - not least the one I have, but I'm not the
> only one. We don't have a requirement that bindings must have
> upstream-supported consumers.

Dependencies in Kconfig are not related to DT bindings, they only
control what can be built?

> >>> True, but do we have any warnings generated as a result, if there are no
> >>> dependency should we still limit a driver to an arch?
> >>
> >> I am not aware of any warnings (I built it on MIPS yesterday ;-).
> >> It is just one more question that pops up during "make oldconfig",
> >> and Linus may notice and complain, too...
>
> Well, yeah? It's a new driver for some (relatively) new hardware; every
> release always adds loads of new drivers for things I don't personally
> care about, so I press "n" a lot when updating my config, just like I
> imagine most other people do, Linus included.

Please read [1] and ask yourself if Linux wants to see a question
about Arm DMA-350 when configuring a kernel for his AMD Threadripper
workstation...

> > True, give there are no users, lets pick this and drop if we get a non
> > arm user
>
> Well by that logic surely it should just depend on COMPILE_TEST, because
> there are no ARM or ARM64 "users" either?

If you want to push it that far, fine for me ;-)

> FWIW the not-quite-upstream platform I developed on (a custom build of
> fvp-base-revc with a DMA-350 component added) did happen to be ARM64, as
> are some other Arm-internal designs and one available SoC that I do know
> of containing DMA-350; I am not aware of any Linux-capable 32-bit
> platforms to justify an ARM dependency, so I'd consider that just as
> arbitrarily pulled out of thin air.

OK, then the ARM dependency can be dropped for now.
I had done a quick Google search to find SoCs that contain a DMA-350
instance, and had only found a Cortex-M0-based SoC, so I assumed it
would be used on ARM, too.

> But then to pick another example at random, XILINX_DMA equally has no
> "users", so please make that depend on something arbitrary as well for
> consistency; it's only fair.

Sure, there are lots of Kconfig symbols that could benefit from
additional dependencies. Unfortunately my time is limited, so usually
I create and send patches for new Kconfig symbols only....

Thanks!

[1] https://lore.kernel.org/all/CAHk-=wg+38EHPKGou1MqXwAAXC30cM8sMgZAGnZ7TcFO4L9J2w@mail.gmail.com

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