linux-kernel - Re: [PATCH] nouveau: make backlight support non optional

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Message-ID: <CACO55tswMuDE9u3asU2Ls7BhA0uKGGarLk+E-WTD6MVnLwc3tw@mail.gmail.com>
Date:   Sat, 24 Jul 2021 16:13:27 +0200
From:   Karol Herbst <kherbst@...hat.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lyude Paul <lyude@...hat.com>, Ben Skeggs <bskeggs@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Daniel Vetter <daniel@...ll.ch>,
        ML nouveau <nouveau@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] nouveau: make backlight support non optional

On Sat, Jul 24, 2021 at 4:05 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Sat, Jul 24, 2021 at 2:52 PM Karol Herbst <kherbst@...hat.com> wrote:
> >
> > On Sat, Jul 24, 2021 at 2:10 PM Karol Herbst <kherbst@...hat.com> wrote:
> > >
> > > On Sat, Jul 24, 2021 at 1:56 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > > >
> > > > On Sat, Jul 24, 2021 at 11:55 AM Karol Herbst <kherbst@...hat.com> wrote:
> > > >
> > > > - You run into dependency loops that prevent a successful build when some
> > > >    other driver has a 'depends on'. Preventing these loops was the main
> > > >    reason I said we should do this change.
> > > >
> > > > In theory we could change the other 85 drivers that use 'depends on' today,
> > > > and make BACKLIGHT_CLASS_DEVICE a hidden symbol that only ever
> > > > selected by the drivers that need it. This would avoid the third problem but
> > > > not the other one.
> > > >
> > > I see. Yeah, I guess we can do it this way then. I just wasn't aware
> > > of the bigger picture here. Thanks for explaining.
> >
> > yeah... that doesn't work. So the issue is, that X86_PLATFORM_DEVICES
> > is a little bit in the way. If I remove the select
> > X86_PLATFORM_DEVICES then I guess problems once ACPI is enabled, but
> > if I keep it, I get cyclic dep errors :/
>
> Right, this is the exact problem I explained: since all other drivers use
> 'depends on X86_PLATFORM_DEVICES' instead of 'select', you get a
> loop again. Prior to changing the BACKLIGHT_CLASS_DEVICE dependency,
> nouveau was pretty much on top of everything else in the hierarchy,
> changing part of it can result in a loop.
>
> I see that there are about ten more 'select' statements that look like
> they should not be there, and almost all of them were added in order
> to be able to 'select MXM_WMI'.
>
> I think we can go as far as the patch below, which I've put in my
> randconfig build machine, on top of your patch. I'm not entirely
> sure how strong the dependency on MXM_WMI is: does it cause
> a build failure when that is not enabled, or was this select just
> added for convenience so users don't get surprised when it's missing?
>
>        Arnd
>

we use the MXM_WMI in code. We also have to keep arm in mind and not
break stuff there. So I will try to play around with your changes and
see how that goes.

> diff --git a/drivers/gpu/drm/nouveau/Kconfig b/drivers/gpu/drm/nouveau/Kconfig
> index 9c2108b48524..f2585416507e 100644
> --- a/drivers/gpu/drm/nouveau/Kconfig
> +++ b/drivers/gpu/drm/nouveau/Kconfig
> @@ -3,21 +3,14 @@ config DRM_NOUVEAU
>         tristate "Nouveau (NVIDIA) cards"
>         depends on DRM && PCI && MMU
>         depends on AGP || !AGP
> +       depends on ACPI_VIDEO || !ACPI
> +       depends on BACKLIGHT_CLASS_DEVICE
> +       depends on MXM_WMI || !X86 || !ACPI
>         select IOMMU_API
>         select FW_LOADER
>         select DRM_KMS_HELPER
>         select DRM_TTM
>         select DRM_TTM_HELPER
> -       select BACKLIGHT_CLASS_DEVICE
> -       select ACPI_VIDEO if ACPI && X86 && INPUT
> -       select X86_PLATFORM_DEVICES if ACPI && X86
> -       select ACPI_WMI if ACPI && X86
> -       select MXM_WMI if ACPI && X86
> -       select POWER_SUPPLY
> -       # Similar to i915, we need to select ACPI_VIDEO and it's dependencies
> -       select INPUT if ACPI && X86
> -       select THERMAL if ACPI && X86
> -       select ACPI_VIDEO if ACPI && X86
>         select SND_HDA_COMPONENT if SND_HDA_CORE
>         help
>           Choose this option for open-source NVIDIA support.
>