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References: <20220511181935.810735-1-lyude@redhat.com>
In-Reply-To: <20220511181935.810735-1-lyude@redhat.com>
From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Wed, 11 May 2022 14:36:23 -0400
Message-ID: <CADnq5_OWH-Bat3OyCmHz6hTE++7hPLXqqMgg2=Nk6HB_Qk61JA@mail.gmail.com>
Subject: Re: [PATCH] drm/amdgpu: Add 'modeset' module parameter
To:     Lyude Paul <lyude@redhat.com>
Cc:     amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Andrey Grodzovsky <andrey.grodzovsky@amd.com>,
        David Airlie <airlied@linux.ie>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:DRM DRIVERS" <dri-devel@lists.freedesktop.org>,
        Solomon Chiu <solomon.chiu@amd.com>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Alex Deucher <alexander.deucher@amd.com>,
        Evan Quan <evan.quan@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>
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On Wed, May 11, 2022 at 2:20 PM Lyude Paul <lyude@redhat.com> wrote:
>
> Many DRM drivers feature a 'modeset' argument, which can be used to
> enable/disable the entire driver (as opposed to passing nomodeset to the
> kernel, which would disable modesetting globally and make it difficult to
> load amdgpu afterwards). Apparently amdgpu is actually missing this
> however, so let's add it!

You can already do that by passing modprobe.blacklist=amdgpu on the
kernel command line.  I don't think we need another option to do that.


>
> Keep in mind that this currently just lets one enable or disable amdgpu, I
> haven't bothered adding a headless mode like nouveau has - however I'm sure
> someone else can add this if needed.

You can do this as well by passing an IP block mask which disables the
display IP, or media IP, etc.

Alex

>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index ebd37fb19cdb..24e6fb4517cc 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -872,6 +872,15 @@ MODULE_PARM_DESC(smu_pptable_id,
>         "specify pptable id to be used (-1 = auto(default) value, 0 = use pptable from vbios, > 0 = soft pptable id)");
>  module_param_named(smu_pptable_id, amdgpu_smu_pptable_id, int, 0444);
>
> +/**
> + * DOC: modeset (int)
> + * Used to enable/disable modesetting for amdgpu exclusively.
> + */
> +bool amdgpu_enable_modeset = true;
> +MODULE_PARM_DESC(modeset,
> +                "Enable or disable display driver (1 = on (default), 0 = off");
> +module_param_named(modeset, amdgpu_enable_modeset, bool, 0444);
> +
>  /* These devices are not supported by amdgpu.
>   * They are supported by the mach64, r128, radeon drivers
>   */
> @@ -2003,6 +2012,11 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
>         bool is_fw_fb;
>         resource_size_t base, size;
>
> +       if (!amdgpu_enable_modeset) {
> +               DRM_INFO("modeset=0 passed to amdgpu, driver will not be enabled\n");
> +               return -ENODEV;
> +       }
> +
>         /* skip devices which are owned by radeon */
>         for (i = 0; i < ARRAY_SIZE(amdgpu_unsupported_pciidlist); i++) {
>                 if (amdgpu_unsupported_pciidlist[i] == pdev->device)
> --
> 2.35.1
>