linux-kernel - Re: [PATCH] drm/radeon: avoid bogus "vram limit (0) must be a power of 2" warning

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Date:   Wed, 6 Jul 2022 17:52:18 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Mateusz Jończyk <mat.jonczyk@...pl>
Cc:     amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Gray <jsg@....id.au>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH] drm/radeon: avoid bogus "vram limit (0) must be a power
 of 2" warning

Applied.  Thanks!

Alex

On Wed, Jul 6, 2022 at 5:40 PM Mateusz Jończyk <mat.jonczyk@...pl> wrote:
>
> I was getting the following message on boot on Linux 5.19-rc5:
>         radeon 0000:01:05.0: vram limit (0) must be a power of 2
> (I didn't use any radeon.vramlimit commandline parameter).
>
> This is caused by
> commit 8c2d34eb53b9 ("drm/radeon: use kernel is_power_of_2 rather than local version")
> which removed radeon_check_pot_argument() and converted its users to
> is_power_of_2(). The two functions differ in its handling of 0, which is
> the default value of radeon_vram_limit: radeon_check_pot_argument()
> "incorrectly" considered it a power of 2, while is_power_of_2() does not.
>
> An appropriate conditional silences the warning message.
>
> It is not necessary to add a similar test to other callers of
> is_power_of_2() in radeon_device.c. The matching commit in amdgpu:
> commit 761175078466 ("drm/amdgpu: use kernel is_power_of_2 rather than local version")
> is unaffected by this bug.
>
> Tested on Radeon HD 3200.
>
> Not ccing stable, this is not serious enough.
>
> Fixes: 8c2d34eb53b9 ("drm/radeon: use kernel is_power_of_2 rather than local version")
> Cc: Alex Deucher <alexander.deucher@....com>
> Cc: Christian König <christian.koenig@....com>
> Cc: "Pan, Xinhui" <Xinhui.Pan@....com>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: Jonathan Gray <jsg@....id.au>
> Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
> ---
>  drivers/gpu/drm/radeon/radeon_device.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
> index 15692cb241fc..429644d5ddc6 100644
> --- a/drivers/gpu/drm/radeon/radeon_device.c
> +++ b/drivers/gpu/drm/radeon/radeon_device.c
> @@ -1113,7 +1113,7 @@ static int radeon_gart_size_auto(enum radeon_family family)
>  static void radeon_check_arguments(struct radeon_device *rdev)
>  {
>         /* vramlimit must be a power of two */
> -       if (!is_power_of_2(radeon_vram_limit)) {
> +       if (radeon_vram_limit != 0 && !is_power_of_2(radeon_vram_limit)) {
>                 dev_warn(rdev->dev, "vram limit (%d) must be a power of 2\n",
>                                 radeon_vram_limit);
>                 radeon_vram_limit = 0;
>
> base-commit: 88084a3df1672e131ddc1b4e39eeacfd39864acf
> --
> 2.25.1
>