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

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Message-Id: <20220706200144.68851-1-mat.jonczyk@o2.pl>
Date:   Wed,  6 Jul 2022 22:01:44 +0200
From:   Mateusz Jończyk <mat.jonczyk@...pl>
To:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     Mateusz Jończyk <mat.jonczyk@...pl>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Jonathan Gray <jsg@....id.au>
Subject: [PATCH] drm/radeon: avoid bogus "vram limit (0) must be a power of 2" warning

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