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From: Jose Fernandez <josef@netflix.com>
To: Harry Wentland <harry.wentland@amd.com>,
	Leo Li <sunpeng.li@amd.com>,
	Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
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	Ilya Bakoulin <ilya.bakoulin@amd.com>,
	Nasir Osman <nasir.osman@amd.com>,
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	Leo Ma <hanghong.ma@amd.com>,
	amd-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org,
	Jose Fernandez <josef@netflix.com>
Subject: [PATCH] drm/amd/display: Fix division by zero in setup_dsc_config
Date: Tue,  9 Apr 2024 22:34:33 -0600
Message-Id: <20240410043433.12854-1-josef@netflix.com>
Precedence: bulk
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When slice_height is 0, the division by slice_height in the calculation
of the number of slices will cause a division by zero driver crash. This
leaves the kernel in a state that requires a reboot. This patch adds a
check to avoid the division by zero.

The stack trace below is for the 6.8.4 Kernel. I reproduced the issue on
a Z16 Gen 2 Lenovo Thinkpad with a Apple Studio Display monitor
connected via Thunderbolt. The amdgpu driver crashed with this exception
when I rebooted the system with the monitor connected.

kernel: ? die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434 arch/x86/kernel/dumpstack.c:447)
kernel: ? do_trap (arch/x86/kernel/traps.c:113 arch/x86/kernel/traps.c:154)
kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
kernel: ? do_error_trap (./arch/x86/include/asm/traps.h:58 arch/x86/kernel/traps.c:175)
kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
kernel: ? exc_divide_error (arch/x86/kernel/traps.c:194 (discriminator 2))
kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
kernel: ? asm_exc_divide_error (./arch/x86/include/asm/idtentry.h:548)
kernel: ? setup_dsc_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1053) amdgpu
kernel: dc_dsc_compute_config (drivers/gpu/drm/amd/amdgpu/../display/dc/dsc/dc_dsc.c:1109) amdgpu

After applying this patch, the driver no longer crashes when the monitor
is connected and the system is rebooted. I believe this is the same
issue reported for 3113.

Signed-off-by: Jose Fernandez <josef@netflix.com>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3113
---
 drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
index ac41f9c0a283..597d5425d6cb 100644
--- a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
+++ b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
@@ -1055,7 +1055,12 @@ static bool setup_dsc_config(
 	if (!is_dsc_possible)
 		goto done;
 
-	dsc_cfg->num_slices_v = pic_height/slice_height;
+	if (slice_height > 0)
+		dsc_cfg->num_slices_v = pic_height/slice_height;
+	else {
+		is_dsc_possible = false;
+		goto done;
+	}
 
 	if (target_bandwidth_kbps > 0) {
 		is_dsc_possible = decide_dsc_target_bpp_x16(
-- 
2.44.0