This is a note to let you know that I've just added the patch titled
drm/amdgpu: Avoid overflows/divide-by-zero in latency_watermark calculations.
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-amdgpu-avoid-overflows-divide-by-zero-in-latency_watermark-calculations.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e190ed1ea7458e446230de4113cc5d53b8dc4ec8 Mon Sep 17 00:00:00 2001
From: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
Date: Wed, 29 Mar 2017 22:09:12 +0200
Subject: drm/amdgpu: Avoid overflows/divide-by-zero in latency_watermark calculations.
From: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
commit e190ed1ea7458e446230de4113cc5d53b8dc4ec8 upstream.
At dot clocks > approx. 250 Mhz, some of these calcs will overflow and
cause miscalculation of latency watermarks, and for some overflows also
divide-by-zero driver crash ("divide error: 0000 [#1] PREEMPT SMP" in
"dce_v10_0_latency_watermark+0x12d/0x190").
This zero-divide happened, e.g., on AMD Tonga Pro under DCE-10,
on a Displayport panel when trying to set a video mode of 2560x1440
at 165 Hz vrefresh with a dot clock of 635.540 Mhz.
Refine calculations to avoid the overflows.
Tested for DCE-10 with R9 380 Tonga + ASUS ROG PG279 panel.
Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/dce_v10_0.c | 19 +++----------------
drivers/gpu/drm/amd/amdgpu/dce_v11_0.c | 19 +++----------------
drivers/gpu/drm/amd/amdgpu/dce_v8_0.c | 19 +++----------------
3 files changed, 9 insertions(+), 48 deletions(-)
--- a/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c
@@ -1126,23 +1126,10 @@ static u32 dce_v10_0_latency_watermark(s
a.full = dfixed_const(available_bandwidth);
b.full = dfixed_const(wm->num_heads);
a.full = dfixed_div(a, b);
+ tmp = div_u64((u64) dmif_size * (u64) wm->disp_clk, mc_latency + 512);
+ tmp = min(dfixed_trunc(a), tmp);
- b.full = dfixed_const(mc_latency + 512);
- c.full = dfixed_const(wm->disp_clk);
- b.full = dfixed_div(b, c);
-
- c.full = dfixed_const(dmif_size);
- b.full = dfixed_div(c, b);
-
- tmp = min(dfixed_trunc(a), dfixed_trunc(b));
-
- b.full = dfixed_const(1000);
- c.full = dfixed_const(wm->disp_clk);
- b.full = dfixed_div(c, b);
- c.full = dfixed_const(wm->bytes_per_pixel);
- b.full = dfixed_mul(b, c);
-
- lb_fill_bw = min(tmp, dfixed_trunc(b));
+ lb_fill_bw = min(tmp, wm->disp_clk * wm->bytes_per_pixel / 1000);
a.full = dfixed_const(max_src_lines_per_dst_line * wm->src_width * wm->bytes_per_pixel);
b.full = dfixed_const(1000);
--- a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c
@@ -1114,23 +1114,10 @@ static u32 dce_v11_0_latency_watermark(s
a.full = dfixed_const(available_bandwidth);
b.full = dfixed_const(wm->num_heads);
a.full = dfixed_div(a, b);
+ tmp = div_u64((u64) dmif_size * (u64) wm->disp_clk, mc_latency + 512);
+ tmp = min(dfixed_trunc(a), tmp);
- b.full = dfixed_const(mc_latency + 512);
- c.full = dfixed_const(wm->disp_clk);
- b.full = dfixed_div(b, c);
-
- c.full = dfixed_const(dmif_size);
- b.full = dfixed_div(c, b);
-
- tmp = min(dfixed_trunc(a), dfixed_trunc(b));
-
- b.full = dfixed_const(1000);
- c.full = dfixed_const(wm->disp_clk);
- b.full = dfixed_div(c, b);
- c.full = dfixed_const(wm->bytes_per_pixel);
- b.full = dfixed_mul(b, c);
-
- lb_fill_bw = min(tmp, dfixed_trunc(b));
+ lb_fill_bw = min(tmp, wm->disp_clk * wm->bytes_per_pixel / 1000);
a.full = dfixed_const(max_src_lines_per_dst_line * wm->src_width * wm->bytes_per_pixel);
b.full = dfixed_const(1000);
--- a/drivers/gpu/drm/amd/amdgpu/dce_v8_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/dce_v8_0.c
@@ -1096,23 +1096,10 @@ static u32 dce_v8_0_latency_watermark(st
a.full = dfixed_const(available_bandwidth);
b.full = dfixed_const(wm->num_heads);
a.full = dfixed_div(a, b);
+ tmp = div_u64((u64) dmif_size * (u64) wm->disp_clk, mc_latency + 512);
+ tmp = min(dfixed_trunc(a), tmp);
- b.full = dfixed_const(mc_latency + 512);
- c.full = dfixed_const(wm->disp_clk);
- b.full = dfixed_div(b, c);
-
- c.full = dfixed_const(dmif_size);
- b.full = dfixed_div(c, b);
-
- tmp = min(dfixed_trunc(a), dfixed_trunc(b));
-
- b.full = dfixed_const(1000);
- c.full = dfixed_const(wm->disp_clk);
- b.full = dfixed_div(c, b);
- c.full = dfixed_const(wm->bytes_per_pixel);
- b.full = dfixed_mul(b, c);
-
- lb_fill_bw = min(tmp, dfixed_trunc(b));
+ lb_fill_bw = min(tmp, wm->disp_clk * wm->bytes_per_pixel / 1000);
a.full = dfixed_const(max_src_lines_per_dst_line * wm->src_width * wm->bytes_per_pixel);
b.full = dfixed_const(1000);
Patches currently in stable-queue which might be from mario.kleiner.de@xxxxxxxxx are
queue-4.4/drm-amdgpu-avoid-overflows-divide-by-zero-in-latency_watermark-calculations.patch
queue-4.4/drm-amdgpu-make-display-watermark-calculations-more-accurate.patch