linux-kernel - [PATCH] drm/amd/display: fix 64-bit integer division

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Message-Id: <20210225143339.3693838-1-arnd@kernel.org>
Date:   Thu, 25 Feb 2021 15:33:10 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Bindu Ramamurthy <bindu.r@....com>,
        Vladimir Stempen <vladimir.stempen@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Dmytro Laktyushkin <Dmytro.Laktyushkin@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/amd/display: fix 64-bit integer division

From: Arnd Bergmann <arnd@...db.de>

The new display synchronization code caused a regression
on all 32-bit architectures:

ld.lld: error: undefined symbol: __aeabi_uldivmod
>>> referenced by dce_clock_source.c
>>>               gpu/drm/amd/display/dc/dce/dce_clock_source.o:(get_pixel_clk_frequency_100hz) in archive drivers/built-in.a

ld.lld: error: undefined symbol: __aeabi_ldivmod
>>> referenced by dc_resource.c
>>>               gpu/drm/amd/display/dc/core/dc_resource.o:(resource_are_vblanks_synchronizable) in archive drivers/built-in.a
>>> referenced by dc_resource.c
>>>               gpu/drm/amd/display/dc/core/dc_resource.o:(resource_are_vblanks_synchronizable) in archive drivers/built-in.a
>>> referenced by dc_resource.c
>>>               gpu/drm/amd/display/dc/core/dc_resource.o:(resource_are_vblanks_synchronizable) in archive drivers/built-in.a

This is not a fast path, so the use of an explicit div_u64/div_s64
seems appropriate.

Fixes: 77a2b7265f20 ("drm/amd/display: Synchronize displays with different timings")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/amd/display/dc/core/dc_resource.c    | 12 ++++++------
 .../gpu/drm/amd/display/dc/dce/dce_clock_source.c    |  6 +++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
index 0241c9d96d7a..49214c59c836 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
@@ -441,15 +441,15 @@ bool resource_are_vblanks_synchronizable(
 		if (stream2->timing.pix_clk_100hz*100/stream2->timing.h_total/
 				stream2->timing.v_total > 60)
 			return false;
-		frame_time_diff = (int64_t)10000 *
+		frame_time_diff = div_s64(10000ll *
 			stream1->timing.h_total *
 			stream1->timing.v_total *
-			stream2->timing.pix_clk_100hz /
-			stream1->timing.pix_clk_100hz /
-			stream2->timing.h_total /
-			stream2->timing.v_total;
+			stream2->timing.pix_clk_100hz,
+			stream1->timing.pix_clk_100hz *
+			stream2->timing.h_total *
+			stream2->timing.v_total);
 		for (i = 0; i < rr_count; i++) {
-			int64_t diff = (frame_time_diff * base60_refresh_rates[i]) / 10 - 10000;
+			int64_t diff = div_s64(frame_time_diff * base60_refresh_rates[i], 10) - 10000;
 
 			if (diff < 0)
 				diff = -diff;
diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
index 6f47f9bab5ee..85ed6f2c9647 100644
--- a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
+++ b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
@@ -1013,9 +1013,9 @@ static bool get_pixel_clk_frequency_100hz(
 			 * not be programmed equal to DPREFCLK
 			 */
 			modulo_hz = REG_READ(MODULO[inst]);
-			*pixel_clk_khz = ((uint64_t)clock_hz*
-				clock_source->ctx->dc->clk_mgr->dprefclk_khz*10)/
-				modulo_hz;
+			*pixel_clk_khz = div_u64((uint64_t)clock_hz * 10 *
+				clock_source->ctx->dc->clk_mgr->dprefclk_khz,
+				modulo_hz);
 		} else {
 			/* NOTE: There is agreement with VBIOS here that MODULO is
 			 * programmed equal to DPREFCLK, in which case PHASE will be
-- 
2.29.2