[PATCH] drm/amd/display: avoid 64-bit division

From: Arnd Bergmann <arnd@arndb.de>
To: "Harry Wentland" <harry.wentland@amd.com>,
	"Leo Li" <sunpeng.li@amd.com>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Christian König" <christian.koenig@amd.com>,
	"David (ChunMing) Zhou" <David1.Zhou@amd.com>,
	"David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel@ffwll.ch>
Cc: Charlene Liu <Charlene.Liu@amd.com>,
	Chris Park <Chris.Park@amd.com>, Arnd Bergmann <arnd@arndb.de>,
	Tony Cheng <tony.cheng@amd.com>,
	David Francis <David.Francis@amd.com>,
	linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org,
	Nikola Cornij <nikola.cornij@amd.com>,
	Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>,
	dri-devel@lists.freedesktop.org, Jun Lei <Jun.Lei@amd.com>,
	Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>,
	Anthony Koo <Anthony.Koo@amd.com>
Subject: [PATCH] drm/amd/display: avoid 64-bit division
Date: Mon,  8 Jul 2019 15:52:08 +0200	[thread overview]
Message-ID: <20190708135238.651483-1-arnd@arndb.de> (raw)

On 32-bit architectures, dividing a 64-bit integer in the kernel
leads to a link error:

ERROR: "__udivdi3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
ERROR: "__divdi3" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!

Change the two recently introduced instances to a multiply+shift
operation that is also much cheaper on 32-bit architectures.
We can do that here, since both of them are really 32-bit numbers
that change a few percent.

Fixes: bedbbe6af4be ("drm/amd/display: Move link functions from dc to dc_link")
Fixes: f18bc4e53ad6 ("drm/amd/display: update calculated bounding box logic for NV")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c         | 4 ++--
 drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index c17db5c144aa..8dbf759eba45 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -3072,8 +3072,8 @@ uint32_t dc_link_bandwidth_kbps(
 		 * but the difference is minimal and is in a safe direction,
 		 * which all works well around potential ambiguity of DP 1.4a spec.
 		 */
-		long long fec_link_bw_kbps = link_bw_kbps * 970LL;
-		link_bw_kbps = (uint32_t)(fec_link_bw_kbps / 1000LL);
+		link_bw_kbps = mul_u64_u32_shr(BIT_ULL(32) * 970LL / 1000,
+					       link_bw_kbps, 32);
 	}
 #endif
 
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
index b35327bafbc5..70ac8a95d2db 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
@@ -2657,7 +2657,7 @@ static void update_bounding_box(struct dc *dc, struct _vcs_dpi_soc_bounding_box_
 		calculated_states[i].dram_speed_mts = uclk_states[i] * 16 / 1000;
 
 		// FCLK:UCLK ratio is 1.08
-		min_fclk_required_by_uclk = ((unsigned long long)uclk_states[i]) * 1080 / 1000000;
+		min_fclk_required_by_uclk = mul_u64_u32_shr(BIT_ULL(32) * 1080 / 1000000, uclk_states[i], 32);
 
 		calculated_states[i].fabricclk_mhz = (min_fclk_required_by_uclk < min_dcfclk) ?
 				min_dcfclk : min_fclk_required_by_uclk;
-- 
2.20.0

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