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

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

64-bit division is costly on 32-bit targets and should be avoided:

x86_64-linux-ld: drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.o: in function `get_dp_dto_frequency_100hz':
dce_clock_source.c:(.text+0x407): undefined reference to `__udivdi3'
x86_64-linux-ld: drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.o: in function `dcn401_get_dp_dto_frequency_100hz':
dce_clock_source.c:(.text+0x8b8): undefined reference to `__udivdi3'

Replace the open-coded division with a div_u64() call where necessary.
This could be done in a more clever way using mul_u64_u32_shr()
or similar, but since this is called rarely, use the most readable
variant that works.

Fixes: 6f6483dbfacd ("drm/amd/display: Update get_pixel_clk_frequency() for DCN4x DCCG DP DTO")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

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 7c293917e6fd..501ab1a3bac2 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
@@ -1229,9 +1229,9 @@ static bool get_dp_dto_frequency_100hz(
 			 */
 			modulo_hz = REG_READ(MODULO[inst]);
 			if (modulo_hz) {
-				temp = div_u64((uint64_t)clock_hz * dp_dto_ref_khz * 10, modulo_hz);
-				ASSERT(temp / 100 <= 0xFFFFFFFFUL);
-				*pixel_clk_100hz = (unsigned int)(temp / 100);
+				temp = clock_hz * dp_dto_ref_khz * 10;
+				ASSERT(temp <= INT_MAX * modulo_hz * 100);
+				*pixel_clk_100hz = div_u64(temp, modulo_hz * 100);
 			} else
 				*pixel_clk_100hz = 0;
 		} else {
@@ -1286,12 +1286,12 @@ static bool dcn401_get_dp_dto_frequency_100hz(const struct clock_source *clock_s
 		 */
 		temp = (unsigned long long)dp_dto_integer * modulo_hz + phase_hz;
 
-		if (temp / 100 > 0xFFFFFFFFUL) {
+		if (temp > (UINT_MAX * 100ULL)) {
 			/* pixel rate 100hz should never be this high, if it is, throw an assert and return 0  */
 			BREAK_TO_DEBUGGER();
 			*pixel_clk_100hz = 0;
 		} else {
-			*pixel_clk_100hz = (unsigned int)(temp / 100);
+			*pixel_clk_100hz = div_u64(temp, 100);
 		}
 
 		return true;
-- 
2.39.5