drm/bridge: samsung-dsim: calculate porches in Hz

Calculating the byte_clk in kHz is imprecise for a hs_clock of 55687500
Hz, which may be used with a pixel clock of 74.25 MHz with mode
1920x1080-30.

Fix the calculation by using HZ instead of kHZ.

This requires to change the type to u64 to prevent overflows of the
integer type.

Reviewed-by: Adam Ford <aford173@gmail.com>  #imx8mm-beacon
Tested-by: Adam Ford <aford173@gmail.com>  #imx8mm-beacon
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de> # Kontron BL i.MX8MM + Waveshare 10.1inch HDMI LCD (E)
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20230818-samsung-dsim-v2-5-846603df0e0a@pengutronix.deSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230818-samsung-dsim-v2-5-846603df0e0a@pengutronix.de

drivers/gpu/drm/bridge/samsung-dsim.c

@@ -988,10 +988,12 @@ static void samsung_dsim_set_display_mode(struct samsung_dsim *dsi)
 	u32 reg;
 
 	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
-		int byte_clk_khz = dsi->hs_clock / 1000 / 8;
-		int hfp = DIV_ROUND_UP((m->hsync_start - m->hdisplay) * byte_clk_khz, m->clock);
-		int hbp = DIV_ROUND_UP((m->htotal - m->hsync_end) * byte_clk_khz, m->clock);
-		int hsa = DIV_ROUND_UP((m->hsync_end - m->hsync_start) * byte_clk_khz, m->clock);
+		u64 byte_clk = dsi->hs_clock / 8;
+		u64 pix_clk = m->clock * 1000;
+
+		int hfp = DIV64_U64_ROUND_UP((m->hsync_start - m->hdisplay) * byte_clk, pix_clk);
+		int hbp = DIV64_U64_ROUND_UP((m->htotal - m->hsync_end) * byte_clk, pix_clk);
+		int hsa = DIV64_U64_ROUND_UP((m->hsync_end - m->hsync_start) * byte_clk, pix_clk);
 
 		/* remove packet overhead when possible */
 		hfp = max(hfp - 6, 0);