linux-kernel - [PATCH v2 5/5] drm/bridge: samsung-dsim: calculate porches in Hz

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Date:   Fri, 06 Oct 2023 17:07:07 +0200
From:   Michael Tretter <m.tretter@...gutronix.de>
To:     Inki Dae <inki.dae@...sung.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de, Michael Tretter <m.tretter@...gutronix.de>,
        Adam Ford <aford173@...il.com>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Marco Felsch <m.felsch@...gutronix.de>
Subject: [PATCH v2 5/5] 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@...il.com>  #imx8mm-beacon
Tested-by: Adam Ford <aford173@...il.com>  #imx8mm-beacon
Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de> # Kontron BL i.MX8MM + Waveshare 10.1inch HDMI LCD (E)
Reviewed-by: Marco Felsch <m.felsch@...gutronix.de>
Signed-off-by: Michael Tretter <m.tretter@...gutronix.de>

---
Changes in v2: None
---
 drivers/gpu/drm/bridge/samsung-dsim.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
index 714e1e833606..63a0d8dbe37c 100644
--- a/drivers/gpu/drm/bridge/samsung-dsim.c
+++ b/drivers/gpu/drm/bridge/samsung-dsim.c
@@ -986,10 +986,12 @@ 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);

-- 
2.39.2