drm: bridge: samsung-dsim: Support non-burst mode

The high-speed clock is hard-coded to the burst-clock
frequency specified in the device tree.  However, when
using devices like certain bridge chips without burst mode
and varying resolutions and refresh rates, it may be
necessary to set the high-speed clock dynamically based
on the desired pixel clock for the connected device.

This also removes the need to set a clock speed from
the device tree for non-burst mode operation, since the
pixel clock rate is the rate requested from the attached
device like a bridge chip.  This should have no impact
for people using burst-mode and setting the burst clock
rate is still required for those users.  If the burst
clock is not present, change the error message to
dev_info indicating the clock use the pixel clock.
Signed-off-by: Adam Ford <aford173@gmail.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # imx8mm-icore
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230526030559.326566-7-aford173@gmail.com

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

@@ -667,11 +667,21 @@ static unsigned long samsung_dsim_set_pll(struct samsung_dsim *dsi,
 
 static int samsung_dsim_enable_clock(struct samsung_dsim *dsi)
 {
-	unsigned long hs_clk, byte_clk, esc_clk;
+	unsigned long hs_clk, byte_clk, esc_clk, pix_clk;
 	unsigned long esc_div;
 	u32 reg;
+	struct drm_display_mode *m = &dsi->mode;
+	int bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
+
+	/* m->clock is in KHz */
+	pix_clk = m->clock * 1000;
+
+	/* Use burst_clk_rate if available, otherwise use the pix_clk */
+	if (dsi->burst_clk_rate)
+		hs_clk = samsung_dsim_set_pll(dsi, dsi->burst_clk_rate);
+	else
+		hs_clk = samsung_dsim_set_pll(dsi, DIV_ROUND_UP(pix_clk * bpp, dsi->lanes));
 
-	hs_clk = samsung_dsim_set_pll(dsi, dsi->burst_clk_rate);
 	if (!hs_clk) {
 		dev_err(dsi->dev, "failed to configure DSI PLL\n");
 		return -EFAULT;
@@ -947,7 +957,7 @@ 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->burst_clk_rate / 1000 / 8;
+		int byte_clk_khz = dsi->hs_clock / 1000 / 8;
 		int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz / m->clock;
 		int hbp = (m->htotal - m->hsync_end) * byte_clk_khz / m->clock;
 		int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz / m->clock;
@@ -1815,10 +1825,13 @@ static int samsung_dsim_parse_dt(struct samsung_dsim *dsi)
 			return PTR_ERR(pll_clk);
 	}
 
+	/* If it doesn't exist, use pixel clock instead of failing */
 	ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-frequency",
-				       &dsi->burst_clk_rate, 0);
-	if (ret < 0)
-		return ret;
+				       &dsi->burst_clk_rate, 1);
+	if (ret < 0) {
+		dev_dbg(dev, "Using pixel clock for HS clock frequency\n");
+		dsi->burst_clk_rate = 0;
+	}
 
 	ret = samsung_dsim_of_read_u32(node, "samsung,esc-clock-frequency",
 				       &dsi->esc_clk_rate, 0);