drm/exynos/fimd: add clock rate checking

In case of some platforms fimd clocks can be configured to
very low values, as a result refresh rate can be very low and
driver/drm-core will timeout waiting for vblanks, it will result
in premature removal of framebuffers and will cause oopses.
The patch adds atomic_check callback to fimd to prevent setting
such modes.
Reported-by: NTobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: NAndrzej Hajda <a.hajda@samsung.com>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_fimd.c

@@ -198,6 +198,7 @@ struct fimd_context {
 	atomic_t			wait_vsync_event;
 	atomic_t			win_updated;
 	atomic_t			triggering;
+	u32				clkdiv;
 
 	const struct fimd_driver_data *driver_data;
 	struct drm_encoder *encoder;
@@ -389,15 +390,18 @@ static void fimd_clear_channels(struct exynos_drm_crtc *crtc)
 	pm_runtime_put(ctx->dev);
 }
 
-static u32 fimd_calc_clkdiv(struct fimd_context *ctx,
-		const struct drm_display_mode *mode)
+
+static int fimd_atomic_check(struct exynos_drm_crtc *crtc,
+		struct drm_crtc_state *state)
 {
-	unsigned long ideal_clk;
+	struct drm_display_mode *mode = &state->adjusted_mode;
+	struct fimd_context *ctx = crtc->ctx;
+	unsigned long ideal_clk, lcd_rate;
 	u32 clkdiv;
 
 	if (mode->clock == 0) {
-		DRM_ERROR("Mode has zero clock value.\n");
-		return 0xff;
+		DRM_INFO("Mode has zero clock value.\n");
+		return -EINVAL;
 	}
 
 	ideal_clk = mode->clock * 1000;
@@ -410,10 +414,23 @@ static u32 fimd_calc_clkdiv(struct fimd_context *ctx,
 		ideal_clk *= 2;
 	}
 
+	lcd_rate = clk_get_rate(ctx->lcd_clk);
+	if (2 * lcd_rate < ideal_clk) {
+		DRM_INFO("sclk_fimd clock too low(%lu) for requested pixel clock(%lu)\n",
+			 lcd_rate, ideal_clk);
+		return -EINVAL;
+	}
+
 	/* Find the clock divider value that gets us closest to ideal_clk */
-	clkdiv = DIV_ROUND_CLOSEST(clk_get_rate(ctx->lcd_clk), ideal_clk);
+	clkdiv = DIV_ROUND_CLOSEST(lcd_rate, ideal_clk);
+	if (clkdiv >= 0x200) {
+		DRM_INFO("requested pixel clock(%lu) too low\n", ideal_clk);
+		return -EINVAL;
+	}
+
+	ctx->clkdiv = (clkdiv < 0x100) ? clkdiv : 0xff;
 
-	return (clkdiv < 0x100) ? clkdiv : 0xff;
+	return 0;
 }
 
 static void fimd_setup_trigger(struct fimd_context *ctx)
@@ -442,7 +459,7 @@ static void fimd_commit(struct exynos_drm_crtc *crtc)
 	struct drm_display_mode *mode = &crtc->base.state->adjusted_mode;
 	const struct fimd_driver_data *driver_data = ctx->driver_data;
 	void *timing_base = ctx->regs + driver_data->timing_base;
-	u32 val, clkdiv;
+	u32 val;
 
 	if (ctx->suspended)
 		return;
@@ -543,9 +560,8 @@ static void fimd_commit(struct exynos_drm_crtc *crtc)
 	if (ctx->driver_data->has_clksel)
 		val |= VIDCON0_CLKSEL_LCD;
 
-	clkdiv = fimd_calc_clkdiv(ctx, mode);
-	if (clkdiv > 1)
-		val |= VIDCON0_CLKVAL_F(clkdiv - 1) | VIDCON0_CLKDIR;
+	if (ctx->clkdiv > 1)
+		val |= VIDCON0_CLKVAL_F(ctx->clkdiv - 1) | VIDCON0_CLKDIR;
 
 	writel(val, ctx->regs + VIDCON0);
 }
@@ -939,6 +955,7 @@ static const struct exynos_drm_crtc_ops fimd_crtc_ops = {
 	.update_plane = fimd_update_plane,
 	.disable_plane = fimd_disable_plane,
 	.atomic_flush = fimd_atomic_flush,
+	.atomic_check = fimd_atomic_check,
 	.te_handler = fimd_te_handler,
 };