drm/arm/hdlcd: Actually validate CRTC modes

Rather than allowing any old mode through, then subsequently refusing
unmatchable clock rates in atomic_check when it's too late to back out
and pick a different mode, let's do that validation up-front where it
will cause unsupported modes to be correctly pruned in the first place.

This also eliminates an issue whereby a perceived clock rate of 0 would
cause atomic disable to fail and prevent the module from being unloaded.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

drivers/gpu/drm/arm/hdlcd_crtc.c

@@ -186,20 +186,19 @@ static void hdlcd_crtc_atomic_disable(struct drm_crtc *crtc,
 	clk_disable_unprepare(hdlcd->clk);
 }
 
-static int hdlcd_crtc_atomic_check(struct drm_crtc *crtc,
-				   struct drm_crtc_state *state)
+static enum drm_mode_status hdlcd_crtc_mode_valid(struct drm_crtc *crtc,
+		const struct drm_display_mode *mode)
 {
 	struct hdlcd_drm_private *hdlcd = crtc_to_hdlcd_priv(crtc);
-	struct drm_display_mode *mode = &state->adjusted_mode;
 	long rate, clk_rate = mode->clock * 1000;
 
 	rate = clk_round_rate(hdlcd->clk, clk_rate);
 	if (rate != clk_rate) {
 		/* clock required by mode not supported by hardware */
-		return -EINVAL;
+		return MODE_NOCLOCK;
 	}
 
-	return 0;
+	return MODE_OK;
 }
 
 static void hdlcd_crtc_atomic_begin(struct drm_crtc *crtc,
@@ -220,7 +219,7 @@ static void hdlcd_crtc_atomic_begin(struct drm_crtc *crtc,
 }
 
 static const struct drm_crtc_helper_funcs hdlcd_crtc_helper_funcs = {
-	.atomic_check	= hdlcd_crtc_atomic_check,
+	.mode_valid	= hdlcd_crtc_mode_valid,
 	.atomic_begin	= hdlcd_crtc_atomic_begin,
 	.atomic_enable	= hdlcd_crtc_atomic_enable,
 	.atomic_disable	= hdlcd_crtc_atomic_disable,