gpu: ipu-v3: limit pixel clock divider to 8-bits

The DI pixel clock divider bit field is only 8 bits wide for the
integer part, so limit the divider to the 1...255 interval before
deciding whether the internal clock can be used and before writing
to the register.
Reported-by: Felix Mellmann <felix.mellmann@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/ipu-v3/ipu-di.c

@@ -441,8 +441,7 @@ static void ipu_di_config_clock(struct ipu_di *di,
 
 			in_rate = clk_get_rate(clk);
 			div = DIV_ROUND_CLOSEST(in_rate, sig->mode.pixelclock);
-			if (div == 0)
-				div = 1;
+			div = clamp(div, 1U, 255U);
 
 			clkgen0 = div << 4;
 		}
@@ -459,8 +458,7 @@ static void ipu_di_config_clock(struct ipu_di *di,
 
 		clkrate = clk_get_rate(di->clk_ipu);
 		div = DIV_ROUND_CLOSEST(clkrate, sig->mode.pixelclock);
-		if (div == 0)
-			div = 1;
+		div = clamp(div, 1U, 255U);
 		rate = clkrate / div;
 
 		error = rate / (sig->mode.pixelclock / 1000);
@@ -483,8 +481,7 @@ static void ipu_di_config_clock(struct ipu_di *di,
 
 			in_rate = clk_get_rate(clk);
 			div = DIV_ROUND_CLOSEST(in_rate, sig->mode.pixelclock);
-			if (div == 0)
-				div = 1;
+			div = clamp(div, 1U, 255U);
 
 			clkgen0 = div << 4;
 		}