Re: [PATCH net v3 1/4] dpll: zl3073x: reject output frequencies with too small divisor

The output divider has to be at least 2. In N-pin divide mode the
per-output divider must be 2 or more and the N-pin is divided once more
(also by 2 or more), so the N-pin needs an effective divisor of at least
4.

zl3073x_pin_check_freq() only checked that an output frequency divides the
synth frequency, so it accepted frequencies that would require a smaller
divisor. Reject them: require a divisor of at least 2 for normal outputs
and the P-pin of N-divided outputs, and 4 for the N-pin. Also reject a
zero frequency, which would otherwise divide by zero.

Fixes: a99a9f0ebdaa ("dpll: zl3073x: Read DPLL types and pin properties from system firmware")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
  drivers/dpll/zl3073x/prop.c | 29 ++++++++++++++++++++++-------
  1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/dpll/zl3073x/prop.c b/drivers/dpll/zl3073x/prop.c
index ac9d41d0f978..a4bdc3878590 100644
--- a/drivers/dpll/zl3073x/prop.c
+++ b/drivers/dpll/zl3073x/prop.c

@@ -22,7 +22,8 @@
   * The function checks the given frequency is valid for the device. For input
   * pins it checks that the frequency can be factorized using supported base
   * frequencies. For output pins it checks that the frequency divides connected
- * synth frequency without remainder.
+ * synth frequency without remainder and that the resulting divisor is within
+ * the range supported by the hardware.
   *
   * Return: true if the frequency is valid, false if not.
   */

@@ -30,7 +31,7 @@ static bool
  zl3073x_pin_check_freq(struct zl3073x_dev *zldev, enum dpll_pin_direction dir,
  		       u8 id, u64 freq)
  {
-	if (freq > U32_MAX)
+	if (!freq || freq > U32_MAX)
  		goto err_inv_freq;
  
  	if (dir == DPLL_PIN_DIRECTION_INPUT) {

@@ -41,18 +42,32 @@ zl3073x_pin_check_freq(struct zl3073x_dev *zldev, enum dpll_pin_direction dir,
  		if (rc)
  			goto err_inv_freq;
  	} else {
-		u32 synth_freq;
-		u8 out, synth;
+		const struct zl3073x_out *out;
+		u32 synth_freq, div, min_div, rem;
+		u8 out_id, synth;
  
  		/* Get output pin synthesizer */
-		out = zl3073x_output_pin_out_get(id);
-		synth = zl3073x_dev_out_synth_get(zldev, out);
+		out_id = zl3073x_output_pin_out_get(id);
+		synth = zl3073x_dev_out_synth_get(zldev, out_id);
  
  		/* Get synth frequency */
  		synth_freq = zl3073x_dev_synth_freq_get(zldev, synth);
  
  		/* Check the frequency divides synth frequency */
-		if (synth_freq % (u32)freq)
+		div = div_u64_rem(synth_freq, freq, &rem);
+		if (rem)
+			goto err_inv_freq;
+
+		/* The output divisor has to be at least 2. For the N-pin of an
+		 * N-divided output the effective divisor also includes the N
+		 * divider (>= 2), so the minimum is 4.
+		 */
+		out = zl3073x_out_state_get(zldev, out_id);
+		if (zl3073x_out_is_ndiv(out) && zl3073x_is_n_pin(id))
+			min_div = 4;
+		else
+			min_div = 2;
+		if (div < min_div)
  			goto err_inv_freq;
  	}