[PATCH net-next v8 09/15] dpll: sit9531x: implement output pin state on a DPLL

[Ali Rouhi <arouhi@sitime.com>]

From: Oleg Zadorozhnyi <Oleg.Zadorozhnyi@devoxsoftware.com>

An output is driven by its PLL rather than selected by it, so its state
says whether it carries a signal: connected while it drives, disconnected
while it is muted.  Setting the state mutes or un-mutes it by forcing the
pad to Hi-Z, the only per-output control the device offers that leaves the
divider alone.

The force bit and the state bit are separate, and a pad follows the loaded
configuration while the force bit is clear, so both are read to decide
whether an output is muted and both are written to change it.  Which of
the four register banks applies depends on the slot and on whether the pad
is single-ended or differential.

Signed-off-by: Oleg Zadorozhnyi <Oleg.Zadorozhnyi@devoxsoftware.com>
Assisted-by: Claude:claude-4-opus [chat]
Signed-off-by: Ali Rouhi <arouhi@sitime.com>
---
 drivers/dpll/sit9531x/core.c | 143 +++++++++++++++++++++++++++++++++++
 drivers/dpll/sit9531x/dpll.c |  69 +++++++++++++++++
 2 files changed, 212 insertions(+)

diff --git a/drivers/dpll/sit9531x/core.c b/drivers/dpll/sit9531x/core.c
index 721b2c451d59..0f886cfd1401 100644
--- a/drivers/dpll/sit9531x/core.c
+++ b/drivers/dpll/sit9531x/core.c
@@ -339,6 +339,40 @@ static int sit9531x_output_forced_hiz(struct sit9531x_dev *sitdev, u8 slot,
 	return 0;
 }
 
+static int sit9531x_hiz_set_bit(struct sit9531x_dev *sitdev,
+				unsigned int reg, u8 bit, bool set)
+{
+	u8 cur, new_val;
+	int rc;
+
+	rc = sit9531x_read_u8(sitdev, reg, &cur);
+	if (rc)
+		return rc;
+
+	new_val = set ? (cur | BIT(bit)) : (cur & ~BIT(bit));
+
+	return sit9531x_write_u8(sitdev, reg, new_val);
+}
+
+/*
+ * Enter the output-system programming state: unlock the debug
+ * registers on Page 3 and issue the PRG_CMD state command.  Register
+ * writes that reconfigure the output system only take effect when
+ * they are made inside this state.
+ */
+static int sit9531x_prg_enter(struct sit9531x_dev *sitdev)
+{
+	int rc;
+
+	rc = sit9531x_write_u8(sitdev, SIT9531X_REG_OUTSYS_DEBUG,
+			       SIT9531X_DEBUG_UNLOCK_VAL);
+	if (rc)
+		return rc;
+
+	return sit9531x_write_u8(sitdev, SIT9531X_REG_PRG_DIR_GEN,
+				 SIT9531X_PRG_CMD_STATE);
+}
+
 /*
  * Commit a programming sequence started by sit9531x_prg_enter():
  * update the NVM shadow and re-lock the loops.  The sleep gives the
@@ -368,6 +402,115 @@ static int sit9531x_prg_commit(struct sit9531x_dev *sitdev)
 	return rc ? rc : rc2;
 }
 
+/*
+ * sit9531x_output_disable - mute an output (force Hi-Z)
+ * @index:	logical output index (0..info->num_outputs-1)
+ *
+ * Sets MASK+STATE on BOTH the DIFF and SE register pairs so that the
+ * output is muted regardless of its electrical configuration.  The
+ * writes are wrapped in the PRG_CMD / NVM update / loop lock sequence
+ * so the new state is applied by the hardware.
+ *
+ * Caller must hold sitdev->multiop_lock.
+ */
+int sit9531x_output_disable(struct sit9531x_dev *sitdev, u8 index)
+{
+	const struct sit9531x_chip_info *info = sitdev->info;
+	struct sit9531x_hiz_regs r;
+	u8 slot;
+	int rc, ret;
+
+	lockdep_assert_held(&sitdev->multiop_lock);
+
+	if (index >= info->num_outputs)
+		return -EINVAL;
+
+	slot = info->clkout_map[index];
+	sit9531x_output_get_hiz_regs(slot, &r);
+
+	rc = sit9531x_prg_enter(sitdev);
+	if (rc)
+		return rc;
+
+	/* Take control (MASK=1) and mute (STATE=0) on both DIFF and SE */
+	rc = sit9531x_hiz_set_bit(sitdev, r.diff_mask, r.bit, true);
+	if (rc)
+		goto commit;
+	rc = sit9531x_hiz_set_bit(sitdev, r.diff_state, r.bit, false);
+	if (rc)
+		goto commit;
+	rc = sit9531x_hiz_set_bit(sitdev, r.se_mask, r.bit, true);
+	if (rc)
+		goto commit;
+	rc = sit9531x_hiz_set_bit(sitdev, r.se_state, r.bit, false);
+
+commit:
+	/*
+	 * Always leave the PRG_CMD programming state, even on a mid-sequence
+	 * write failure: prg_enter() unlocked the output loops, so returning
+	 * without prg_commit() would strand the chip in the programming state
+	 * with the loops unlocked.  Best effort -- keep the first error.
+	 */
+	ret = sit9531x_prg_commit(sitdev);
+	if (ret && !rc)
+		rc = ret;
+	if (!rc)
+		sitdev->out[index].enabled = false;
+
+	return rc;
+}
+
+/*
+ * sit9531x_output_enable - un-mute an output (active state)
+ * @index:	logical output index (0..info->num_outputs-1)
+ *
+ * Releases MASK on BOTH register pairs so the output returns to
+ * whatever the initial_config blob programmed.  The writes are wrapped
+ * in the PRG_CMD / NVM update / loop lock sequence so the new state is
+ * applied by the hardware.
+ *
+ * Caller must hold sitdev->multiop_lock.
+ */
+int sit9531x_output_enable(struct sit9531x_dev *sitdev, u8 index)
+{
+	const struct sit9531x_chip_info *info = sitdev->info;
+	struct sit9531x_hiz_regs r;
+	u8 slot;
+	int rc, ret;
+
+	lockdep_assert_held(&sitdev->multiop_lock);
+
+	if (index >= info->num_outputs)
+		return -EINVAL;
+
+	slot = info->clkout_map[index];
+	sit9531x_output_get_hiz_regs(slot, &r);
+
+	rc = sit9531x_prg_enter(sitdev);
+	if (rc)
+		return rc;
+
+	rc = sit9531x_hiz_set_bit(sitdev, r.diff_mask, r.bit, false);
+	if (rc)
+		goto commit;
+	rc = sit9531x_hiz_set_bit(sitdev, r.se_mask, r.bit, false);
+
+commit:
+	/*
+	 * Always leave the PRG_CMD programming state, even on a mid-sequence
+	 * write failure: prg_enter() unlocked the output loops, so returning
+	 * without prg_commit() would strand the chip in the programming state
+	 * with the loops unlocked.  Best effort -- keep the first error.
+	 */
+	ret = sit9531x_prg_commit(sitdev);
+	if (ret && !rc)
+		rc = ret;
+	if (!rc)
+		sitdev->out[index].enabled = true;
+
+	return rc;
+}
+
 /*
  * Input priority selection
  *
diff --git a/drivers/dpll/sit9531x/dpll.c b/drivers/dpll/sit9531x/dpll.c
index a7510ca721b6..6365a83e4c52 100644
--- a/drivers/dpll/sit9531x/dpll.c
+++ b/drivers/dpll/sit9531x/dpll.c
@@ -669,10 +669,79 @@ sit9531x_dpll_output_pin_frequency_set(const struct dpll_pin *pin,
 	return rc;
 }
 
+/*
+ * sit9531x_dpll_output_pin_state_on_dpll_get - get output pin state
+ *
+ * reports CONNECTED when the output is driven and
+ * DISCONNECTED when it has been muted via sit9531x_output_disable().
+ */
+static int
+sit9531x_dpll_output_pin_state_on_dpll_get(const struct dpll_pin *pin,
+					   void *pin_priv,
+					   const struct dpll_device *dpll,
+					   void *dpll_priv,
+					   enum dpll_pin_state *state,
+					   struct netlink_ext_ack *extack)
+{
+	struct sit9531x_dpll_pin *dpin = pin_priv;
+	struct sit9531x_dpll *sitdpll = dpll_priv;
+	const struct sit9531x_out *out;
+
+	out = sit9531x_out_state_get(sitdpll->dev, dpin->id);
+	*state = out->enabled ? DPLL_PIN_STATE_CONNECTED
+			      : DPLL_PIN_STATE_DISCONNECTED;
+	return 0;
+}
+
+/*
+ * sit9531x_dpll_output_pin_state_on_dpll_set - mute/un-mute an output
+ *
+ * forces Hi-Z on the output pin via the Page 0x03
+ * force/state register pair.
+ *   CONNECTED    -> enable (release force, back to factory default)
+ *   DISCONNECTED -> disable (force Hi-Z)
+ */
+static int
+sit9531x_dpll_output_pin_state_on_dpll_set(const struct dpll_pin *pin,
+					   void *pin_priv,
+					   const struct dpll_device *dpll,
+					   void *dpll_priv,
+					   enum dpll_pin_state state,
+					   struct netlink_ext_ack *extack)
+{
+	struct sit9531x_dpll_pin *dpin = pin_priv;
+	struct sit9531x_dpll *sitdpll = dpll_priv;
+	struct sit9531x_dev *sitdev = sitdpll->dev;
+	int rc;
+
+	mutex_lock(&sitdev->multiop_lock);
+
+	switch (state) {
+	case DPLL_PIN_STATE_CONNECTED:
+		rc = sit9531x_output_enable(sitdev, dpin->id);
+		break;
+	case DPLL_PIN_STATE_DISCONNECTED:
+		rc = sit9531x_output_disable(sitdev, dpin->id);
+		break;
+	default:
+		rc = -EINVAL;
+		break;
+	}
+
+	mutex_unlock(&sitdev->multiop_lock);
+
+	if (rc)
+		NL_SET_ERR_MSG(extack, "Failed to set output pin state");
+
+	return rc;
+}
+
 static const struct dpll_pin_ops sit9531x_dpll_output_pin_ops = {
 	.direction_get		= sit9531x_dpll_output_pin_direction_get,
 	.frequency_get		= sit9531x_dpll_output_pin_frequency_get,
 	.frequency_set		= sit9531x_dpll_output_pin_frequency_set,
+	.state_on_dpll_get	= sit9531x_dpll_output_pin_state_on_dpll_get,
+	.state_on_dpll_set	= sit9531x_dpll_output_pin_state_on_dpll_set,
 };
 
 const struct dpll_pin_ops *
-- 
2.43.0