opp: Use clk_get_optional() to avoid leaving opp_table->clk as an error pointer

_update_opp_table_clk() uses clk_get(dev, NULL) to acquire the
device's clock. On platforms where the perf domain device has no
Linux clock and is instead managed entirely by firmware via
devm_pm_opp_of_add_table() (through
of_genpd_add_provider_simple()/onecell()), clk_get() returns
-ENOENT. That case is treated as valid (the OPP table can still
have entries sourced from firmware), but opp_table->clk is left
holding ERR_PTR(-ENOENT) rather than being reset to NULL:

	opp_table->clk = clk_get(dev, NULL);
	ret = PTR_ERR_OR_ZERO(opp_table->clk);
	...
	if (ret == -ENOENT) {
		opp_table->clk_count = 1;
		return opp_table;   /* opp_table->clk is still ERR_PTR(-ENOENT) */
	}

Consumers that only check IS_ERR(opp_table->clk) treat this as a
valid clk and pass it straight into the clk consumer API. In
particular, dev_pm_opp_set_rate() calls
clk_round_rate(opp_table->clk, target_freq), and clk_round_rate()
only guards against a NULL clk, so it dereferences the error pointer
to read clk->exclusive_count and crashes:

  Unable to handle kernel NULL pointer dereference at virtual
  address 000000000000002e
  ...
  pc : clk_round_rate+0x3c/0x188
  ...
  Call trace:
   clk_round_rate+0x3c/0x188 (P)
   dev_pm_opp_set_rate+0x114/0x33c

Rather than teaching every clk consumer API to special-case
ERR_PTR(-ENOENT), fix it at the source: use clk_get_optional()
instead of clk_get() in _update_opp_table_clk(), which already
translates -ENOENT into a NULL clk. This documents that the clock is
genuinely optional for such devices, and keeps opp_table->clk holding
either a valid clk or NULL, never a lingering -ENOENT error pointer.
_opp_config_clk_single() is only wired up via opp_table->config_clks
when a clk was actually found, and every other opp_table->clk
consumer already tolerates NULL through the standard clk API (which
treats a NULL clk as a no-op), so no other call site needs to change.

Suggested-by: Sebastian Reichel <sre@kernel.org>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Praveen Talari <praveen.talari@oss.qualcomm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/core.c

@@ -1581,8 +1581,6 @@ static struct opp_table *_update_opp_table_clk(struct device *dev,
 					       struct opp_table *opp_table,
 					       bool getclk)
 {
-	int ret;
-
 	/*
 	 * Return early if we don't need to get clk or we have already done it
 	 * earlier.
@@ -1591,39 +1589,35 @@ static struct opp_table *_update_opp_table_clk(struct device *dev,
 	    opp_table->clks)
 		return opp_table;
 
-	/* Find clk for the device */
-	opp_table->clk = clk_get(dev, NULL);
+	/*
+	 * There are few platforms which don't want the OPP core to manage
+	 * device's clock settings. In such cases neither the platform
+	 * provides the clks explicitly to us, nor the DT contains a valid
+	 * clk entry. The OPP nodes in DT may still contain "opp-hz" property
+	 * though, which we need to parse and allow the platform to find an
+	 * OPP based on freq later on.
+	 *
+	 * This is a simple solution to take care of such corner cases, i.e.
+	 * make the clk_count 1, which lets us allocate space for frequency
+	 * in opp->rates and also parse the entries in DT. Use
+	 * clk_get_optional() instead of clk_get() so opp_table->clk stays
+	 * NULL for such devices, instead of holding an ERR_PTR(-ENOENT) that
+	 * consumers must remember to special-case.
+	 */
+	opp_table->clk = clk_get_optional(dev, NULL);
 
-	ret = PTR_ERR_OR_ZERO(opp_table->clk);
-	if (!ret) {
+	if (IS_ERR(opp_table->clk)) {
+		dev_pm_opp_put_opp_table(opp_table);
+		dev_err_probe(dev, PTR_ERR(opp_table->clk), "Couldn't find clock\n");
+		return ERR_CAST(opp_table->clk);
+	}
+
+	if (opp_table->clk)
 		opp_table->config_clks = _opp_config_clk_single;
-		opp_table->clk_count = 1;
-		return opp_table;
-	}
 
-	if (ret == -ENOENT) {
-		/*
-		 * There are few platforms which don't want the OPP core to
-		 * manage device's clock settings. In such cases neither the
-		 * platform provides the clks explicitly to us, nor the DT
-		 * contains a valid clk entry. The OPP nodes in DT may still
-		 * contain "opp-hz" property though, which we need to parse and
-		 * allow the platform to find an OPP based on freq later on.
-		 *
-		 * This is a simple solution to take care of such corner cases,
-		 * i.e. make the clk_count 1, which lets us allocate space for
-		 * frequency in opp->rates and also parse the entries in DT.
-		 */
-		opp_table->clk_count = 1;
+	opp_table->clk_count = 1;
 
-		dev_dbg(dev, "%s: Couldn't find clock: %d\n", __func__, ret);
-		return opp_table;
-	}
-
-	dev_pm_opp_put_opp_table(opp_table);
-	dev_err_probe(dev, ret, "Couldn't find clock\n");
-
-	return ERR_PTR(ret);
+	return opp_table;
 }
 
 /*