[PATCH v3] clk: zynqmp: fix compile testing without ZYNQMP_FIRMWARE

[Michal Simek <michal.simek@xilinx.com>]

When the firmware code is disabled, the incomplete error handling
in the clk driver causes compile-time warnings:

drivers/clk/zynqmp/pll.c: In function 'zynqmp_pll_recalc_rate':
drivers/clk/zynqmp/pll.c:147:29: error: 'fbdiv' is used uninitialized [-Werror=uninitialized]
  147 |         rate =  parent_rate * fbdiv;
      |                 ~~~~~~~~~~~~^~~~~~~
In function 'zynqmp_pll_get_mode',
    inlined from 'zynqmp_pll_recalc_rate' at drivers/clk/zynqmp/pll.c:148:6:
drivers/clk/zynqmp/pll.c:61:27: error: 'ret_payload' is used uninitialized [-Werror=uninitialized]
   61 |         return ret_payload[1];
      |                ~~~~~~~~~~~^~~
drivers/clk/zynqmp/pll.c: In function 'zynqmp_pll_recalc_rate':
drivers/clk/zynqmp/pll.c:53:13: note: 'ret_payload' declared here
   53 |         u32 ret_payload[PAYLOAD_ARG_CNT];
      |             ^~~~~~~~~~~
drivers/clk/zynqmp/clk-mux-zynqmp.c: In function 'zynqmp_clk_mux_get_parent':
drivers/clk/zynqmp/clk-mux-zynqmp.c:57:16: error: 'val' is used uninitialized [-Werror=uninitialized]
   57 |         return val;
      |                ^~~

As it was apparently intentional to support this for compile testing
purposes, change the code to have just enough error handling for the
compiler to not notice the remaining bugs.

Fixes: 21f237534661 ("clk: zynqmp: Drop dependency on ARCH_ZYNQMP")
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
---

Changes in v3:
- Also check PLL_MODE_ERROR return in zynqmp_pll_recalc_rate() - reported
  by Quanyang
- Change Arnd's authorhip based on our discussing at
https://lore.kernel.org/r/CAK8P3a1twOhC8DFxpLxpk8bcy0+JfGZUSE9bX4tdMetVLGTcSQ@mail.gmail.com

Changes in v2:
Based on discussion here
Link: https://lore.kernel.org/r/20210421134844.3297838-1-arnd@kernel.org
I have updated error return value which I got from clock core based on
error cases.

zynqmp_clk_mux_get_parent() should return num_parents() as error defined in
clk_core_get_parent_by_index() where num_parents is incorrect index.

Extend zynqmp_pll_get_mode() with PLL_MODE_ERROR to handle error case.

zynqmp_pll_recalc_rate() returns 0 because __clk_core_init() consider 0 as
default rate. But maybe -1ul which was used by Arnd is also good option.

---
 drivers/clk/zynqmp/clk-mux-zynqmp.c | 10 ++++++++--
 drivers/clk/zynqmp/pll.c            | 22 ++++++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/clk/zynqmp/clk-mux-zynqmp.c b/drivers/clk/zynqmp/clk-mux-zynqmp.c
index 06194149be83..d576c900dee0 100644
--- a/drivers/clk/zynqmp/clk-mux-zynqmp.c
+++ b/drivers/clk/zynqmp/clk-mux-zynqmp.c
@@ -38,7 +38,7 @@ struct zynqmp_clk_mux {
  * zynqmp_clk_mux_get_parent() - Get parent of clock
  * @hw:		handle between common and hardware-specific interfaces
  *
- * Return: Parent index
+ * Return: Parent index on success or number of parents in case of error
  */
 static u8 zynqmp_clk_mux_get_parent(struct clk_hw *hw)
 {
@@ -50,9 +50,15 @@ static u8 zynqmp_clk_mux_get_parent(struct clk_hw *hw)
 
 	ret = zynqmp_pm_clock_getparent(clk_id, &val);
 
-	if (ret)
+	if (ret) {
 		pr_warn_once("%s() getparent failed for clock: %s, ret = %d\n",
 			     __func__, clk_name, ret);
+		/*
+		 * clk_core_get_parent_by_index() takes num_parents as incorrect
+		 * index which is exactly what I want to return here
+		 */
+		return clk_hw_get_num_parents(hw);
+	}
 
 	return val;
 }
diff --git a/drivers/clk/zynqmp/pll.c b/drivers/clk/zynqmp/pll.c
index abe6afbf3407..e025581f0d54 100644
--- a/drivers/clk/zynqmp/pll.c
+++ b/drivers/clk/zynqmp/pll.c
@@ -31,8 +31,9 @@ struct zynqmp_pll {
 #define PS_PLL_VCO_MAX 3000000000UL
 
 enum pll_mode {
-	PLL_MODE_INT,
-	PLL_MODE_FRAC,
+	PLL_MODE_INT = 0,
+	PLL_MODE_FRAC = 1,
+	PLL_MODE_ERROR = 2,
 };
 
 #define FRAC_OFFSET 0x8
@@ -54,9 +55,11 @@ static inline enum pll_mode zynqmp_pll_get_mode(struct clk_hw *hw)
 	int ret;
 
 	ret = zynqmp_pm_get_pll_frac_mode(clk_id, ret_payload);
-	if (ret)
+	if (ret) {
 		pr_warn_once("%s() PLL get frac mode failed for %s, ret = %d\n",
 			     __func__, clk_name, ret);
+		return PLL_MODE_ERROR;
+	}
 
 	return ret_payload[1];
 }
@@ -126,7 +129,7 @@ static long zynqmp_pll_round_rate(struct clk_hw *hw, unsigned long rate,
  * @hw:			Handle between common and hardware-specific interfaces
  * @parent_rate:	Clock frequency of parent clock
  *
- * Return: Current clock frequency
+ * Return: Current clock frequency or 0 in case of error
  */
 static unsigned long zynqmp_pll_recalc_rate(struct clk_hw *hw,
 					    unsigned long parent_rate)
@@ -138,14 +141,21 @@ static unsigned long zynqmp_pll_recalc_rate(struct clk_hw *hw,
 	unsigned long rate, frac;
 	u32 ret_payload[PAYLOAD_ARG_CNT];
 	int ret;
+	enum pll_mode mode;
 
 	ret = zynqmp_pm_clock_getdivider(clk_id, &fbdiv);
-	if (ret)
+	if (ret) {
 		pr_warn_once("%s() get divider failed for %s, ret = %d\n",
 			     __func__, clk_name, ret);
+		return 0ul;
+	}
+
+	mode = zynqmp_pll_get_mode(hw);
+	if (mode == PLL_MODE_ERROR)
+		return 0ul;
 
 	rate =  parent_rate * fbdiv;
-	if (zynqmp_pll_get_mode(hw) == PLL_MODE_FRAC) {
+	if (mode == PLL_MODE_FRAC) {
 		zynqmp_pm_get_pll_frac_data(clk_id, ret_payload);
 		data = ret_payload[1];
 		frac = (parent_rate * data) / FRAC_DIV;
-- 
2.32.0