linux-kernel - [PATCH RESEND v2 4/5] clk: mxl: Add validation for register reads/writes

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Date:   Thu, 22 Sep 2022 14:24:27 +0800
From:   Rahul Tanwar <rtanwar@...linear.com>
To:     <sboyd@...nel.org>, <mturquette@...libre.com>,
        <linux-clk@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-lgm-soc@...linear.com>,
        "Rahul Tanwar" <rtanwar@...linear.com>
Subject: [PATCH RESEND v2 4/5] clk: mxl: Add validation for register reads/writes

Some clocks support parent clock dividers but they do not
support clock gating (clk enable/disable). Such types of
clocks might call API's for get/set_reg_val routines with
width as 0 during clk_prepare_enable() call. Handle such
cases by first validating width during clk_prepare_enable()
while still supporting clk_set_rate() correctly.

Signed-off-by: Rahul Tanwar <rtanwar@...linear.com>
---
 drivers/clk/x86/clk-cgu.h | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/x86/clk-cgu.h b/drivers/clk/x86/clk-cgu.h
index 73ce84345f81..46daf9ebd6c9 100644
--- a/drivers/clk/x86/clk-cgu.h
+++ b/drivers/clk/x86/clk-cgu.h
@@ -299,29 +299,51 @@ struct lgm_clk_branch {
 static inline void lgm_set_clk_val(struct regmap *membase, u32 reg,
 				   u8 shift, u8 width, u32 set_val)
 {
-	u32 mask = (GENMASK(width - 1, 0) << shift);
+	u32 mask;
 
+	/*
+	 * Some clocks support parent clock dividers but they do not
+	 * support clock gating (clk enable/disable). Such types of
+	 * clocks might call this function with width as 0 during
+	 * clk_prepare_enable() call. Handle such cases by not doing
+	 * anything during clk_prepare_enable() but handle clk_set_rate()
+	 * correctly
+	 */
+	if (!width)
+		return;
+
+	mask = (GENMASK(width - 1, 0) << shift);
 	regmap_update_bits(membase, reg, mask, set_val << shift);
 }
 
 static inline u32 lgm_get_clk_val(struct regmap *membase, u32 reg,
 				  u8 shift, u8 width)
 {
-	u32 mask = (GENMASK(width - 1, 0) << shift);
+	u32 mask;
 	u32 val;
 
+	/*
+	 * Some clocks support parent clock dividers but they do not
+	 * support clock gating (clk enable/disable). Such types of
+	 * clocks might call this function with width as 0 during
+	 * clk_prepare_enable() call. Handle such cases by not doing
+	 * anything during clk_prepare_enable() but handle clk_set_rate()
+	 * correctly
+	 */
+	if (!width)
+		return 0;
+
 	if (regmap_read(membase, reg, &val)) {
 		WARN_ONCE(1, "Failed to read clk reg: 0x%x\n", reg);
 		return 0;
 	}
 
+	mask = (GENMASK(width - 1, 0) << shift);
 	val = (val & mask) >> shift;
 
 	return val;
 }
 
-
-
 int lgm_clk_register_branches(struct lgm_clk_provider *ctx,
 			      const struct lgm_clk_branch *list,
 			      unsigned int nr_clk);
-- 
2.17.1