clk: qcom: Configure the RCGs to a safe source as needed

For some root clock generators, there could be child branches which are
controlled by an entity other than application processor subsystem. For
such RCGs, as per application processor subsystem clock driver, all of
its downstream clocks are disabled and RCG is in disabled state but in
reality downstream clocks can be left enabled before.

So in this scenario, when RCG is disabled as per clock driver's point of
view and when rate scaling request comes before downstream clock enable
request, then RCG fails to update its configuration because in reality
RCG is on and it expects its new source to already be in enable state but
in reality new source is off. In order to avoid having the RCG to go into
an invalid state, add support to update the CFG, M, N and D registers
during set_rate() without configuration update and defer the actual RCG
configuration update to be done during clk_enable() as at this point of
time, both its new parent and safe source will be already enabled and RCG
can safely switch to new parent.

During clk_disable() request, configure it to safe source as both its
parents, safe source and current parent will be enabled and RCG can
safely execute a switch.
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Amit Nischal <anischal@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/qcom/clk-rcg.h

-/*
- * Copyright (c) 2013, The Linux Foundation. All rights reserved.
- *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- */
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2013, 2018, The Linux Foundation. All rights reserved. */
 
 #ifndef __QCOM_CLK_RCG_H__
 #define __QCOM_CLK_RCG_H__
@@ -144,6 +134,7 @@ extern const struct clk_ops clk_dyn_rcg_ops;
  * @cmd_rcgr: corresponds to *_CMD_RCGR
  * @mnd_width: number of bits in m/n/d values
  * @hid_width: number of bits in half integer divider
+ * @safe_src_index: safe src index value
  * @parent_map: map from software's parent index to hardware's src_sel field
  * @freq_tbl: frequency table
  * @clkr: regmap clock handle
@@ -153,6 +144,7 @@ struct clk_rcg2 {
 	u32			cmd_rcgr;
 	u8			mnd_width;
 	u8			hid_width;
+	u8			safe_src_index;
 	const struct parent_map	*parent_map;
 	const struct freq_tbl	*freq_tbl;
 	struct clk_regmap	clkr;
@@ -167,5 +159,6 @@ extern const struct clk_ops clk_byte_ops;
 extern const struct clk_ops clk_byte2_ops;
 extern const struct clk_ops clk_pixel_ops;
 extern const struct clk_ops clk_gfx3d_ops;
+extern const struct clk_ops clk_rcg2_shared_ops;
 
 #endif

drivers/clk/qcom/clk-rcg2.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2013, 2018, The Linux Foundation. All rights reserved.
- *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
  */
 
 #include <linux/kernel.h>
@@ -249,7 +241,7 @@ static int clk_rcg2_determine_floor_rate(struct clk_hw *hw,
 	return _freq_tbl_determine_rate(hw, rcg->freq_tbl, req, FLOOR);
 }
 
-static int clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
+static int __clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
 {
 	u32 cfg, mask;
 	struct clk_hw *hw = &rcg->clkr.hw;
@@ -282,8 +274,16 @@ static int clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
 	cfg |= rcg->parent_map[index].cfg << CFG_SRC_SEL_SHIFT;
 	if (rcg->mnd_width && f->n && (f->m != f->n))
 		cfg |= CFG_MODE_DUAL_EDGE;
-	ret = regmap_update_bits(rcg->clkr.regmap,
-			rcg->cmd_rcgr + CFG_REG, mask, cfg);
+
+	return regmap_update_bits(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG,
+					mask, cfg);
+}
+
+static int clk_rcg2_configure(struct clk_rcg2 *rcg, const struct freq_tbl *f)
+{
+	int ret;
+
+	ret = __clk_rcg2_configure(rcg, f);
 	if (ret)
 		return ret;
 
@@ -790,3 +790,141 @@ const struct clk_ops clk_gfx3d_ops = {
 	.determine_rate = clk_gfx3d_determine_rate,
 };
 EXPORT_SYMBOL_GPL(clk_gfx3d_ops);
+
+static int clk_rcg2_set_force_enable(struct clk_hw *hw)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+	const char *name = clk_hw_get_name(hw);
+	int ret, count;
+
+	ret = regmap_update_bits(rcg->clkr.regmap, rcg->cmd_rcgr + CMD_REG,
+				 CMD_ROOT_EN, CMD_ROOT_EN);
+	if (ret)
+		return ret;
+
+	/* wait for RCG to turn ON */
+	for (count = 500; count > 0; count--) {
+		if (clk_rcg2_is_enabled(hw))
+			return 0;
+
+		udelay(1);
+	}
+
+	pr_err("%s: RCG did not turn on\n", name);
+	return -ETIMEDOUT;
+}
+
+static int clk_rcg2_clear_force_enable(struct clk_hw *hw)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+
+	return regmap_update_bits(rcg->clkr.regmap, rcg->cmd_rcgr + CMD_REG,
+					CMD_ROOT_EN, 0);
+}
+
+static int
+clk_rcg2_shared_force_enable_clear(struct clk_hw *hw, const struct freq_tbl *f)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+	int ret;
+
+	ret = clk_rcg2_set_force_enable(hw);
+	if (ret)
+		return ret;
+
+	ret = clk_rcg2_configure(rcg, f);
+	if (ret)
+		return ret;
+
+	return clk_rcg2_clear_force_enable(hw);
+}
+
+static int clk_rcg2_shared_set_rate(struct clk_hw *hw, unsigned long rate,
+				    unsigned long parent_rate)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+	const struct freq_tbl *f;
+
+	f = qcom_find_freq(rcg->freq_tbl, rate);
+	if (!f)
+		return -EINVAL;
+
+	/*
+	 * In case clock is disabled, update the CFG, M, N and D registers
+	 * and don't hit the update bit of CMD register.
+	 */
+	if (!__clk_is_enabled(hw->clk))
+		return __clk_rcg2_configure(rcg, f);
+
+	return clk_rcg2_shared_force_enable_clear(hw, f);
+}
+
+static int clk_rcg2_shared_set_rate_and_parent(struct clk_hw *hw,
+		unsigned long rate, unsigned long parent_rate, u8 index)
+{
+	return clk_rcg2_shared_set_rate(hw, rate, parent_rate);
+}
+
+static int clk_rcg2_shared_enable(struct clk_hw *hw)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+	int ret;
+
+	/*
+	 * Set the update bit because required configuration has already
+	 * been written in clk_rcg2_shared_set_rate()
+	 */
+	ret = clk_rcg2_set_force_enable(hw);
+	if (ret)
+		return ret;
+
+	ret = update_config(rcg);
+	if (ret)
+		return ret;
+
+	return clk_rcg2_clear_force_enable(hw);
+}
+
+static void clk_rcg2_shared_disable(struct clk_hw *hw)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+	u32 cfg;
+
+	/*
+	 * Store current configuration as switching to safe source would clear
+	 * the SRC and DIV of CFG register
+	 */
+	regmap_read(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, &cfg);
+
+	/*
+	 * Park the RCG at a safe configuration - sourced off of safe source.
+	 * Force enable and disable the RCG while configuring it to safeguard
+	 * against any update signal coming from the downstream clock.
+	 * The current parent is still prepared and enabled at this point, and
+	 * the safe source is always on while application processor subsystem
+	 * is online. Therefore, the RCG can safely switch its parent.
+	 */
+	clk_rcg2_set_force_enable(hw);
+
+	regmap_write(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG,
+		     rcg->safe_src_index << CFG_SRC_SEL_SHIFT);
+
+	update_config(rcg);
+
+	clk_rcg2_clear_force_enable(hw);
+
+	/* Write back the stored configuration corresponding to current rate */
+	regmap_write(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, cfg);
+}
+
+const struct clk_ops clk_rcg2_shared_ops = {
+	.enable = clk_rcg2_shared_enable,
+	.disable = clk_rcg2_shared_disable,
+	.get_parent = clk_rcg2_get_parent,
+	.set_parent = clk_rcg2_set_parent,
+	.recalc_rate = clk_rcg2_recalc_rate,
+	.determine_rate = clk_rcg2_determine_rate,
+	.set_rate = clk_rcg2_shared_set_rate,
+	.set_rate_and_parent = clk_rcg2_shared_set_rate_and_parent,
+};
+EXPORT_SYMBOL_GPL(clk_rcg2_shared_ops);