[RFC PATCH 1/2] clk: qcom: implement RCG2 'parked' clock support

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

clk_rcg2_shared_ops implements support for the case of the RCG which
must not be completely turned off. However its design has one major
drawback: it doesn't allow us to properly implement the is_enabled
callback, which causes different kinds of misbehaviour from the CCF.

Follow the idea behind clk_regmap_phy_mux_ops and implement the new
clk_rcg2_parked_ops. It also targets the clocks which must not be fully
switched off (and shared most of the implementation with
clk_rcg2_shared_ops). The major difference is that it requires that the
parent map doesn't conain the safe (parked) clock source. Instead if the
CFG_REG register points to the safe source, the clock is considered to
be disabled.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
 drivers/clk/qcom/clk-rcg.h  |  1 +
 drivers/clk/qcom/clk-rcg2.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/drivers/clk/qcom/clk-rcg.h b/drivers/clk/qcom/clk-rcg.h
index e6d84c8c7989..9fbbf1251564 100644
--- a/drivers/clk/qcom/clk-rcg.h
+++ b/drivers/clk/qcom/clk-rcg.h
@@ -176,6 +176,7 @@ 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;
+extern const struct clk_ops clk_rcg2_parked_ops;
 extern const struct clk_ops clk_dp_ops;
 
 struct clk_rcg_dfs_data {
diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
index 5183c74b074f..3f52abf0025e 100644
--- a/drivers/clk/qcom/clk-rcg2.c
+++ b/drivers/clk/qcom/clk-rcg2.c
@@ -5,6 +5,7 @@
 
 #include <linux/kernel.h>
 #include <linux/bitops.h>
+#include <linux/bitfield.h>
 #include <linux/err.h>
 #include <linux/bug.h>
 #include <linux/export.h>
@@ -1150,6 +1151,39 @@ const struct clk_ops clk_rcg2_shared_ops = {
 };
 EXPORT_SYMBOL_GPL(clk_rcg2_shared_ops);
 
+static int clk_rcg2_park_is_enabled(struct clk_hw *hw)
+{
+	struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+	u32 cfg;
+	int ret;
+
+	if (!clk_rcg2_is_enabled(hw))
+		return false;
+
+	ret = regmap_read(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, &cfg);
+	if (ret)
+		return ret;
+
+	return FIELD_GET(CFG_SRC_SEL_MASK, cfg) != rcg->safe_src_index;
+}
+
+/*
+ * Unlike clk_rcg2_shared_ops, the safe_src_index aka XO must NOT be present in
+ * parent_map. This allows us to implement proper is_enabled callback.
+ */
+const struct clk_ops clk_rcg2_parked_ops = {
+	.is_enabled = clk_rcg2_park_is_enabled,
+	.enable = clk_rcg2_shared_enable,
+	.disable = clk_rcg2_shared_disable,
+	.get_parent = clk_rcg2_shared_get_parent,
+	.set_parent = clk_rcg2_shared_set_parent,
+	.recalc_rate = clk_rcg2_shared_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_parked_ops);
+
 /* Common APIs to be used for DFS based RCGR */
 static void clk_rcg2_dfs_populate_freq(struct clk_hw *hw, unsigned int l,
 				       struct freq_tbl *f)
-- 
2.39.2