[PATCH v6 1/6] clk: bcm: rpi: Manage clock rate in prepare/unprepare callbacks

[Maíra Canal]

On current firmware versions, RPI_FIRMWARE_SET_CLOCK_STATE doesn't
actually power off the clock. To achieve meaningful power savings, the
clock rate must be set to the minimum before disabling. This might be
fixed in future firmware releases.

Rather than pushing rate management to clock consumers, handle it
directly in the clock framework's prepare/unprepare callbacks. In
unprepare, set the rate to the firmware-reported minimum before
disabling the clock. In prepare, for clocks marked with `maximize`
(currently v3d), restore the rate to the maximum after enabling.

Signed-off-by: Maíra Canal <mcanal at igalia.com>
---
 drivers/clk/bcm/clk-raspberrypi.c | 61 ++++++++++++++++++++++-----------------
 1 file changed, 35 insertions(+), 26 deletions(-)

diff --git a/drivers/clk/bcm/clk-raspberrypi.c b/drivers/clk/bcm/clk-raspberrypi.c
index 1a9162f0ae31e330c46f6eafdd00350599b0eede..0d6e4f43c3bac0e7b38934c5c6e4db51211233de 100644
--- a/drivers/clk/bcm/clk-raspberrypi.c
+++ b/drivers/clk/bcm/clk-raspberrypi.c
@@ -66,7 +66,8 @@ const struct raspberrypi_clk_data *clk_hw_to_data(const struct clk_hw *hw)
 struct raspberrypi_clk_variant {
 	bool		export;
 	char		*clkdev;
-	unsigned long	min_rate;
+	u32		min_rate;
+	u32		max_rate;
 	bool		minimize;
 	bool		maximize;
 	u32		flags;
@@ -289,16 +290,22 @@ static int raspberrypi_fw_dumb_determine_rate(struct clk_hw *hw,
 static int raspberrypi_fw_prepare(struct clk_hw *hw)
 {
 	const struct raspberrypi_clk_data *data = clk_hw_to_data(hw);
+	struct raspberrypi_clk_variant *variant = data->variant;
 	struct raspberrypi_clk *rpi = data->rpi;
 	u32 state = RPI_FIRMWARE_STATE_ENABLE_BIT;
 	int ret;
 
 	ret = raspberrypi_clock_property(rpi->firmware, data,
 					 RPI_FIRMWARE_SET_CLOCK_STATE, &state);
-	if (ret)
+	if (ret) {
 		dev_err_ratelimited(rpi->dev,
 				    "Failed to set clock %s state to on: %d\n",
 				    clk_hw_get_name(hw), ret);
+		return ret;
+	}
+
+	if (variant->maximize)
+		ret = raspberrypi_fw_set_rate(hw, variant->max_rate, 0);
 
 	return ret;
 }
@@ -306,10 +313,19 @@ static int raspberrypi_fw_prepare(struct clk_hw *hw)
 static void raspberrypi_fw_unprepare(struct clk_hw *hw)
 {
 	const struct raspberrypi_clk_data *data = clk_hw_to_data(hw);
+	struct raspberrypi_clk_variant *variant = data->variant;
 	struct raspberrypi_clk *rpi = data->rpi;
 	u32 state = 0;
 	int ret;
 
+	/*
+	 * On current firmware versions, RPI_FIRMWARE_SET_CLOCK_STATE doesn't
+	 * actually power off the clock. To achieve meaningful power consumption
+	 * reduction, the driver needs to set the clock rate to minimum before
+	 * disabling it.
+	 */
+	raspberrypi_fw_set_rate(hw, variant->min_rate, 0);
+
 	ret = raspberrypi_clock_property(rpi->firmware, data,
 					 RPI_FIRMWARE_SET_CLOCK_STATE, &state);
 	if (ret)
@@ -334,7 +350,7 @@ static struct clk_hw *raspberrypi_clk_register(struct raspberrypi_clk *rpi,
 {
 	struct raspberrypi_clk_data *data;
 	struct clk_init_data init = {};
-	u32 min_rate, max_rate;
+	unsigned long rate;
 	int ret;
 
 	data = devm_kzalloc(rpi->dev, sizeof(*data), GFP_KERNEL);
@@ -354,18 +370,20 @@ static struct clk_hw *raspberrypi_clk_register(struct raspberrypi_clk *rpi,
 
 	data->hw.init = &init;
 
-	ret = raspberrypi_clock_property(rpi->firmware, data,
-					 RPI_FIRMWARE_GET_MIN_CLOCK_RATE,
-					 &min_rate);
-	if (ret) {
-		dev_err(rpi->dev, "Failed to get clock %d min freq: %d\n",
-			id, ret);
-		return ERR_PTR(ret);
+	if (!variant->min_rate) {
+		ret = raspberrypi_clock_property(rpi->firmware, data,
+						 RPI_FIRMWARE_GET_MIN_CLOCK_RATE,
+						 &variant->min_rate);
+		if (ret) {
+			dev_err(rpi->dev, "Failed to get clock %d min freq: %d\n",
+				id, ret);
+			return ERR_PTR(ret);
+		}
 	}
 
 	ret = raspberrypi_clock_property(rpi->firmware, data,
 					 RPI_FIRMWARE_GET_MAX_CLOCK_RATE,
-					 &max_rate);
+					 &variant->max_rate);
 	if (ret) {
 		dev_err(rpi->dev, "Failed to get clock %d max freq: %d\n",
 			id, ret);
@@ -376,7 +394,7 @@ static struct clk_hw *raspberrypi_clk_register(struct raspberrypi_clk *rpi,
 	if (ret)
 		return ERR_PTR(ret);
 
-	clk_hw_set_rate_range(&data->hw, min_rate, max_rate);
+	clk_hw_set_rate_range(&data->hw, variant->min_rate, variant->max_rate);
 
 	if (variant->clkdev) {
 		ret = devm_clk_hw_register_clkdev(rpi->dev, &data->hw,
@@ -387,20 +405,11 @@ static struct clk_hw *raspberrypi_clk_register(struct raspberrypi_clk *rpi,
 		}
 	}
 
-	if (variant->maximize)
-		variant->min_rate = max_rate;
-
-	if (variant->min_rate) {
-		unsigned long rate;
-
-		clk_hw_set_rate_range(&data->hw, variant->min_rate, max_rate);
-
-		rate = raspberrypi_fw_get_rate(&data->hw, 0);
-		if (rate < variant->min_rate) {
-			ret = raspberrypi_fw_set_rate(&data->hw, variant->min_rate, 0);
-			if (ret)
-				return ERR_PTR(ret);
-		}
+	rate = raspberrypi_fw_get_rate(&data->hw, 0);
+	if (rate < variant->min_rate) {
+		ret = raspberrypi_fw_set_rate(&data->hw, variant->min_rate, 0);
+		if (ret)
+			return ERR_PTR(ret);
 	}
 
 	return &data->hw;

-- 
2.52.0