clk: bcm: rpi: Discover the firmware clocks

The RaspberryPi4 firmware actually exposes more clocks than are currently
handled by the driver and we will need to change some of them directly
based on the pixel rate for the display related clocks, or the load for the
GPU.

Since the firmware implements DVFS, this rate change can have a number of
side-effects, including adjusting the various PLL voltages or the PLL
parents. The firmware also implements thermal throttling, so even some
thermal pressure can change those parameters behind Linux back.

DVFS is currently implemented on the arm, core, h264, v3d, isp and hevc
clocks, so updating any of them using the MMIO driver (and thus behind the
firmware's back) can lead to troubles, the arm clock obviously being the
most problematic.

In order to make Linux play as nice as possible with those constraints, it
makes sense to rely on the firmware clocks as much as possible. However,
the firmware doesn't seem to provide some equivalents to their MMIO
counterparts, so we can't really replace that driver entirely.

Fortunately, the firmware has an interface to discover the clocks it
exposes.

Let's use it to discover, register the clocks in the clocks framework and
then expose them through the device tree for consumers to use them.

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: linux-clk@vger.kernel.org
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/438d73962741a8c5f7c689319b7443b930a87fde.1592210452.git-series.maxime@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/bcm/clk-raspberrypi.c

@@ -296,14 +296,151 @@ static struct clk_hw *raspberrypi_register_pllb_arm(struct raspberrypi_clk *rpi)
 	return &raspberrypi_clk_pllb_arm.hw;
 }
 
+static int raspberrypi_fw_dumb_determine_rate(struct clk_hw *hw,
+					      struct clk_rate_request *req)
+{
+	/*
+	 * The firmware will do the rounding but that isn't part of
+	 * the interface with the firmware, so we just do our best
+	 * here.
+	 */
+	req->rate = clamp(req->rate, req->min_rate, req->max_rate);
+	return 0;
+}
+
+static const struct clk_ops raspberrypi_firmware_clk_ops = {
+	.is_prepared	= raspberrypi_fw_is_prepared,
+	.recalc_rate	= raspberrypi_fw_get_rate,
+	.determine_rate	= raspberrypi_fw_dumb_determine_rate,
+	.set_rate	= raspberrypi_fw_set_rate,
+};
+
+static struct clk_hw *raspberrypi_clk_register(struct raspberrypi_clk *rpi,
+					       unsigned int parent,
+					       unsigned int id)
+{
+	struct raspberrypi_clk_data *data;
+	struct clk_init_data init = {};
+	u32 min_rate, max_rate;
+	int ret;
+
+	if (id == RPI_FIRMWARE_ARM_CLK_ID) {
+		struct clk_hw *hw;
+
+		hw = raspberrypi_register_pllb(rpi);
+		if (IS_ERR(hw)) {
+			dev_err(rpi->dev, "Failed to initialize pllb, %ld\n",
+				PTR_ERR(hw));
+			return hw;
+		}
+
+		return raspberrypi_register_pllb_arm(rpi);
+	}
+
+	data = devm_kzalloc(rpi->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return ERR_PTR(-ENOMEM);
+	data->rpi = rpi;
+	data->id = id;
+
+	init.name = devm_kasprintf(rpi->dev, GFP_KERNEL, "fw-clk-%u", id);
+	init.ops = &raspberrypi_firmware_clk_ops;
+	init.flags = CLK_GET_RATE_NOCACHE;
+
+	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",
+			id, ret);
+		return ERR_PTR(ret);
+	}
+
+	ret = raspberrypi_clock_property(rpi->firmware, data,
+					 RPI_FIRMWARE_GET_MAX_CLOCK_RATE,
+					 &max_rate);
+	if (ret) {
+		dev_err(rpi->dev, "Failed to get clock %d max freq: %d\n",
+			id, ret);
+		return ERR_PTR(ret);
+	}
+
+	ret = devm_clk_hw_register(rpi->dev, &data->hw);
+	if (ret)
+		return ERR_PTR(ret);
+
+	clk_hw_set_rate_range(&data->hw, min_rate, max_rate);
+
+	if (id == RPI_FIRMWARE_ARM_CLK_ID) {
+		ret = devm_clk_hw_register_clkdev(rpi->dev, &data->hw,
+						  NULL, "cpu0");
+		if (ret) {
+			dev_err(rpi->dev, "Failed to initialize clkdev\n");
+			return ERR_PTR(ret);
+		}
+	}
+
+	return &data->hw;
+}
+
+struct rpi_firmware_get_clocks_response {
+	u32 parent;
+	u32 id;
+};
+
+static int raspberrypi_discover_clocks(struct raspberrypi_clk *rpi,
+				       struct clk_hw_onecell_data *data)
+{
+	struct rpi_firmware_get_clocks_response *clks;
+	int ret;
+
+	clks = devm_kcalloc(rpi->dev,
+			    sizeof(*clks), RPI_FIRMWARE_NUM_CLK_ID,
+			    GFP_KERNEL);
+	if (!clks)
+		return -ENOMEM;
+
+	ret = rpi_firmware_property(rpi->firmware, RPI_FIRMWARE_GET_CLOCKS,
+				    clks,
+				    sizeof(*clks) * RPI_FIRMWARE_NUM_CLK_ID);
+	if (ret)
+		return ret;
+
+	while (clks->id) {
+		struct clk_hw *hw;
+
+		switch (clks->id) {
+		case RPI_FIRMWARE_ARM_CLK_ID:
+		case RPI_FIRMWARE_CORE_CLK_ID:
+		case RPI_FIRMWARE_M2MC_CLK_ID:
+		case RPI_FIRMWARE_V3D_CLK_ID:
+			hw = raspberrypi_clk_register(rpi, clks->parent,
+						      clks->id);
+			if (IS_ERR(hw))
+				return PTR_ERR(hw);
+
+			data->hws[clks->id] = hw;
+			data->num = clks->id + 1;
+			fallthrough;
+
+		default:
+			clks++;
+			break;
+		}
+	}
+
+	return 0;
+}
+
 static int raspberrypi_clk_probe(struct platform_device *pdev)
 {
 	struct clk_hw_onecell_data *clk_data;
 	struct device_node *firmware_node;
 	struct device *dev = &pdev->dev;
 	struct rpi_firmware *firmware;
 	struct raspberrypi_clk *rpi;
-	struct clk_hw *hw;
 	int ret;
 
 	/*
@@ -340,17 +477,9 @@ static int raspberrypi_clk_probe(struct platform_device *pdev)
 	if (!clk_data)
 		return -ENOMEM;
 
-	hw = raspberrypi_register_pllb(rpi);
-	if (IS_ERR(hw)) {
-		dev_err(dev, "Failed to initialize pllb, %ld\n", PTR_ERR(hw));
-		return PTR_ERR(hw);
-	}
-
-	hw = raspberrypi_register_pllb_arm(rpi);
-	if (IS_ERR(hw))
-		return PTR_ERR(hw);
-	clk_data->hws[RPI_FIRMWARE_ARM_CLK_ID] = hw;
-	clk_data->num = RPI_FIRMWARE_ARM_CLK_ID + 1;
+	ret = raspberrypi_discover_clocks(rpi, clk_data);
+	if (ret)
+		return ret;
 
 	ret = devm_of_clk_add_hw_provider(dev, of_clk_hw_onecell_get,
 					  clk_data);