clk: fsl-sai: new driver

With this driver it is possible to use the BCLK pin of the SAI module as
a generic clock output. This is esp. useful if you want to drive a clock
to an audio codec. Because the output only allows integer divider values
the audio codec needs an integrated PLL.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lkml.kernel.org/r/20200102231101.11834-3-michael@walle.cc
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/Kconfig

@@ -174,6 +174,18 @@ config COMMON_CLK_CS2000_CP
 	help
 	  If you say yes here you get support for the CS2000 clock multiplier.
 
+config COMMON_CLK_FSL_SAI
+	bool "Clock driver for BCLK of Freescale SAI cores"
+	depends on ARCH_LAYERSCAPE || COMPILE_TEST
+	help
+	  This driver supports the Freescale SAI (Synchronous Audio Interface)
+	  to be used as a generic clock output. Some SoCs have restrictions
+	  regarding the possible pin multiplexer settings. Eg. on some SoCs
+	  two SAI interfaces can only be enabled together. If just one is
+	  needed, the BCLK pin of the second one can be used as general
+	  purpose clock output. Ideally, it can be used to drive an audio
+	  codec (sometimes known as MCLK).
+
 config COMMON_CLK_GEMINI
 	bool "Clock driver for Cortina Systems Gemini SoC"
 	depends on ARCH_GEMINI || COMPILE_TEST

drivers/clk/Makefile

@@ -29,6 +29,7 @@ obj-$(CONFIG_ARCH_CLPS711X)		+= clk-clps711x.o
 obj-$(CONFIG_COMMON_CLK_CS2000_CP)	+= clk-cs2000-cp.o
 obj-$(CONFIG_ARCH_EFM32)		+= clk-efm32gg.o
 obj-$(CONFIG_COMMON_CLK_FIXED_MMIO)	+= clk-fixed-mmio.o
+obj-$(CONFIG_COMMON_CLK_FSL_SAI)	+= clk-fsl-sai.o
 obj-$(CONFIG_COMMON_CLK_GEMINI)		+= clk-gemini.o
 obj-$(CONFIG_COMMON_CLK_ASPEED)		+= clk-aspeed.o
 obj-$(CONFIG_MACH_ASPEED_G6)		+= clk-ast2600.o

drivers/clk/clk-fsl-sai.c

@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Freescale SAI BCLK as a generic clock driver
+ *
+ * Copyright 2020 Michael Walle <michael@walle.cc>
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/clk-provider.h>
+#include <linux/err.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/slab.h>
+
+#define I2S_CSR		0x00
+#define I2S_CR2		0x08
+#define CSR_BCE_BIT	28
+#define CR2_BCD		BIT(24)
+#define CR2_DIV_SHIFT	0
+#define CR2_DIV_WIDTH	8
+
+struct fsl_sai_clk {
+	struct clk_divider div;
+	struct clk_gate gate;
+	spinlock_t lock;
+};
+
+static int fsl_sai_clk_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct fsl_sai_clk *sai_clk;
+	struct clk_parent_data pdata = { .index = 0 };
+	void __iomem *base;
+	struct clk_hw *hw;
+	struct resource *res;
+
+	sai_clk = devm_kzalloc(dev, sizeof(*sai_clk), GFP_KERNEL);
+	if (!sai_clk)
+		return -ENOMEM;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	base = devm_ioremap_resource(dev, res);
+	if (IS_ERR(base))
+		return PTR_ERR(base);
+
+	spin_lock_init(&sai_clk->lock);
+
+	sai_clk->gate.reg = base + I2S_CSR;
+	sai_clk->gate.bit_idx = CSR_BCE_BIT;
+	sai_clk->gate.lock = &sai_clk->lock;
+
+	sai_clk->div.reg = base + I2S_CR2;
+	sai_clk->div.shift = CR2_DIV_SHIFT;
+	sai_clk->div.width = CR2_DIV_WIDTH;
+	sai_clk->div.lock = &sai_clk->lock;
+
+	/* set clock direction, we are the BCLK master */
+	writel(CR2_BCD, base + I2S_CR2);
+
+	hw = clk_hw_register_composite_pdata(dev, dev->of_node->name,
+					     &pdata, 1, NULL, NULL,
+					     &sai_clk->div.hw,
+					     &clk_divider_ops,
+					     &sai_clk->gate.hw,
+					     &clk_gate_ops,
+					     CLK_SET_RATE_GATE);
+	if (IS_ERR(hw))
+		return PTR_ERR(hw);
+
+	return devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get, hw);
+}
+
+static const struct of_device_id of_fsl_sai_clk_ids[] = {
+	{ .compatible = "fsl,vf610-sai-clock" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, of_fsl_sai_clk_ids);
+
+static struct platform_driver fsl_sai_clk_driver = {
+	.probe = fsl_sai_clk_probe,
+	.driver		= {
+		.name	= "fsl-sai-clk",
+		.of_match_table = of_fsl_sai_clk_ids,
+	},
+};
+module_platform_driver(fsl_sai_clk_driver);
+
+MODULE_DESCRIPTION("Freescale SAI bitclock-as-a-clock driver");
+MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:fsl-sai-clk");