On 27/11/2021 23:32, Sam Protsenko wrote:

USIv2 IP-core is found on modern ARM64 Exynos SoCs (like Exynos850) and
provides selectable serial protocol (one of: UART, SPI, I2C). USIv2
registers usually reside in the same register map as a particular
underlying protocol it implements, but have some particular offset. E.g.
on Exynos850 the USI_UART has 0x13820000 base address, where UART
registers have 0x00..0x40 offsets, and USI registers have 0xc0..0xdc
offsets. Desired protocol can be chosen via SW_CONF register from System
Register block of the same domain as USI.

Before starting to use a particular protocol, USIv2 must be configured
properly:
  1. Select protocol to be used via System Register
  2. Clear "reset" flag in USI_CON
  3. Configure HWACG behavior (e.g. for UART Rx the HWACG must be
     disabled, so that the IP clock is not gated automatically); this is
     done using USI_OPTION register
  4. Keep both USI clocks (PCLK and IPCLK) running during USI registers
     modification

This driver implements above behavior. Of course, USIv2 driver should be
probed before UART/I2C/SPI drivers. It can be achived by embedding
UART/I2C/SPI nodes inside of USI node (in Device Tree); driver then
walks underlying nodes and instantiates those. Driver also handles USI
configuration on PM resume, as register contents can be lost during CPU
suspend.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
---
 drivers/soc/samsung/Kconfig         |  14 ++
 drivers/soc/samsung/Makefile        |   2 +
 drivers/soc/samsung/exynos-usi-v2.c | 242 ++++++++++++++++++++++++++++

You used everywhere v2 naming, but I actually hope this driver will be
able to support also v1 and vx of USI. IOW, I expect to have only one
USI driver, so please drop everywhere v2 (bindings, symbols, Kconfig,
functions) except the compatible.

Everywhere here:
s/usi_v2/exynos_usi/

+	const char *name;		/* mode name */
+	unsigned int val;		/* mode register value */
+};
+
+struct usi_v2 {
+	struct device *dev;> +	void __iomem *regs;		/* USI register map */
+	struct clk *pclk;		/* USI bus clock */
+	struct clk *ipclk;		/* USI operating clock */
+
+	size_t mode;			/* current USI SW_CONF mode index */
+	bool clkreq_on;			/* always provide clock to IP */
+
+	/* System Register */
+	struct regmap *sysreg;		/* System Register map */
+	unsigned int sw_conf;		/* SW_CONF register offset in sysreg */
+};
+
+static const struct usi_v2_mode usi_v2_modes[] = {
+	[USI_V2_UART] =	{ .name = "uart", .val = SW_CONF_UART },
+	[USI_V2_SPI] =	{ .name = "spi",  .val = SW_CONF_SPI },
+	[USI_V2_I2C] =	{ .name = "i2c",  .val = SW_CONF_I2C },
+};
+
+/**
+ * usi_v2_set_sw_conf - Set USI block configuration mode
+ * @usi: USI driver object
+ * @mode: Mode index
+ *
+ * Select underlying serial protocol (UART/SPI/I2C) in USI IP-core.
+ *
+ * Return: 0 on success, or negative error code on failure.
+ */
+static int usi_v2_set_sw_conf(struct usi_v2 *usi, size_t mode)
+{
+	unsigned int val;
+	int ret;
+
+	if (mode >= ARRAY_SIZE(usi_v2_modes))
+		return -EINVAL;
+
+	val = usi_v2_modes[mode].val;
+	ret = regmap_update_bits(usi->sysreg, usi->sw_conf, SW_CONF_MASK, val);
+	if (ret)
+		return ret;
+
+	usi->mode = mode;
+	dev_dbg(usi->dev, "USIv2 protocol: %s\n", usi_v2_modes[usi->mode].name);
+
+	return 0;
+}
+
+/**
+ * usi_v2_enable - Initialize USI block
+ * @usi: USI driver object
+ *
+ * USI IP-core start state is "reset" (on startup and after CPU resume). This
+ * routine enables USI block by clearing the reset flag. It also configures
+ * HWACG behavior (needed e.g. for UART Rx). It should be performed before
+ * underlying protocol becomes functional.
+ *
+ * Both 'pclk' and 'ipclk' clocks should be enabled when running this function.
+ */
+static void usi_v2_enable(const struct usi_v2 *usi)
+{
+	u32 val;
+
+	/* Enable USI block */
+	val = readl(usi->regs + USI_CON);
+	val &= ~USI_CON_RESET;
+	writel(val, usi->regs + USI_CON);
+	udelay(1);
+
+	/* Continuously provide the clock to USI IP w/o gating */
+	if (usi->clkreq_on) {
+		val = readl(usi->regs + USI_OPTION);
+		val &= ~USI_OPTION_CLKSTOP_ON;
+		val |= USI_OPTION_CLKREQ_ON;
+		writel(val, usi->regs + USI_OPTION);
+	}
+}
+
+static int usi_v2_configure(struct usi_v2 *usi)
+{
+	int ret;
+
+	ret = clk_prepare_enable(usi->pclk);
+	if (ret)
+		return ret;
+
+	ret = clk_prepare_enable(usi->ipclk);
+	if (ret)
+		goto err_pclk;
+
+	ret = usi_v2_set_sw_conf(usi, usi->mode);
+	if (ret)
+		goto err_ipclk;
+
+	usi_v2_enable(usi);
+
+err_ipclk:
+	clk_disable_unprepare(usi->ipclk);
+err_pclk:
+	clk_disable_unprepare(usi->pclk);
+	return ret;
+}
+
+static int usi_v2_parse_dt(struct device_node *np, struct usi_v2 *usi)
+{
+	int ret;
+	u32 mode;
+
+	ret = of_property_read_u32(np, "samsung,mode", &mode);
+	if (ret)
+		return ret;
+	usi->mode = mode;

Parse and validate mode here, instead of usi_v2_set_sw_conf(). We expect
DT to be correct, so if it is not, then there is no point to probe the
device.

Best regards,
Krzysztof