i2c: designware: Do not require clock when SSCN and FFCN are provided

The current driver uses input clock source frequency to calculate
values for [SS|FS]_[HC|LC] registers. However, when booting ACPI, we do not
currently have a good way to provide the frequency information.
Instead, we can leverage the SSCN and FFCN ACPI methods, which can be used
to directly provide these values. So, the clock information should
no longer be required during probing.

However, since clk can be invalid, additional checks must be done where
we are making use of it.

Signed-off-by: Mika Westerberg <[e-mail]>
Signed-off-by: Suravee Suthikulpanit <[e-mail]>
Tested-by: Loc Ho <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/i2c-designware-core.c

···
 		 enable ? "en" : "dis");
 }
 
+static unsigned long i2c_dw_clk_rate(struct dw_i2c_dev *dev)
+{
+	/*
+	 * Clock is not necessary if we got LCNT/HCNT values directly from
+	 * the platform code.
+	 */
+	if (WARN_ON_ONCE(!dev->get_clk_rate_khz))
+		return 0;
+	return dev->get_clk_rate_khz(dev);
+}
+
 /**
  * i2c_dw_init() - initialize the designware i2c master hardware
  * @dev: device private data
···
  */
 int i2c_dw_init(struct dw_i2c_dev *dev)
 {
-	u32 input_clock_khz;
 	u32 hcnt, lcnt;
 	u32 reg;
 	u32 sda_falling_time, scl_falling_time;
···
 			return ret;
 		}
 	}
-
-	input_clock_khz = dev->get_clk_rate_khz(dev);
 
 	reg = dw_readl(dev, DW_IC_COMP_TYPE);
 	if (reg == ___constant_swab32(DW_IC_COMP_TYPE_VALUE)) {
···
 		hcnt = dev->ss_hcnt;
 		lcnt = dev->ss_lcnt;
 	} else {
-		hcnt = i2c_dw_scl_hcnt(input_clock_khz,
+		hcnt = i2c_dw_scl_hcnt(i2c_dw_clk_rate(dev),
 					4000,	/* tHD;STA = tHIGH = 4.0 us */
 					sda_falling_time,
 					0,	/* 0: DW default, 1: Ideal */
 					0);	/* No offset */
-		lcnt = i2c_dw_scl_lcnt(input_clock_khz,
+		lcnt = i2c_dw_scl_lcnt(i2c_dw_clk_rate(dev),
 					4700,	/* tLOW = 4.7 us */
 					scl_falling_time,
 					0);	/* No offset */
···
 		hcnt = dev->fs_hcnt;
 		lcnt = dev->fs_lcnt;
 	} else {
-		hcnt = i2c_dw_scl_hcnt(input_clock_khz,
+		hcnt = i2c_dw_scl_hcnt(i2c_dw_clk_rate(dev),
 					600,	/* tHD;STA = tHIGH = 0.6 us */
 					sda_falling_time,
 					0,	/* 0: DW default, 1: Ideal */
 					0);	/* No offset */
-		lcnt = i2c_dw_scl_lcnt(input_clock_khz,
+		lcnt = i2c_dw_scl_lcnt(i2c_dw_clk_rate(dev),
 					1300,	/* tLOW = 1.3 us */
 					scl_falling_time,
 					0);	/* No offset */

drivers/i2c/busses/i2c-designware-platdrv.c

···
 }
 #endif
 
+static int i2c_dw_plat_prepare_clk(struct dw_i2c_dev *i_dev, bool prepare)
+{
+	if (IS_ERR(i_dev->clk))
+		return PTR_ERR(i_dev->clk);
+
+	if (prepare)
+		return clk_prepare_enable(i_dev->clk);
+
+	clk_disable_unprepare(i_dev->clk);
+	return 0;
+}
+
 static int dw_i2c_plat_probe(struct platform_device *pdev)
 {
 	struct dw_i2c_dev *dev;
···
 			DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_FAST;
 
 	dev->clk = devm_clk_get(&pdev->dev, NULL);
-	dev->get_clk_rate_khz = i2c_dw_get_clk_rate_khz;
-	if (IS_ERR(dev->clk))
-		return PTR_ERR(dev->clk);
-	clk_prepare_enable(dev->clk);
+	if (!i2c_dw_plat_prepare_clk(dev, true)) {
+		dev->get_clk_rate_khz = i2c_dw_get_clk_rate_khz;
 
-	if (!dev->sda_hold_time && ht) {
-		u32 ic_clk = dev->get_clk_rate_khz(dev);
-
-		dev->sda_hold_time = div_u64((u64)ic_clk * ht + 500000,
-					     1000000);
+		if (!dev->sda_hold_time && ht)
+			dev->sda_hold_time = div_u64(
+				(u64)dev->get_clk_rate_khz(dev) * ht + 500000,
+				1000000);
 	}
 
 	if (!dev->tx_fifo_depth) {
···
 	struct dw_i2c_dev *i_dev = platform_get_drvdata(pdev);
 
 	i2c_dw_disable(i_dev);
-	clk_disable_unprepare(i_dev->clk);
+	i2c_dw_plat_prepare_clk(i_dev, false);
 
 	return 0;
 }
···
 	struct platform_device *pdev = to_platform_device(dev);
 	struct dw_i2c_dev *i_dev = platform_get_drvdata(pdev);
 
-	clk_prepare_enable(i_dev->clk);
+	i2c_dw_plat_prepare_clk(i_dev, true);
 
 	if (!i_dev->pm_runtime_disabled)
 		i2c_dw_init(i_dev);