linux-kernel - [PATCH] i2c: designware: Do not require clock when SSCN and FFCN are provided

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Date:	Tue, 15 Dec 2015 16:38:58 -0600
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	<mika.westerberg@...ux.intel.com>, <wsa@...-dreams.de>
CC:	<lho@....com>, <Ken.Xue@....com>, <linux-i2c@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"Suravee Suthikulpanit" <Suravee.Suthikulpanit@....com>
Subject: [PATCH] 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, this patch removes the clock requirement when SSCN and FFCN
are provided.

Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
---

Note: This has been tested on AMD Seattle RevB for both DT and ACPI.

 drivers/i2c/busses/i2c-designware-core.c    |  5 +++--
 drivers/i2c/busses/i2c-designware-platdrv.c | 30 +++++++++++++++++++++++------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 8c48b27..ec458ec 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -281,7 +281,7 @@ static void __i2c_dw_enable(struct dw_i2c_dev *dev, bool enable)
  */
 int i2c_dw_init(struct dw_i2c_dev *dev)
 {
-	u32 input_clock_khz;
+	u32 input_clock_khz = 0;
 	u32 hcnt, lcnt;
 	u32 reg;
 	u32 sda_falling_time, scl_falling_time;
@@ -295,7 +295,8 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
 		}
 	}
 
-	input_clock_khz = dev->get_clk_rate_khz(dev);
+	if (dev->get_clk_rate_khz)
+		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)) {
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index 809579e..57f623b 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -127,6 +127,26 @@ static inline int dw_i2c_acpi_configure(struct platform_device *pdev)
 }
 #endif
 
+static int dw_i2c_configure_clk(struct platform_device *pdev,
+				struct dw_i2c_dev *dev)
+{
+	/* For ACPI, if SSCN and FMCN is provided, we should not
+	 * need the clock value.
+	 */
+	if (has_acpi_companion(&pdev->dev) &&
+	    dev->ss_hcnt && dev->ss_lcnt &&
+	    dev->fs_hcnt && dev->fs_lcnt)
+		return 0;
+
+	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);
+
+	return 0;
+}
+
 static int dw_i2c_plat_probe(struct platform_device *pdev)
 {
 	struct dw_i2c_dev *dev;
@@ -203,13 +223,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
 		dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
 			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);
+	r = dw_i2c_configure_clk(pdev, dev);
+	if (r)
+		return r;
 
-	if (!dev->sda_hold_time && ht) {
+	if (!dev->sda_hold_time && ht && dev->get_clk_rate_khz) {
 		u32 ic_clk = dev->get_clk_rate_khz(dev);
 
 		dev->sda_hold_time = div_u64((u64)ic_clk * ht + 500000,
-- 
2.5.0

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