i2c: designware: Avoid aborted transfers with fast reacting I2C slaves

[cascardo/linux.git] / drivers / i2c / busses / i2c-designware-core.c

diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 1fe93c4..11e866d 100644 (file)
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -95,6 +95,9 @@
 #define DW_IC_STATUS_TFE               BIT(2)
 #define DW_IC_STATUS_MST_ACTIVITY      BIT(5)
 
+#define DW_IC_SDA_HOLD_RX_SHIFT                16
+#define DW_IC_SDA_HOLD_RX_MASK         GENMASK(23, DW_IC_SDA_HOLD_RX_SHIFT)
+
 #define DW_IC_ERR_TX_ABRT      0x1
 
 #define DW_IC_TAR_10BITADDR_MASTER BIT(12)
@@ -420,12 +423,20 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
        /* Configure SDA Hold Time if required */
        reg = dw_readl(dev, DW_IC_COMP_VERSION);
        if (reg >= DW_IC_SDA_HOLD_MIN_VERS) {
-               if (dev->sda_hold_time) {
-                       dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
-               } else {
+               if (!dev->sda_hold_time) {
                        /* Keep previous hold time setting if no one set it */
                        dev->sda_hold_time = dw_readl(dev, DW_IC_SDA_HOLD);
                }
+               /*
+                * Workaround for avoiding TX arbitration lost in case I2C
+                * slave pulls SDA down "too quickly" after falling egde of
+                * SCL by enabling non-zero SDA RX hold. Specification says it
+                * extends incoming SDA low to high transition while SCL is
+                * high but it apprears to help also above issue.
+                */
+               if (!(dev->sda_hold_time & DW_IC_SDA_HOLD_RX_MASK))
+                       dev->sda_hold_time |= 1 << DW_IC_SDA_HOLD_RX_SHIFT;
+               dw_writel(dev, dev->sda_hold_time, DW_IC_SDA_HOLD);
        } else {
                dev_warn(dev->dev,
                        "Hardware too old to adjust SDA hold time.\n");