Re: [PATCH 2/4] i2c: stm32f4: Fix stmpe811 get xyz data timeout issue

From: Dillon Min <redacted>

As stm32f429's internal flash is 2Mbytes and compiled kernel
image bigger than 2Mbytes, so we have to load kernel image
to sdram on stm32f429-disco board which has 8Mbytes sdram space.

based on above context, as you knows kernel running on external
sdram is more slower than internal flash. besides, we need read 4
bytes to get touch screen xyz(x, y, pressure) coordinate data in
stmpe811 interrupt.

so, in stm32f4_i2c_handle_rx_done, as i2c read slower than running
in xip mode, have to adjust 'STOP/START bit set position' from last
two bytes to last one bytes. else, will get i2c timeout in reading
touch screen coordinate.

to not bring in side effect, introduce IIC_LAST_BYTE_POS to support xip
kernel or zImage.

Fixes: 62817fc8d282 ("i2c: stm32f4: add driver")
Link: https://lore.kernel.org/lkml/1591709203-12106-5-git-send-email-dillon.minfei@gmail.com/ (local)
Signed-off-by: Dillon Min <redacted>
---
 drivers/i2c/busses/i2c-stm32f4.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-stm32f4.c b/drivers/i2c/busses/i2c-stm32f4.c
index 4933fc8ce3fd..2e41231b9037 100644
--- a/drivers/i2c/busses/i2c-stm32f4.c
+++ b/drivers/i2c/busses/i2c-stm32f4.c

@@ -93,6 +93,12 @@
 #define STM32F4_I2C_MAX_FREQ		46U
 #define HZ_TO_MHZ			1000000
 
+#if !defined(CONFIG_MMU) && !defined(CONFIG_XIP_KERNEL)
+#define IIC_LAST_BYTE_POS 1
+#else
+#define IIC_LAST_BYTE_POS 2
+#endif
+
 /**
  * struct stm32f4_i2c_msg - client specific data
  * @addr: 8-bit slave addr, including r/w bit

@@ -439,7 +445,7 @@ static void stm32f4_i2c_handle_rx_done(struct stm32f4_i2c_dev *i2c_dev)
 	int i;
 
 	switch (msg->count) {
-	case 2:
+	case IIC_LAST_BYTE_POS:
 		/*
 		 * In order to correctly send the Stop or Repeated Start
 		 * condition on the I2C bus, the STOP/START bit has to be set

@@ -454,7 +460,7 @@ static void stm32f4_i2c_handle_rx_done(struct stm32f4_i2c_dev *i2c_dev)
 		else
 			stm32f4_i2c_set_bits(reg, STM32F4_I2C_CR1_START);
 
-		for (i = 2; i > 0; i--)
+		for (i = IIC_LAST_BYTE_POS; i > 0; i--)
 			stm32f4_i2c_read_msg(i2c_dev);
 
 		reg = i2c_dev->base + STM32F4_I2C_CR2;

@@ -463,7 +469,7 @@ static void stm32f4_i2c_handle_rx_done(struct stm32f4_i2c_dev *i2c_dev)
 
 		complete(&i2c_dev->complete);
 		break;
-	case 3:
+	case (IIC_LAST_BYTE_POS+1):
 		/*
 		 * In order to correctly generate the NACK pulse after the last
 		 * received data byte, we have to enable NACK before reading N-2