Hi Dillon
On 5/14/21 1:02 PM, dillon.minfei@xxxxxxxxx wrote:
> From: Dillon Min <dillon.minfei@xxxxxxxxx>
>
> 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@xxxxxxxxx/
> Signed-off-by: Dillon Min <dillon.minfei@xxxxxxxxx>
> ---
> 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
>
I tested this patch on STM32F429-Disco, it fixes the issue described by Dillon.
But i think it's not a good idea to make usage of #if !defined(CONFIG_MMU) && !defined(CONFIG_XIP_KERNEL)
inside the driver code.
Pierre-Yves, Alain, as i am not I2C expert, can you have a look at this patch and propose another solution
to fix the original issue described by Dillon ?
Thanks
Patrice
