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

[Dillon Min <dillon.minfei@gmail.com>]

Hi Patrice, Pierre-Yves, Alain

On Tue, Jun 1, 2021 at 7:43 PM Patrice CHOTARD
<patrice.chotard@foss.st.com> wrote:
>
> Hi Dillon
>
> On 5/14/21 1:02 PM, dillon.minfei@gmail.com wrote:
> > From: Dillon Min <dillon.minfei@gmail.com>
> >
> > 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/
> > Signed-off-by: Dillon Min <dillon.minfei@gmail.com>
> > ---
> >  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.

Hi Patrice,
Thanks for your time.

How about introducing a dts node for this purpose.
like
stm32-i2c,last-byte-pos = <1>;
or
stm32-i2c,last-byte-pos = <2>;

if not set, the default value is 2

Best Regards
Dillon

>
> 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