Re: [PATCH v2] i2c: stm32f7: Add atomic_xfer method to driver

Alain Volmat
2023-08-02T10:07:55Z

Hi Sean,

sorry for the delay for this review. Thank you Andi for
the review as well.

Few other comments in addition to what Andi already mentioned.

On Tue, Jul 18, 2023 at 12:54:35PM +0200, Sean Nyekjaer wrote:
> Add an atomic_xfer method to the driver so that it behaves correctly
> when controlling a PMIC that is responsible for device shutdown.
>
> The atomic_xfer method added is similar to the one from the i2c-mv64xxx
> driver. When running an atomic_xfer a bool flag in the driver data is
> set, the interrupt is not unmasked on transfer start, and the IRQ
> handler is manually invoked while waiting for pending transfers to
> complete.
>
> Signed-off-by: Sean Nyekjaer <sean@geanix.com>
> ---
> Changes since v1:
> - Removed dma in atomic
>
> drivers/i2c/busses/i2c-stm32f7.c | 111 ++++++++++++++++++++++---------
> 1 file changed, 78 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
> index e897d9101434..d944b8f85d1c 100644
> --- a/drivers/i2c/busses/i2c-stm32f7.c
> +++ b/drivers/i2c/busses/i2c-stm32f7.c
> @@ -357,6 +357,7 @@ struct stm32f7_i2c_dev {
> u32 dnf_dt;
> u32 dnf;
> struct stm32f7_i2c_alert *alert;
> + bool atomic;

I am wondering if this atomic really needs to be within the struct.
It could well be given as last arg of stm32f7_i2c_xfer_core and
stm32f7_i2c_xfer functions.

> };
>
> /*
> @@ -905,38 +906,43 @@ static void stm32f7_i2c_xfer_msg(struct stm32f7_i2c_dev *i2c_dev,
> cr2 |= STM32F7_I2C_CR2_NBYTES(f7_msg->count);
> }
>
> - /* Enable NACK, STOP, error and transfer complete interrupts */
> - cr1 |= STM32F7_I2C_CR1_ERRIE | STM32F7_I2C_CR1_TCIE |
> - STM32F7_I2C_CR1_STOPIE | STM32F7_I2C_CR1_NACKIE;
> -
> - /* Clear DMA req and TX/RX interrupt */
> - cr1 &= ~(STM32F7_I2C_CR1_RXIE | STM32F7_I2C_CR1_TXIE |
> - STM32F7_I2C_CR1_RXDMAEN | STM32F7_I2C_CR1_TXDMAEN);
> -
> - /* Configure DMA or enable RX/TX interrupt */
> - i2c_dev->use_dma = false;
> - if (i2c_dev->dma && f7_msg->count >= STM32F7_I2C_DMA_LEN_MIN) {
> - ret = stm32_i2c_prep_dma_xfer(i2c_dev->dev, i2c_dev->dma,
> - msg->flags & I2C_M_RD,
> - f7_msg->count, f7_msg->buf,
> - stm32f7_i2c_dma_callback,
> - i2c_dev);
> - if (!ret)
> - i2c_dev->use_dma = true;
> - else
> - dev_warn(i2c_dev->dev, "can't use DMA\n");
> - }
> + if (!i2c_dev->atomic) {
> + /* Enable NACK, STOP, error and transfer complete interrupts */
> + cr1 |= STM32F7_I2C_CR1_ERRIE | STM32F7_I2C_CR1_TCIE |
> + STM32F7_I2C_CR1_STOPIE | STM32F7_I2C_CR1_NACKIE;
> +
> + /* Clear DMA req and TX/RX interrupt */
> + cr1 &= ~(STM32F7_I2C_CR1_RXIE | STM32F7_I2C_CR1_TXIE |
> + STM32F7_I2C_CR1_RXDMAEN | STM32F7_I2C_CR1_TXDMAEN);
> +
> + /* Configure DMA or enable RX/TX interrupt */
> + i2c_dev->use_dma = false;
> + if (i2c_dev->dma && f7_msg->count >= STM32F7_I2C_DMA_LEN_MIN) {
> + ret = stm32_i2c_prep_dma_xfer(i2c_dev->dev, i2c_dev->dma,
> + msg->flags & I2C_M_RD,
> + f7_msg->count, f7_msg->buf,
> + stm32f7_i2c_dma_callback,
> + i2c_dev);
> + if (!ret)
> + i2c_dev->use_dma = true;
> + else
> + dev_warn(i2c_dev->dev, "can't use DMA\n");
> + }
>
> - if (!i2c_dev->use_dma) {
> - if (msg->flags & I2C_M_RD)
> - cr1 |= STM32F7_I2C_CR1_RXIE;
> - else
> - cr1 |= STM32F7_I2C_CR1_TXIE;
> + if (!i2c_dev->use_dma) {
> + if (msg->flags & I2C_M_RD)
> + cr1 |= STM32F7_I2C_CR1_RXIE;
> + else
> + cr1 |= STM32F7_I2C_CR1_TXIE;
> + } else {
> + if (msg->flags & I2C_M_RD)
> + cr1 |= STM32F7_I2C_CR1_RXDMAEN;
> + else
> + cr1 |= STM32F7_I2C_CR1_TXDMAEN;
> + }
> } else {
> - if (msg->flags & I2C_M_RD)
> - cr1 |= STM32F7_I2C_CR1_RXDMAEN;
> - else
> - cr1 |= STM32F7_I2C_CR1_TXDMAEN;
> + /* Disable all interrupts */
> + cr1 &= ~STM32F7_I2C_ALL_IRQ_MASK;
> }
>
> /* Configure Start/Repeated Start */
> @@ -1670,7 +1676,22 @@ static irqreturn_t stm32f7_i2c_isr_error(int irq, void *data)
> return IRQ_HANDLED;
> }
>
> -static int stm32f7_i2c_xfer(struct i2c_adapter *i2c_adap,
> +static int stm32f7_i2c_wait_polling(struct stm32f7_i2c_dev *i2c_dev)
> +{
> + ktime_t timeout = ktime_add_ms(ktime_get(), i2c_dev->adap.timeout);
> +
> + while (ktime_compare(ktime_get(), timeout) < 0) {
> + udelay(5);
> + stm32f7_i2c_isr_event(0, i2c_dev);
> +
> + if (try_wait_for_completion(&i2c_dev->complete))
> + return 1;

I agree with the complete / wait_for_completion approach since it allows
to keep most of code common by manually calling the isr_event for
checking status bits. However what about using completion_done instead
of try_wait_for_completion here ? This shouldn't change much since
anyway there is a reinit_completion at the beginning of the xfer
function, but at least function naming feels better since not refering
to waiting ..

> + }
> +
> + return 0;
> +}
> +
> +static int stm32f7_i2c_xfer_core(struct i2c_adapter *i2c_adap,
> struct i2c_msg msgs[], int num)
> {
> struct stm32f7_i2c_dev *i2c_dev = i2c_get_adapdata(i2c_adap);
> @@ -1694,8 +1715,13 @@ static int stm32f7_i2c_xfer(struct i2c_adapter *i2c_adap,
>
> stm32f7_i2c_xfer_msg(i2c_dev, msgs);
>
> - time_left = wait_for_completion_timeout(&i2c_dev->complete,
> - i2c_dev->adap.timeout);
> + if (!i2c_dev->atomic) {
> + time_left = wait_for_completion_timeout(&i2c_dev->complete,
> + i2c_dev->adap.timeout);
> + } else {
> + time_left = stm32f7_i2c_wait_polling(i2c_dev);
> + }
> +
> ret = f7_msg->result;
> if (ret) {
> if (i2c_dev->use_dma)
> @@ -1727,6 +1753,24 @@ static int stm32f7_i2c_xfer(struct i2c_adapter *i2c_adap,
> return (ret < 0) ? ret : num;
> }
>
> +static int stm32f7_i2c_xfer(struct i2c_adapter *i2c_adap,
> + struct i2c_msg msgs[], int num)
> +{
> + struct stm32f7_i2c_dev *i2c_dev = i2c_get_adapdata(i2c_adap);
> +
> + i2c_dev->atomic = 0;
> + return stm32f7_i2c_xfer_core(i2c_adap, msgs, num);
> +}
> +
> +static int stm32f7_i2c_xfer_atomic(struct i2c_adapter *i2c_adap,
> + struct i2c_msg msgs[], int num)
> +{
> + struct stm32f7_i2c_dev *i2c_dev = i2c_get_adapdata(i2c_adap);
> +
> + i2c_dev->atomic = 1;
> + return stm32f7_i2c_xfer_core(i2c_adap, msgs, num);
> +}
> +
> static int stm32f7_i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
> unsigned short flags, char read_write,
> u8 command, int size,
> @@ -2095,6 +2139,7 @@ static u32 stm32f7_i2c_func(struct i2c_adapter *adap)
>
> static const struct i2c_algorithm stm32f7_i2c_algo = {
> .master_xfer = stm32f7_i2c_xfer,
> + .master_xfer_atomic = stm32f7_i2c_xfer_atomic,
> .smbus_xfer = stm32f7_i2c_smbus_xfer,
> .functionality = stm32f7_i2c_func,
> .reg_slave = stm32f7_i2c_reg_slave,
> --

Regards,
Alain

> 2.40.0
>