Re: [PATCH 03/12] i2c: core: introduce callbacks for atomic transfers

[Andy Shevchenko]

On Wed, Apr 3, 2019 at 3:43 PM Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> We had the request to access devices very late when interrupts are not
> available anymore multiple times now. Mostly to prepare shutdown or
> reboot. Allow adapters to specify a specific callback for this case.
> Note that we fall back to the generic {master|smbus}_xfer callback if
> this new atomic one is not present. This is intentional to preserve the
> previous behaviour and avoid regressions. Because there are drivers not
> using interrupts or because it might have worked "accidently" before.
>

Reviewed-by Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

> Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/i2c/i2c-core-base.c  |  6 +++++-
>  drivers/i2c/i2c-core-smbus.c | 18 ++++++++++++++----
>  drivers/i2c/i2c-core.h       |  7 +++++--
>  include/linux/i2c.h          | 15 ++++++++++++---
>  4 files changed, 36 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index ad14f38a67e4..4e6300dc2c4e 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -1890,7 +1890,11 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>         /* Retry automatically on arbitration loss */
>         orig_jiffies = jiffies;
>         for (ret = 0, try = 0; try <= adap->retries; try++) {
> -               ret = adap->algo->master_xfer(adap, msgs, num);
> +               if (i2c_in_atomic_xfer_mode() && adap->algo->master_xfer_atomic)
> +                       ret = adap->algo->master_xfer_atomic(adap, msgs, num);
> +               else
> +                       ret = adap->algo->master_xfer(adap, msgs, num);
> +
>                 if (ret != -EAGAIN)
>                         break;
>                 if (time_after(jiffies, orig_jiffies + adap->timeout))
> diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> index 357e083e8f45..fdb0fb9fb9aa 100644
> --- a/drivers/i2c/i2c-core-smbus.c
> +++ b/drivers/i2c/i2c-core-smbus.c
> @@ -548,6 +548,9 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
>                      unsigned short flags, char read_write,
>                      u8 command, int protocol, union i2c_smbus_data *data)
>  {
> +       int (*xfer_func)(struct i2c_adapter *adap, u16 addr,
> +                        unsigned short flags, char read_write,
> +                        u8 command, int size, union i2c_smbus_data *data);
>         unsigned long orig_jiffies;
>         int try;
>         s32 res;
> @@ -562,13 +565,20 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
>
>         flags &= I2C_M_TEN | I2C_CLIENT_PEC | I2C_CLIENT_SCCB;
>
> -       if (adapter->algo->smbus_xfer) {
> +       xfer_func = adapter->algo->smbus_xfer;
> +       if (i2c_in_atomic_xfer_mode()) {
> +               if (adapter->algo->smbus_xfer_atomic)
> +                       xfer_func = adapter->algo->smbus_xfer_atomic;
> +               else if (adapter->algo->master_xfer_atomic)
> +                       xfer_func = NULL; /* fallback to I2C emulation */
> +       }
> +
> +       if (xfer_func) {
>                 /* Retry automatically on arbitration loss */
>                 orig_jiffies = jiffies;
>                 for (res = 0, try = 0; try <= adapter->retries; try++) {
> -                       res = adapter->algo->smbus_xfer(adapter, addr, flags,
> -                                                       read_write, command,
> -                                                       protocol, data);
> +                       res = xfer_func(adapter, addr, flags, read_write,
> +                                       command, protocol, data);
>                         if (res != -EAGAIN)
>                                 break;
>                         if (time_after(jiffies,
> diff --git a/drivers/i2c/i2c-core.h b/drivers/i2c/i2c-core.h
> index deea47c576e5..f9d0c417b5a5 100644
> --- a/drivers/i2c/i2c-core.h
> +++ b/drivers/i2c/i2c-core.h
> @@ -43,10 +43,13 @@ static inline int __i2c_lock_bus_helper(struct i2c_adapter *adap)
>  {
>         int ret = 0;
>
> -       if (i2c_in_atomic_xfer_mode())
> +       if (i2c_in_atomic_xfer_mode()) {
> +               WARN(!adap->algo->master_xfer_atomic && !adap->algo->smbus_xfer_atomic,
> +                    "No atomic I2C transfer handler for '%s'\n", dev_name(&adap->dev));
>                 ret = i2c_trylock_bus(adap, I2C_LOCK_SEGMENT) ? 0 : -EAGAIN;
> -       else
> +       } else {
>                 i2c_lock_bus(adap, I2C_LOCK_SEGMENT);
> +       }
>
>         return ret;
>  }
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 758a6db864c9..03755d4c9229 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -499,9 +499,13 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info,
>   * @master_xfer: Issue a set of i2c transactions to the given I2C adapter
>   *   defined by the msgs array, with num messages available to transfer via
>   *   the adapter specified by adap.
> + * @master_xfer_atomic: same as @master_xfer. Yet, only using atomic context
> + *   so e.g. PMICs can be accessed very late before shutdown. Optional.
>   * @smbus_xfer: Issue smbus transactions to the given I2C adapter. If this
>   *   is not present, then the bus layer will try and convert the SMBus calls
>   *   into I2C transfers instead.
> + * @smbus_xfer_atomic: same as @smbus_xfer. Yet, only using atomic context
> + *   so e.g. PMICs can be accessed very late before shutdown. Optional.
>   * @functionality: Return the flags that this algorithm/adapter pair supports
>   *   from the I2C_FUNC_* flags.
>   * @reg_slave: Register given client to I2C slave mode of this adapter
> @@ -512,9 +516,9 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info,
>   * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584
>   * to name two of the most common.
>   *
> - * The return codes from the @master_xfer field should indicate the type of
> - * error code that occurred during the transfer, as documented in the kernel
> - * Documentation file Documentation/i2c/fault-codes.
> + * The return codes from the @master_xfer{_atomic} fields should indicate the
> + * type of error code that occurred during the transfer, as documented in the
> + * Kernel Documentation file Documentation/i2c/fault-codes.
>   */
>  struct i2c_algorithm {
>         /*
> @@ -528,9 +532,14 @@ struct i2c_algorithm {
>          */
>         int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,
>                            int num);
> +       int (*master_xfer_atomic)(struct i2c_adapter *adap,
> +                                  struct i2c_msg *msgs, int num);
>         int (*smbus_xfer)(struct i2c_adapter *adap, u16 addr,
>                           unsigned short flags, char read_write,
>                           u8 command, int size, union i2c_smbus_data *data);
> +       int (*smbus_xfer_atomic)(struct i2c_adapter *adap, u16 addr,
> +                                unsigned short flags, char read_write,
> +                                u8 command, int size, union i2c_smbus_data *data);
>
>         /* To determine what the adapter supports */
>         u32 (*functionality)(struct i2c_adapter *adap);
> --
> 2.11.0
>


-- 
With Best Regards,
Andy Shevchenko