Re: [PATCH v1 1/2] i3c: Remove the const qualifier from i2c_msg pointer in i2c_xfers API

[Mukesh Kumar Savaliya]

Good Change Billy. Thanks for bringing this to i3c.

On 1/21/2025 4:37 PM, Billy Tsai wrote:
> The change is necessary to enable the use of the
> `i2c_get_dma_safe_msg_buf()` API, which requires a non-const
> `struct i2c_msg *` to operate. The `i2c_get_dma_safe_msg_buf()` function
> ensures safe handling of I2C messages when using DMA, making it essential
> for scenarios where DMA transfers are involved. By removing the `const`
> qualifier, this patch allows drivers to prepare and manage DMA-safe
> buffers directly.
>
> Signed-off-by: Billy Tsai <billy_tsai@xxxxxxxxxxxxxx>
> ---
>   drivers/i3c/master/dw-i3c-master.c     | 2 +-
>   drivers/i3c/master/i3c-master-cdns.c   | 2 +-
>   drivers/i3c/master/mipi-i3c-hci/core.c | 2 +-
>   drivers/i3c/master/svc-i3c-master.c    | 2 +-
>   include/linux/i3c/master.h             | 2 +-
>   5 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c
> index d09ea5b6467c..54c7d86997d5 100644
> --- a/drivers/i3c/master/dw-i3c-master.c
> +++ b/drivers/i3c/master/dw-i3c-master.c
> @@ -1079,7 +1079,7 @@ static void dw_i3c_master_detach_i3c_dev(struct i3c_dev_desc *dev)
>   }
>   
>   static int dw_i3c_master_i2c_xfers(struct i2c_dev_desc *dev,
> -				   const struct i2c_msg *i2c_xfers,
> +				   struct i2c_msg *i2c_xfers,
what we need is only i2c_xfers->buf to be DMA-safe, not the *i2c_xfers. 
Right ?

>   				   int i2c_nxfers)
>   {
>   	struct dw_i3c_i2c_dev_data *data = i2c_dev_get_master_data(dev);
> diff --git a/drivers/i3c/master/i3c-master-cdns.c b/drivers/i3c/master/i3c-master-cdns.c
> index 8d69a34986d9..c9e4c129454c 100644
> --- a/drivers/i3c/master/i3c-master-cdns.c
> +++ b/drivers/i3c/master/i3c-master-cdns.c
> @@ -813,7 +813,7 @@ static int cdns_i3c_master_priv_xfers(struct i3c_dev_desc *dev,
>   }
>   
>   static int cdns_i3c_master_i2c_xfers(struct i2c_dev_desc *dev,
> -				     const struct i2c_msg *xfers, int nxfers)
> +				     struct i2c_msg *xfers, int nxfers)

>   {
>   	struct i3c_master_controller *m = i2c_dev_get_master(dev);
>   	struct cdns_i3c_master *master = to_cdns_i3c_master(m);
we only need to use i2c_get_dma_safe_msg_buf() for the xfers[i].buf 
being used inside the driver as a protection ?
Also I guess same change is required for all the vendor drivers. But Not 
sure if it's feasible with this patch ?
> diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
> index e6e482a259b4..a408feac3e9e 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/core.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/core.c
> @@ -367,7 +367,7 @@ static int i3c_hci_priv_xfers(struct i3c_dev_desc *dev,
>   }
>   
>   static int i3c_hci_i2c_xfers(struct i2c_dev_desc *dev,
> -			     const struct i2c_msg *i2c_xfers, int nxfers)
> +			     struct i2c_msg *i2c_xfers, int nxfers)
>   {
>   	struct i3c_master_controller *m = i2c_dev_get_master(dev);
>   	struct i3c_hci *hci = to_i3c_hci(m);
> diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> index c1ee3828e7ee..24bd701b5de0 100644
> --- a/drivers/i3c/master/svc-i3c-master.c
> +++ b/drivers/i3c/master/svc-i3c-master.c
> @@ -1584,7 +1584,7 @@ static int svc_i3c_master_priv_xfers(struct i3c_dev_desc *dev,
>   }
>   
>   static int svc_i3c_master_i2c_xfers(struct i2c_dev_desc *dev,
> -				    const struct i2c_msg *xfers,
> +				    struct i2c_msg *xfers,
>   				    int nxfers)
>   {
>   	struct i3c_master_controller *m = i2c_dev_get_master(dev);
> diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
> index 12d532b012c5..c67922ece617 100644
> --- a/include/linux/i3c/master.h
> +++ b/include/linux/i3c/master.h
> @@ -475,7 +475,7 @@ struct i3c_master_controller_ops {
>   	int (*attach_i2c_dev)(struct i2c_dev_desc *dev);
>   	void (*detach_i2c_dev)(struct i2c_dev_desc *dev);
>   	int (*i2c_xfers)(struct i2c_dev_desc *dev,
> -			 const struct i2c_msg *xfers, int nxfers);
> +			 struct i2c_msg *xfers, int nxfers);
>   	int (*request_ibi)(struct i3c_dev_desc *dev,
>   			   const struct i3c_ibi_setup *req);
>   	void (*free_ibi)(struct i3c_dev_desc *dev);