Re: [PATCH v1 2/2] i3c: mipi-i3c-hci: Use DMA-safe buffer for I2C transfers

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

On 1/21/25 1:07 PM, Billy Tsai wrote:
> The i2c_get_dma_safe_msg_buf function is used to ensure safe handling of
> I2C messages in HCI DMA mode.
> 
> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
> ---
>   drivers/i3c/master/mipi-i3c-hci/core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
> index a408feac3e9e..3567cd566339 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/core.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/core.c
> @@ -382,7 +382,7 @@ static int i3c_hci_i2c_xfers(struct i2c_dev_desc *dev,
>   		return -ENOMEM;
>   
>   	for (i = 0; i < nxfers; i++) {
> -		xfer[i].data = i2c_xfers[i].buf;
> +		xfer[i].data = i2c_get_dma_safe_msg_buf(&i2c_xfers[i], 1);
>   		xfer[i].data_len = i2c_xfers[i].len;
>   		xfer[i].rnw = i2c_xfers[i].flags & I2C_M_RD;
>   		hci->cmd->prep_i2c_xfer(hci, dev, &xfer[i]);

This allow to remove calls to i3c_hci_alloc_safe_xfer_buf() and 
i3c_hci_free_safe_xfer_buf() in i3c_hci_i2c_xfers().

I was pondering the i2c_get_dma_safe_msg_buf() when making commit 
4afd72876942 ("i3c: mipi-i3c-hci: Add DMA bounce buffer for private 
transfers") but decided to reuse the same (own) helper for both 
i3c_hci_priv_xfers() and i3c_hci_i2c_xfers().

In that sense I'd modify the commit log a bit that instead of ensuring 
safe handling patch switches from custom helper to 
i2c_get_dma_safe_msg_buf() and i2c_put_dma_safe_msg_buf() (please note 
the comment from Wolfram).