Re: [PATCH V4] i2c: qcom-geni: Avoid extra TX DMA TRE for single read message in GPI mode

[Mukesh Kumar Savaliya <quic_msavaliy@quicinc.com>]

On 4/10/2026 3:49 PM, Aniket Randive wrote:
> In GPI mode, the I2C GENI driver programs an extra TX DMA transfer
> descriptor (TRE) on the TX channel when handling a single read message.
> This results in an unintended write phase being issued on the I2C bus,
> even though a read transaction does not require any TX data.
> 
> For a single-byte read, the correct hardware sequence consists of the
> CONFIG and GO commands followed by a single RX DMA TRE. Programming an
> additional TX DMA TRE is redundant, causes unnecessary DMA buffer
> mapping on the TX channel, and may lead to incorrect bus behavior.
> 
> Update the transfer logic to avoid programming a TX DMA TRE for single
> read messages in GPI mode.
> 
> Co-developed-by: Maramaina Naresh <naresh.maramaina@oss.qualcomm.com>
> Signed-off-by: Maramaina Naresh <naresh.maramaina@oss.qualcomm.com>
> Signed-off-by: Aniket Randive <aniket.randive@oss.qualcomm.com>
Reviewed-by: Mukesh Kumar Savaliya <mukesh.savaliya@oss.qualcomm.com>
> ---
> 
> Changes in v4:
>    - Added some more description in comment and changed the label name.
> Changes in v3:
>    - Added comment in the driver for better readability and changed the
>      position of 'skip_dma' label to allow dma engine configuration.
> Changes in v2:
>    - Updated the commit message.
> 
>   drivers/i2c/busses/i2c-qcom-geni.c | 24 +++++++++++++++++++-----
>   1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> index a4acb78fafb6..a482a4c60744 100644
> --- a/drivers/i2c/busses/i2c-qcom-geni.c
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -625,8 +625,8 @@ static int geni_i2c_gpi(struct geni_i2c_dev *gi2c, struct i2c_msg msgs[],

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