Re: [PATCH] dmaengine: qcom: gpi: Set IEOB on linked I2C GO TRE to retire TX descriptor

[Dmitry Baryshkov]

On Thu, Sep 10, 2026 at 12:53:32AM +0700, Vsevolod Nevorotov wrote:
> In GPI mode, an I2C read transaction consists of a command phase on the
> TX channel (issuing CONFIG0 and GO TREs) linked to a data phase on the RX
> channel (issuing the DMA TRE to receive data).
> 
> Commit 656147fb1d4c ("i2c: qcom-geni: Avoid extra TX DMA TRE for single
> read message in GPI mode") avoided programming a dummy TX DMA TRE for read
> messages, leaving only the GO TRE on the TX channel with the TRE_FLAGS_LINK
> flag set.
> 
> However, gpi_create_i2c_tre() did not set TRE_FLAGS_IEOB (Interrupt on End
> of Block) on the linked GO TRE. Because no TRE on the TX channel has an
> interrupt flag set, GSI hardware never generates a completion event on
> the TX channel when the GO command finishes. As a result, the TX transfer
> ring read pointer is never advanced and TX descriptors are never retired.
> 
> Under sustained or high-frequency traffic (such as touchscreen controllers
> operating at 120-240 Hz), the TX transfer ring quickly runs out of slots:
>   gpi 900000.dma-controller: not enough space in ring, avail:1 required:3
>   geni_i2c 990000.i2c: prep_slave_sg failed
>   geni_i2c 990000.i2c: GPI transfer failed: -5
> 
> Fix this properly by setting TRE_FLAGS_IEOB on the GO TRE when multi_msg
> is true (matching Qualcomm's hardware specification and the existing SPI
> implementation in gpi_create_spi_tre). When the hardware finishes executing
> the GO command block, it generates an MSM_GPI_TCE_EOB event on the TX
> channel. In gpi_process_xfer_compl_event(), handle MSM_GPI_TCE_EOB for
> linked I2C command descriptors without a subsequent TX DMA TRE by
> retiring the descriptor and updating the cookie without invoking the
> client callback, allowing the linked RX channel's DMA completion
> (MSM_GPI_TCE_EOT) to signal final transfer completion to the client.
> Other EOB events fall through to the default transfer completion path.
> 
> Fixes: 656147fb1d4c ("i2c: qcom-geni: Avoid extra TX DMA TRE for single read message in GPI mode")
> Signed-off-by: Vsevolod Nevorotov <sevanevorotov29@xxxxxxxxx>
> ---
>  drivers/dma/qcom/gpi.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>


-- 
With best wishes
Dmitry