[PATCH v3 2/4] i3c: mipi-i3c-hci: Use core helpers for DMA mapping and bounce buffering

[Frank Li]

On Wed, Aug 20, 2025 at 02:34:45PM +0300, Jarkko Nikula wrote:
> So far only I3C private and I2C transfers have required a bounce buffer
> for DMA transfers when buffer is not DMA'able.
>
> It was observed that when the device DMA is IOMMU mapped and the receive
> length is not a multiple of DWORDs (32-bit), the last DWORD is padded
> with stale data from the RX FIFO, corrupting 1-3 bytes beyond the
> expected data.
>
> A similar issue, though less severe, occurs when an I3C target returns
> less data than requested. In this case, the padding does not exceed the
> requested number of bytes, assuming the device DMA is not IOMMU mapped.
>
> Therefore, all I3C private transfer, CCC command payload and I2C
> transfer receive buffers must be properly sized for the DMA being IOMMU
> mapped. Even if those buffers are already DMA safe, their size may not
> be DWORD aligned.
>
> To prepare for the device DMA being IOMMU mapped and to address the
> above issue, use helpers from I3C core for DMA mapping and bounce
> buffering for all DMA transfers.
>
> For now, require bounce buffer only when the buffer is in the
> vmalloc() area to avoid unnecessary copying with CCC commands and
> DMA-safe I2C transfers.

I see below you pass 'false' to i3c_master_dma_map_single(). where
check buffer in the vmaloc() area?

>
> Signed-off-by: Jarkko Nikula <jarkko.nikula at linux.intel.com>
> ---
>  drivers/i3c/master/mipi-i3c-hci/core.c | 34 --------------------------
>  drivers/i3c/master/mipi-i3c-hci/dma.c  | 27 +++++++++-----------
>  drivers/i3c/master/mipi-i3c-hci/hci.h  |  3 +--
>  3 files changed, 12 insertions(+), 52 deletions(-)
>
[...]
> @@ -391,21 +390,17 @@ static int hci_dma_queue_xfer(struct i3c_hci *hci,
>
>  		/* 2nd and 3rd words of Data Buffer Descriptor Structure */
>  		if (xfer->data) {
> -			buf = xfer->bounce_buf ? xfer->bounce_buf : xfer->data;
> -			xfer->data_dma =
> -				dma_map_single(&hci->master.dev,
> -					       buf,
> -					       xfer->data_len,
> -					       xfer->rnw ?
> -						  DMA_FROM_DEVICE :
> -						  DMA_TO_DEVICE);
> -			if (dma_mapping_error(&hci->master.dev,
> -					      xfer->data_dma)) {
> +			xfer->dma = i3c_master_dma_map_single(&hci->master.dev,
> +							      xfer->data,
> +							      xfer->data_len,
> +							      false,
> +

you pass false here.

Frank
					      dir);
> +			if (!xfer->dma) {
>  				hci_dma_unmap_xfer(hci, xfer_list, i);
>  				return -ENOMEM;
>  			}
> -			*ring_data++ = lower_32_bits(xfer->data_dma);
> -			*ring_data++ = upper_32_bits(xfer->data_dma);
> +			*ring_data++ = lower_32_bits(xfer->dma->addr);
> +			*ring_data++ = upper_32_bits(xfer->dma->addr);
>  		} else {
>  			*ring_data++ = 0;
>  			*ring_data++ = 0;
> diff --git a/drivers/i3c/master/mipi-i3c-hci/hci.h b/drivers/i3c/master/mipi-i3c-hci/hci.h
> index 69ea1d10414b..33bc4906df1f 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/hci.h
> +++ b/drivers/i3c/master/mipi-i3c-hci/hci.h
> @@ -94,8 +94,7 @@ struct hci_xfer {
>  		};
>  		struct {
>  			/* DMA specific */
> -			dma_addr_t data_dma;
> -			void *bounce_buf;
> +			struct i3c_dma *dma;
>  			int ring_number;
>  			int ring_entry;
>  		};
> --
> 2.47.2
>
>
> --
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