Re: [PATCH 13/17] i3c: mipi-i3c-hci: Remove invalid transfer size limit

[Frank Li]

On Mon, Sep 14, 2026 at 02:29:59PM +0300, Adrian Hunter wrote:
> The driver derives a maximum transfer size from
> HC_CAP_MAX_DATA_LENGTH in HC_CAPABILITIES, but no published version of
> the I3C HCI specification defines such a field.
>
> HC_CAPABILITIES reserves Bits[31:8] in HCI v1.0 and Bits[27:22] in HCI
> v1.1 and v1.2, so the bits used by HC_CAP_MAX_DATA_LENGTH are reserved
> in all released HCI versions.  Neither the HCI nor the I3C TCRI
> specifications define a maximum data length capability.
>
> On compliant controllers reserved bits read as zero, making the
> computed limit 65536 bytes.  Since struct i3c_xfer.len is u16,
> transfers can never reach that size and the resulting -EFBIG check can
> never trigger.
>
> Remove the unused capability definition and the dead size check.
>
> The driver's effective limit remains unchanged. HCI specifications
> define DATA_LENGTH as a 16-bit field and require larger transfers to be
> split across multiple Transfer Descriptors.  The driver already relies
> on the core's 16-bit length types elsewhere when constructing
> descriptors.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/i3c/master/mipi-i3c-hci/core.c | 7 -------
>  1 file changed, 7 deletions(-)
>
> diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
> index b9b20797d045..4629a16debc9 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/core.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/core.c
> @@ -51,7 +51,6 @@
>  #define HC_CAP_SG_DC_EN			BIT(30)
>  #define HC_CAP_SG_IBI_EN		BIT(29)
>  #define HC_CAP_SG_CR_EN			BIT(28)
> -#define HC_CAP_MAX_DATA_LENGTH		GENMASK(24, 22)
>  #define HC_CAP_CMD_SIZE			GENMASK(21, 20)
>  #define HC_CAP_DIRECT_COMMANDS_EN	BIT(18)
>  #define HC_CAP_MULTI_LANE_EN		BIT(15)
> @@ -473,7 +472,6 @@ static int i3c_hci_i3c_xfers(struct i3c_dev_desc *dev,
>  	struct i3c_hci *hci = to_i3c_hci(m);
>  	struct hci_xfer *xfer;
>  	DECLARE_COMPLETION_ONSTACK(done);
> -	unsigned int size_limit;
>  	int i, last, ret = 0;
>
>  	dev_dbg(&hci->master.dev, "nxfers = %d", nxfers);
> @@ -482,13 +480,8 @@ static int i3c_hci_i3c_xfers(struct i3c_dev_desc *dev,
>  	if (!xfer)
>  		return -ENOMEM;
>
> -	size_limit = 1U << (16 + FIELD_GET(HC_CAP_MAX_DATA_LENGTH, hci->caps));
> -
>  	for (i = 0; i < nxfers; i++) {
>  		xfer[i].data_len = i3c_xfers[i].len;
> -		ret = -EFBIG;
> -		if (xfer[i].data_len >= size_limit)
> -			goto out;
>  		xfer[i].rnw = i3c_xfers[i].rnw;
>  		if (i3c_xfers[i].rnw) {
>  			xfer[i].data = i3c_xfers[i].data.in;
> --
> 2.53.0
>