[PATCH v5 3/5] i3c: use actual_len for read transfers
Adrian Hunter
adrian.hunter at intel.com
Thu Sep 24 04:53:54 PDT 2026
On 22/09/2026 02:06, Sam Agazaryan wrote:
> Currently only the amd and svc I3C controller drivers populate
> i3c_xfer.actual_len on reads, while dw-i3c-master and mipi-i3c-hci
> overwrite i3c_xfer.len with the received byte count and leave actual_len
> as 0. Because of this inconsistency, mctp-i3c reads xfer.len instead of
> xfer.actual_len, making it fail on controllers that do not mutate len.
>
> Unify read length reporting across the subsystem:
> - Clarify in <linux/i3c/device.h> that actual_len reflects the actual
> number of bytes transferred on reads.
> - Update adi, cdns, dw, mipi-i3c-hci, and renesas controller drivers to
> populate actual_len on read transfers without mutating len.
> - Update mctp-i3c to read xfer.actual_len instead of xfer.len.
>
> Co-developed-by: Meagan Lloyd <meaganlloyd at linux.microsoft.com>
> Signed-off-by: Meagan Lloyd <meaganlloyd at linux.microsoft.com>
> Signed-off-by: Sam Agazaryan <samagazaryan at google.com>
Looks good.
1 issue from Sashiko:
https://sashiko.dev/#/patchset/20260921230603.2518652-1-samagazaryan%40google.com?part=3
Also i3c_dev_do_xfers_locked() should probably clamp actual_len to len.
> ---
> drivers/i3c/master/adi-i3c-master.c | 5 ++++-
> drivers/i3c/master/dw-i3c-master.c | 2 +-
> drivers/i3c/master/i3c-master-cdns.c | 5 ++++-
> drivers/i3c/master/mipi-i3c-hci/core.c | 2 +-
> drivers/i3c/master/renesas-i3c.c | 3 +++
> drivers/net/mctp/mctp-i3c.c | 10 +++++-----
> include/linux/i3c/device.h | 2 +-
> 7 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/i3c/master/adi-i3c-master.c b/drivers/i3c/master/adi-i3c-master.c
> index b35386260350..d033bfd4ecc2 100644
> --- a/drivers/i3c/master/adi-i3c-master.c
> +++ b/drivers/i3c/master/adi-i3c-master.c
> @@ -412,8 +412,11 @@ static int adi_i3c_master_i3c_xfers(struct i3c_dev_desc *dev,
>
> ret = xfer->ret;
>
> - for (i = 0; i < nxfers; i++)
> + for (i = 0; i < nxfers; i++) {
> xfers[i].err = adi_i3c_cmd_get_err(&xfer->cmds[i]);
> + if (xfers[i].rnw)
> + xfers[i].actual_len = xfer->cmds[i].rx_len;
> + }
>
> return ret;
> }
> diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c
> index 4563d8761ba0..28e8eb293747 100644
> --- a/drivers/i3c/master/dw-i3c-master.c
> +++ b/drivers/i3c/master/dw-i3c-master.c
> @@ -1029,7 +1029,7 @@ static int dw_i3c_master_i3c_xfers(struct i3c_dev_desc *dev,
> struct dw_i3c_cmd *cmd = &xfer->cmds[i];
>
> if (i3c_xfers[i].rnw)
> - i3c_xfers[i].len = cmd->rx_len;
> + i3c_xfers[i].actual_len = cmd->rx_len;
> }
>
> ret = xfer->ret;
> diff --git a/drivers/i3c/master/i3c-master-cdns.c b/drivers/i3c/master/i3c-master-cdns.c
> index 2d98c1ce9b12..331062c10b31 100644
> --- a/drivers/i3c/master/i3c-master-cdns.c
> +++ b/drivers/i3c/master/i3c-master-cdns.c
> @@ -795,8 +795,11 @@ static int cdns_i3c_master_i3c_xfers(struct i3c_dev_desc *dev,
>
> ret = cdns_xfer->ret;
>
> - for (i = 0; i < nxfers; i++)
> + for (i = 0; i < nxfers; i++) {
> xfers[i].err = cdns_i3c_cmd_get_err(&cdns_xfer->cmds[i]);
> + if (xfers[i].rnw)
> + xfers[i].actual_len = cdns_xfer->cmds[i].rx_len;
> + }
>
> cdns_i3c_master_free_xfer(cdns_xfer);
>
> diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
> index dadf049bd4b5..f74c02fab9e3 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/core.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/core.c
> @@ -509,7 +509,7 @@ static int i3c_hci_i3c_xfers(struct i3c_dev_desc *dev,
> goto out;
> for (i = 0; i < nxfers; i++) {
> if (i3c_xfers[i].rnw)
> - i3c_xfers[i].len = RESP_DATA_LENGTH(xfer[i].response);
> + i3c_xfers[i].actual_len = RESP_DATA_LENGTH(xfer[i].response);
> if (RESP_STATUS(xfer[i].response) != RESP_SUCCESS) {
> ret = -EIO;
> goto out;
> diff --git a/drivers/i3c/master/renesas-i3c.c b/drivers/i3c/master/renesas-i3c.c
> index 28c0927a0179..a3dcb4cd9b0e 100644
> --- a/drivers/i3c/master/renesas-i3c.c
> +++ b/drivers/i3c/master/renesas-i3c.c
> @@ -918,6 +918,9 @@ static int renesas_i3c_i3c_xfers(struct i3c_dev_desc *dev, struct i3c_xfer *i3c_
> time_left = renesas_i3c_wait_xfer(i3c, xfer);
> if (!time_left)
> xfer_failed = true;
> +
> + if (i3c_xfers[i].rnw)
> + i3c_xfers[i].actual_len = cmd->rx_count;
> }
>
> if (xfer_failed)
> diff --git a/drivers/net/mctp/mctp-i3c.c b/drivers/net/mctp/mctp-i3c.c
> index 6d2bbae7477b..5f94c11a1712 100644
> --- a/drivers/net/mctp/mctp-i3c.c
> +++ b/drivers/net/mctp/mctp-i3c.c
> @@ -131,12 +131,12 @@ static int mctp_i3c_read(struct mctp_i3c_device *mi)
> if (rc < 0)
> goto err;
>
> - if (WARN_ON_ONCE(xfer.len > mi->mrl)) {
> + if (WARN_ON_ONCE(xfer.actual_len > mi->mrl)) {
> /* Bad i3c bus driver */
> rc = -EIO;
> goto err;
> }
> - if (xfer.len < MCTP_I3C_MINLEN) {
> + if (xfer.actual_len < MCTP_I3C_MINLEN) {
> stats->rx_length_errors++;
> rc = -EIO;
> goto err;
> @@ -145,15 +145,15 @@ static int mctp_i3c_read(struct mctp_i3c_device *mi)
> /* check PEC, including address byte */
> addr = mi->addr << 1 | 1;
> pec = i2c_smbus_pec(0, &addr, 1);
> - pec = i2c_smbus_pec(pec, xfer.data.in, xfer.len - 1);
> - if (pec != ((u8 *)xfer.data.in)[xfer.len - 1]) {
> + pec = i2c_smbus_pec(pec, xfer.data.in, xfer.actual_len - 1);
> + if (pec != ((u8 *)xfer.data.in)[xfer.actual_len - 1]) {
> stats->rx_crc_errors++;
> rc = -EINVAL;
> goto err;
> }
>
> /* Remove PEC */
> - skb_trim(skb, xfer.len - 1);
> + skb_trim(skb, xfer.actual_len - 1);
>
> cb = __mctp_cb(skb);
> cb->halen = PID_SIZE;
> diff --git a/include/linux/i3c/device.h b/include/linux/i3c/device.h
> index 971d53349b6f..f868a7bf2bc9 100644
> --- a/include/linux/i3c/device.h
> +++ b/include/linux/i3c/device.h
> @@ -59,7 +59,7 @@ enum i3c_xfer_mode {
> * @rnw: encodes the transfer direction. true for a read, false for a write
> * @cmd: Read/Write command in HDR mode, read: 0x80 - 0xff, write: 0x00 - 0x7f
> * @len: transfer length in bytes of the transfer
> - * @actual_len: actual length in bytes are transferred by the controller
> + * @actual_len: actual length in bytes transferred by the controller on read
> * @data: input/output buffer
> * @data.in: input buffer. Must point to a DMA-able buffer
> * @data.out: output buffer. Must point to a DMA-able buffer
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