linux-kernel - Re: [v5 resend 3/6] i3c: add actual_len in i3c_priv

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Date: Wed, 20 Dec 2023 09:55:26 +0800
From: Joshua Yeong <joshua.yeong@...rfivetech.com>
To: Frank Li <Frank.Li@....com>, <miquel.raynal@...tlin.com>
CC: <alexandre.belloni@...tlin.com>, <conor.culhane@...vaco.com>,
	<imx@...ts.linux.dev>, <joe@...ches.com>, <linux-i3c@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <zbigniew.lukwinski@...ux.intel.com>
Subject: Re: [v5 resend 3/6] i3c: add actual_len in i3c_priv_xfer


On 02/12/2023 6:25 AM, Frank Li wrote:
> In MIPI I3C Specification:
>
> "Ninth Bit of SDR Target Returned (Read) Data as End-of-Data: In I2C, the
> ninth Data bit from Target to Controller is an ACK by the Controller. By
> contrast, in I3C this bit allows the Target to end a Read, and allows the
> Controller to Abort a Read. In SDR terms, the ninth bit of Read data is
> referred to as the T-Bit (for ‘Transition’)"
>
> I3C allow devices early terminate data transfer. So need "actual_len" field
> to indicate how much get by i3c_priv_xfer.
>
> Reviewed-by: Miquel Raynal <miquel.raynal@...tlin.com>
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
>
> Notes:
>      change from v4 to v5
>      - Add Miquel review tag
>
>   include/linux/i3c/device.h | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/i3c/device.h b/include/linux/i3c/device.h
> index 90fa83464f003..ef6217da8253b 100644
> --- a/include/linux/i3c/device.h
> +++ b/include/linux/i3c/device.h
> @@ -54,6 +54,7 @@ enum i3c_hdr_mode {
>    * struct i3c_priv_xfer - I3C SDR private transfer
>    * @rnw: encodes the transfer direction. true for a read, false for a write
>    * @len: transfer length in bytes of the transfer
> + * @actual_len: actual length in bytes are transferred by the controller
>    * @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
> @@ -62,6 +63,7 @@ enum i3c_hdr_mode {
>   struct i3c_priv_xfer {
>   	u8 rnw;
>   	u16 len;
What happens if I3C device does not terminate the T-Bit because it 
expects extra length from master?
> +	u16 actual_len;
>   	union {
>   		void *in;
>   		const void *out;