linux-kernel - Re: [PATCH 1/1] i3c: master: svc: skip address resend on repeat START

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Message-ID: <87zfg75otk.fsf@bootlin.com>
Date: Wed, 23 Apr 2025 09:17:43 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Frank Li <Frank.Li@....com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
  linux-i3c@...ts.infradead.org (moderated list:SILVACO I3C DUAL-ROLE
 MASTER),  imx@...ts.linux.dev (open list:SILVACO I3C DUAL-ROLE MASTER),
  linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH 1/1] i3c: master: svc: skip address resend on repeat START

On 16/04/2025 at 12:47:50 -04, Frank Li <Frank.Li@....com> wrote:

> According to the I3C specification, address arbitration only happens during
> the START. Repeated START do not initiate arbitration, and In-Band
> Interrupts (IBIs) cannot occur at this stage.
>
> Resending the address upon a NACK in a repeat START is therefore redundant
> and unnecessary. Avoid redundant retries, improving efficiency and ensuring
> protocol compliance.
>
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
>  drivers/i3c/master/svc-i3c-master.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
> index 85e16de208d3b..5212c2cc6855f 100644
> --- a/drivers/i3c/master/svc-i3c-master.c
> +++ b/drivers/i3c/master/svc-i3c-master.c
> @@ -1281,9 +1281,9 @@ static int svc_i3c_master_write(struct svc_i3c_master *master,
>  static int svc_i3c_master_xfer(struct svc_i3c_master *master,
>  			       bool rnw, unsigned int xfer_type, u8 addr,
>  			       u8 *in, const u8 *out, unsigned int xfer_len,
> -			       unsigned int *actual_len, bool continued)
> +			       unsigned int *actual_len, bool continued, bool repeat_start)
>  {
> -	int retry = 2;
> +	int retry = repeat_start ? 1 : 2;
>  	u32 reg;
>  	int ret;
>  
> @@ -1468,7 +1468,7 @@ static void svc_i3c_master_start_xfer_locked(struct svc_i3c_master *master)
>  		ret = svc_i3c_master_xfer(master, cmd->rnw, xfer->type,
>  					  cmd->addr, cmd->in, cmd->out,
>  					  cmd->len, &cmd->actual_len,
> -					  cmd->continued);
> +					  cmd->continued, !!i);

Could we just pass 'i' here? Or maybe 'i > 0' which might be even clearer.

>  		/* cmd->xfer is NULL if I2C or CCC transfer */
>  		if (cmd->xfer)
>  			cmd->xfer->actual_len = cmd->actual_len;

Thanks,
Miquèl