RE: [PATCH 6.1.y-cip] i3c: master: dw: stop hardcoding initial speed

Hi all,

I sent this to the wrong TO.
Please ignore it.

Best regards,
  Nobuhiro

> -----Original Message-----
> From: Nobuhiro Iwamatsu <[email protected]>
> Sent: Tuesday, July 21, 2026 10:49 AM
> To: Jan Kiszka <[email protected]>
> Cc: [email protected]; iwamatsu nobuhiro(岩松 信洋 □ＤＩＴＣ○
> ＣＰＴ) <[email protected]>
> Subject: [PATCH 6.1.y-cip] i3c: master: dw: stop hardcoding initial speed
> 
> From: Jack Chen <[email protected]>
> 
> commit 510d2358c466bf6588034f0d3b2266eed2bc0a51 upstream.
> 
> Bus-speed could be default(12.5MHz) or defined by users in dts.
> Dw-i3c-master should not hard-code the initial speed to be
> I3C_BUS_TYP_I3C_SCL_RATE (12.5MHz) And because of Synopsys's I3C
> controller limit (hcnt/lcnt register
> length) and core-clk provided, there is a limit to bus speed, too.
> For example, when core-clk is 250 MHz, the bus speed cannot be lowered
> below 1MHz.
> 
> Tested: tested with an i3c sensor and captured with a logic analyzer.
> 
> Signed-off-by: Jack Chen <[email protected]>
> Link:
> https://lore.kernel.org/r/[email protected]
> Signed-off-by: Alexandre Belloni <[email protected]>
> Signed-off-by: Nobuhiro Iwamatsu <[email protected]>
> ---
> 
> This fixes a build error in “drivers/i3c/master/dw-i3c-master.c” caused by a
> Renesas backport patch.
> 
> ```
>   CC      drivers/i3c/master/dw-i3c-master.o
> In file included from ./include/vdso/const.h:5,
>                  from ./include/linux/const.h:4,
>                  from ./include/linux/bits.h:5,
>                  from ./include/linux/bitops.h:6,
>                  from drivers/i3c/master/dw-i3c-master.c:8:
> drivers/i3c/master/dw-i3c-master.c: In function ‘dw_i3c_clk_cfg’:
> drivers/i3c/master/dw-i3c-master.c:534:40: error:
> ‘I3C_BUS_TYP_I3C_SCL_RATE’ undeclared (first use in this function); did
> you mean ‘I3C_BUS_SDR3_SCL_RATE’?
>   534 |         lcnt = DIV_ROUND_UP(core_rate,
> I3C_BUS_TYP_I3C_SCL_RATE) - hcnt;
>       |
> ^~~~~~~~~~~~~~~~~~~~~~~~
> ./include/uapi/linux/const.h:34:46: note: in definition of macro
> ‘__KERNEL_DIV_ROUND_UP’
>    34 | #define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
>       |                                              ^
> drivers/i3c/master/dw-i3c-master.c:534:16: note: in expansion of macro
> ‘DIV_ROUND_UP’
>   534 |         lcnt = DIV_ROUND_UP(core_rate,
> I3C_BUS_TYP_I3C_SCL_RATE) - hcnt;
>       |                ^~~~~~~~~~~~
> drivers/i3c/master/dw-i3c-master.c:534:40: note: each undeclared identifier is
> reported only once for each function it appears in
>   534 |         lcnt = DIV_ROUND_UP(core_rate,
> I3C_BUS_TYP_I3C_SCL_RATE) - hcnt;
>       |
> ^~~~~~~~~~~~~~~~~~~~~~~~
> ./include/uapi/linux/const.h:34:46: note: in definition of macro
> ‘__KERNEL_DIV_ROUND_UP’
>    34 | #define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
>       |                                              ^
> drivers/i3c/master/dw-i3c-master.c:534:16: note: in expansion of macro
> ‘DIV_ROUND_UP’
>   534 |         lcnt = DIV_ROUND_UP(core_rate,
> I3C_BUS_TYP_I3C_SCL_RATE) - hcnt;
>       |                ^~~~~~~~~~~~
> make[4]: *** [scripts/Makefile.build:250:
> drivers/i3c/master/dw-i3c-master.o] Error 1
> make[3]: *** [scripts/Makefile.build:503: drivers/i3c/master] Error 2
> make[2]: *** [scripts/Makefile.build:503: drivers/i3c] Error 2
> make[1]: *** [scripts/Makefile.build:503: drivers] Error 2
> make: *** [Makefile:2025: .] Error 2
> ```
> 
>  drivers/i3c/master/dw-i3c-master.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i3c/master/dw-i3c-master.c
> b/drivers/i3c/master/dw-i3c-master.c
> index d6585d0a20c50..8af2229df82ae 100644
> --- a/drivers/i3c/master/dw-i3c-master.c
> +++ b/drivers/i3c/master/dw-i3c-master.c
> @@ -531,7 +531,7 @@ static int dw_i3c_clk_cfg(struct dw_i3c_master
> *master)
>  	if (hcnt < SCL_I3C_TIMING_CNT_MIN)
>  		hcnt = SCL_I3C_TIMING_CNT_MIN;
> 
> -	lcnt = DIV_ROUND_UP(core_rate, I3C_BUS_TYP_I3C_SCL_RATE) -
> hcnt;
> +	lcnt = DIV_ROUND_UP(core_rate, master->base.bus.scl_rate.i3c) -
> hcnt;
>  	if (lcnt < SCL_I3C_TIMING_CNT_MIN)
>  		lcnt = SCL_I3C_TIMING_CNT_MIN;
> 
> @@ -541,7 +541,8 @@ static int dw_i3c_clk_cfg(struct dw_i3c_master
> *master)
>  	if (!(readl(master->regs + DEVICE_CTRL) &
> DEV_CTRL_I2C_SLAVE_PRESENT))
>  		writel(BUS_I3C_MST_FREE(lcnt), master->regs +
> BUS_FREE_TIMING);
> 
> -	lcnt = DIV_ROUND_UP(I3C_BUS_TLOW_OD_MIN_NS, core_period);
> +	lcnt = max_t(u8,
> +		     DIV_ROUND_UP(I3C_BUS_TLOW_OD_MIN_NS,
> core_period), lcnt);
>  	scl_timing = SCL_I3C_TIMING_HCNT(hcnt) |
> SCL_I3C_TIMING_LCNT(lcnt);
>  	writel(scl_timing, master->regs + SCL_I3C_OD_TIMING);
> 
> --
> 2.53.0