linux-kernel - Re: [PATCH v6 4/6] clk: spacemit: k1: Add TWSI8 bus and function clocks

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Message-ID: <89385654-11bc-4cf0-b94e-15bf841ac215@riscstar.com>
Date: Tue, 8 Apr 2025 14:37:29 -0500
From: Alex Elder <elder@...cstar.com>
To: Haylen Chu <heylenay@....org>, Michael Turquette
 <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Haylen Chu <heylenay@...look.com>,
 Yixun Lan <dlan@...too.org>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>
Cc: linux-riscv@...ts.infradead.org, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 spacemit@...ts.linux.dev, Inochi Amaoto <inochiama@...look.com>,
 Chen Wang <unicornxdotw@...mail.com>, Jisheng Zhang <jszhang@...nel.org>,
 Meng Zhang <zhangmeng.kevin@...ux.spacemit.com>
Subject: Re: [PATCH v6 4/6] clk: spacemit: k1: Add TWSI8 bus and function
 clocks

On 4/1/25 12:24 PM, Haylen Chu wrote:
> The control register for TWSI8 clocks, APBC_TWSI8_CLK_RST, contains mux
> selection bits, reset assertion bit and enable bits for function and bus
> clocks. It has a quirk that reading always results in zero.
> 
> As a workaround, let's hardcode the mux value as zero to select
> pll1_d78_31p5 as parent and treat twsi8_clk as a gate, whose enable mask
> is combined from the real bus and function clocks to avoid the
> write-only register being shared between two clk_hws, in which case
> updates of one clk_hw zero the other's bits.
> 
> With a 1:1 factor serving as placeholder for the bus clock, the I2C-8
> controller could be brought up, which is essential for boards attaching
> power-management chips to it.
> 
> Signed-off-by: Haylen Chu <heylenay@....org>

Now that I understand why, I'm glad you put this into a separate
patch.  However I think you should make a note in the code to
indicate there's something different about this one clock.
People can then go back (with "git blame") to see the explanation
above.

Please consider adding such a comment in your next version.

Reviewed-by: Alex Elder <elder@...cstar.com>

> ---
>   drivers/clk/spacemit/ccu-k1.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/clk/spacemit/ccu-k1.c b/drivers/clk/spacemit/ccu-k1.c
> index cd95c4f9c127..5804c2f85407 100644
> --- a/drivers/clk/spacemit/ccu-k1.c
> +++ b/drivers/clk/spacemit/ccu-k1.c
> @@ -397,6 +397,8 @@ CCU_MUX_GATE_DEFINE(twsi6_clk, twsi_parents, APBC_TWSI6_CLK_RST, 4, 3, BIT(1),
>   		    0);
>   CCU_MUX_GATE_DEFINE(twsi7_clk, twsi_parents, APBC_TWSI7_CLK_RST, 4, 3, BIT(1),
>   		    0);
> +CCU_GATE_DEFINE(twsi8_clk, CCU_PARENT_HW(pll1_d78_31p5), APBC_TWSI8_CLK_RST,
> +		BIT(1) | BIT(0), 0);
>   
>   static const struct clk_parent_data timer_parents[] = {
>   	CCU_PARENT_HW(pll1_d192_12p8),
> @@ -528,6 +530,7 @@ CCU_GATE_DEFINE(twsi6_bus_clk, CCU_PARENT_HW(apb_clk), APBC_TWSI6_CLK_RST,
>   		BIT(0), 0);
>   CCU_GATE_DEFINE(twsi7_bus_clk, CCU_PARENT_HW(apb_clk), APBC_TWSI7_CLK_RST,
>   		BIT(0), 0);
> +CCU_FACTOR_DEFINE(twsi8_bus_clk, CCU_PARENT_HW(apb_clk), 1, 1);
>   
>   CCU_GATE_DEFINE(timers1_bus_clk, CCU_PARENT_HW(apb_clk), APBC_TIMERS1_CLK_RST,
>   		BIT(0), 0);
> @@ -1059,6 +1062,7 @@ static struct clk_hw *k1_ccu_apbc_hws[] = {
>   	[CLK_TWSI5]		= &twsi5_clk.common.hw,
>   	[CLK_TWSI6]		= &twsi6_clk.common.hw,
>   	[CLK_TWSI7]		= &twsi7_clk.common.hw,
> +	[CLK_TWSI8]		= &twsi8_clk.common.hw,
>   	[CLK_TIMERS1]		= &timers1_clk.common.hw,
>   	[CLK_TIMERS2]		= &timers2_clk.common.hw,
>   	[CLK_AIB]		= &aib_clk.common.hw,
> @@ -1110,6 +1114,7 @@ static struct clk_hw *k1_ccu_apbc_hws[] = {
>   	[CLK_TWSI5_BUS]		= &twsi5_bus_clk.common.hw,
>   	[CLK_TWSI6_BUS]		= &twsi6_bus_clk.common.hw,
>   	[CLK_TWSI7_BUS]		= &twsi7_bus_clk.common.hw,
> +	[CLK_TWSI8_BUS]		= &twsi8_bus_clk.common.hw,
>   	[CLK_TIMERS1_BUS]	= &timers1_bus_clk.common.hw,
>   	[CLK_TIMERS2_BUS]	= &timers2_bus_clk.common.hw,
>   	[CLK_AIB_BUS]		= &aib_bus_clk.common.hw,