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

[Haylen Chu <heylenay@4d2.org>]

On Tue, Apr 08, 2025 at 02:37:29PM -0500, Alex Elder wrote:
> 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@4d2.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.

Sure I'm willing to.

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

Best regards,
Haylen Chu

> > ---
> >   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,
>