Re: [PATCH RFC 5/6] riscv: dts: thead: Add PVT node

[Drew Fustini <drew@pdp7.com>]

On Mon, Jun 09, 2025 at 08:49:57PM +0200, Michal Wilczynski wrote:
> 
> 
> On 6/1/25 19:32, Drew Fustini wrote:
> > On Sun, Jun 01, 2025 at 09:50:52AM +0200, Michal Wilczynski wrote:
> >>
> >>
> >> On 5/27/25 10:00, Drew Fustini wrote:
> >>> On Sat, May 24, 2025 at 11:14:59PM +0200, Michal Wilczynski wrote:
> >>>> Add PVT DT node for thermal sensor.
> >>>>
> >>>> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
> >>>> ---
> >>>>  arch/riscv/boot/dts/thead/th1520.dtsi | 11 +++++++++++
> >>>>  1 file changed, 11 insertions(+)
> >>>>
> >>>> diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
> >>>> index f24e12d7259fabcfbdc2dfa966d759db06684ab4..faf5c3aaf209b24cd99ddc377a88e08a8cce24fe 100644
> >>>> --- a/arch/riscv/boot/dts/thead/th1520.dtsi
> >>>> +++ b/arch/riscv/boot/dts/thead/th1520.dtsi
> >>>> @@ -648,6 +648,17 @@ padctrl_aosys: pinctrl@fffff4a000 {
> >>>>  			thead,pad-group = <1>;
> >>>>  		};
> >>>>  
> >>>> +		pvt: pvt@fffff4e000 {
> >>>> +			compatible = "moortec,mr75203";
> >>>> +			reg = <0xff 0xfff4e000 0x0 0x80>,
> >>>> +			      <0xff 0xfff4e080 0x0 0x100>,
> >>>> +			      <0xff 0xfff4e180 0x0 0x680>,
> >>>> +			      <0xff 0xfff4e800 0x0 0x600>;
> >>>> +			reg-names = "common", "ts", "pd", "vm";
> >>>> +			clocks = <&aonsys_clk>;
> >>>> +			#thermal-sensor-cells = <1>;
> >>>> +		};
> >>>> +
> >>>>  		gpio@fffff52000 {
> >>>>  			compatible = "snps,dw-apb-gpio";
> >>>>  			reg = <0xff 0xfff52000 0x0 0x1000>;
> >>>>
> >>>> -- 
> >>>> 2.34.1
> >>>>
> >>>
> >>> I found that on my lpi4a that boot while hang after applying this patch.
> >>> I think that it is related to clocks as boot finished okay when using
> >>> clk_ignore_unused on the kernel cmdline. Do you happen have that in your
> >>> kernel cmdline?
> >>>
> >>> I need to investigate further to understand which clocks are causing the
> >>> problem.
> >>>
> >>> Thanks,
> >>> Drew
> >>>
> >>
> >> Thanks for your earlier message. I've investigated, and you were right
> >> about the clocks – the specific one causing the hang is CLK_CPU2AON_X2H.
> > 
> > Thanks for tracking down the clk causing the hang. I can confirm that
> > this fixes the boot hang:
> > 
> > diff --git a/drivers/clk/thead/clk-th1520-ap.c b/drivers/clk/thead/clk-th1520-ap.c
> > index ebfb1d59401d..4d0179b8c17c 100644
> > --- a/drivers/clk/thead/clk-th1520-ap.c
> > +++ b/drivers/clk/thead/clk-th1520-ap.c
> > @@ -792,7 +792,7 @@ static CCU_GATE(CLK_AON2CPU_A2X, aon2cpu_a2x_clk, "aon2cpu-a2x", axi4_cpusys2_ac
> >                 0x134, BIT(8), 0);
> >  static CCU_GATE(CLK_X2X_CPUSYS, x2x_cpusys_clk, "x2x-cpusys", axi4_cpusys2_aclk_pd,
> >                 0x134, BIT(7), 0);
> > -static CCU_GATE(CLK_CPU2AON_X2H, cpu2aon_x2h_clk, "cpu2aon-x2h", axi_aclk_pd, 0x138, BIT(8), 0);
> > +static CCU_GATE(CLK_CPU2AON_X2H, cpu2aon_x2h_clk, "cpu2aon-x2h", axi_aclk_pd, 0x138, BIT(8), CLK_IGNORE_UNUSED);
> >  static CCU_GATE(CLK_CPU2PERI_X2H, cpu2peri_x2h_clk, "cpu2peri-x2h", axi4_cpusys2_aclk_pd,
> >                 0x140, BIT(9), CLK_IGNORE_UNUSED);
> >  static CCU_GATE(CLK_PERISYS_APB1_HCLK, perisys_apb1_hclk, "perisys-apb1-hclk", perisys_ahb_hclk_pd,
> > 
> >>
> >> This appears to be an AHB bus clock required for CPU access to the AON
> >> domain. My proposed solution is to make the pvt node a child of a new
> >> parent bus node in the Device Tree. This new "AON bus" node would then
> >> explicitly request and manage CLK_CPU2AON_X2H, ensuring it's enabled
> >> when its children are accessed.
> >>
> >> What are your thoughts on this approach?
> > 
> > I think that is a good approach. The alternative would be to just add
> > CLK_IGNORE_UNUSED like above. I've done it before but it is a bit of a
> > hack.
> 
> I've followed up on the idea of creating a parent bus node. My attempt
> using simple-pm-bus ran into a couple of significant issues that suggest
> it's not the correct path.
> 
> First, the TRM doesn't seem to specify an address range for this bus.
> The range I used in my test was only for the PVT controller itself,
> which would be an incorrect abstraction in the device tree.
> 
> Second, simple-pm-bus requires its child nodes to use the PM runtime API
> (pm_runtime_resume_and_get, etc.). Forcing this on consumer drivers like
> the PVT sensor seems like an inappropriate dependency.
> 
> Additionally, I discovered that the PWM driver has a similar problem,
> silently failing because another clock, CLK_PERISYS_APB1_HCLK, is not
> enabled.
> 
> The most correct solution likely involves refactoring the clock parent
> relationships in clk-th1520-ap.c. However, as a more immediate and less
> invasive fix, I propose we apply the CLK_IGNORE_UNUSED flag for both
> CLK_CPU2AON_X2H and CLK_PERISYS_APB1_HCLK in the v2 patch. This will fix
> the boot hang and the PWM issue while we consider the larger clock
> driver changes separately.
> 
> Does that sound like a reasonable plan for the v2 series?

Yes, I think that sounds like a good plan. I am okay with adding
CLK_IGNORE_UNUSED for CLK_CPU2AON_X2H and CLK_PERISYS_APB1_HCLK until a
better solution is found.

I like the idea of revisting the parent relationships in the driver. I
added CLK_IGNORE_UNUSED to several clocks in order to fix boot hangs
when I removed clk_ignore_unused from the kernel cmdline. However, I
don't think that I addressed the root cause.

Thanks,
Drew
.