linux-kernel - Re: [PATCH v7 3/3] riscv: dts: thead: Add device tree VO clock controller

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Message-ID: <aBUCdA0ZSQL1n3i4@x1>
Date: Fri, 2 May 2025 10:35:48 -0700
From: Drew Fustini <drew@...7.com>
To: Michal Wilczynski <m.wilczynski@...sung.com>,
	Stephen Boyd <sboyd@...nel.org>
Cc: Stephen Boyd <sboyd@...nel.org>, mturquette@...libre.com,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	guoren@...nel.org, wefu@...hat.com, paul.walmsley@...ive.com,
	palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr,
	jszhang@...nel.org, p.zabel@...gutronix.de,
	m.szyprowski@...sung.com, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v7 3/3] riscv: dts: thead: Add device tree VO clock
 controller

On Wed, Apr 30, 2025 at 09:52:29AM +0200, Michal Wilczynski wrote:
> 
> 
> On 4/30/25 00:29, Stephen Boyd wrote:
> > Quoting Michal Wilczynski (2025-04-07 08:30:43)
> >> On 4/5/25 01:16, Drew Fustini wrote:
> >>>> diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
> >>>> index 527336417765..d4cba0713cab 100644
> >>>> --- a/arch/riscv/boot/dts/thead/th1520.dtsi
> >>>> +++ b/arch/riscv/boot/dts/thead/th1520.dtsi
> >>>> @@ -489,6 +489,13 @@ clk: clock-controller@...f010000 {
> >>>>                      #clock-cells = <1>;
> >>>>              };
> >>>>  
> >>>> +            clk_vo: clock-controller@...f528050 {
> >>>> +                    compatible = "thead,th1520-clk-vo";
> >>>> +                    reg = <0xff 0xef528050 0x0 0xfb0>;
> >>>
> >>> Thanks for your patch. It is great to have more of the clocks supported
> >>> upstream.
> >>>
> >>> The TH1520 System User Manual shows 0xFF_EF52_8000 for VO_SUBSYS on page
> >>> 205. Is there a reason you decided to use 0xFF_EF52_8050 as the base?
> >>>
> >>> I see on page 213 that the first register for VO_SUBSYS starts with
> >>> VOSYS_CLK_GATE at offset 0x50. I figure you did this to have the
> >>> CCU_GATE macros use offset of 0x0 instead 0x50.
> >>>
> >>> I kind of think the reg property using the actual base address
> >>> (0xFF_EF52_8000) makes more sense as that's a closer match to the tables
> >>> in the manual. But I don't have a strong preference if you think think
> >>> using 0xef528050 makes the CCU_GATE macros easier to read.
> >>
> >> Thank you for your comment.
> >>
> >> This was discussed some time ago. The main issue was that the address
> >> space was fragmented between clocks and resets. Initially, I proposed
> >> using syscon as a way to abstract this, but the idea wasn't particularly
> >> well received.
> >>
> >> So at the start of the 0xFF_EF52_8000 there is a reset register GPU_RST_CFG
> >> I need for resetting the GPU.
> >>
> >> For reference, here's the earlier discussion: [1]
> >>
> >> [1] - https://lore.kernel.org/all/1b05b11b2a8287c0ff4b6bdd079988c7.sboyd@kernel.org/
> >>
> > 
> > In that email I said you should have one node
> > clock-controller@...f528000. Why did 0x50 get added to the address?
> 
> Hi Stephen,
> In the v2 version of the patchset, there was no reset controller yet, so
> I thought your comment was made referring to that earlier version.
> This representation clearly describes the hardware correctly, which is
> the requirement for the Device Tree.
> 
> The manual, in section 5.4.1.6 VO_SUBSYS, describes the reset registers
> starting at 0xFF_EF52_8000:
> 
> GPU_RST_CFG             0x00
> DPU_RST_CFG             0x04
> MIPI_DSI0_RST_CFG       0x8
> MIPI_DSI1_RST_CFG       0xc
> HDMI_RST_CFG            0x14
> AXI4_VO_DW_AXI          0x18
> X2H_X4_VOSYS_DW_AXI_X2H 0x20
> 
> And the clock registers for VO_SUBSYS, manual section 4.4.1.6 start at offset 0x50:
> VOSYS_CLK_GATE          0x50
> VOSYS_CLK_GATE1         0x54
> VOSYS_DPU_CCLK_CFG0     0x64
> TEST_CLK_FREQ_STAT      0xc4
> TEST_CLK_CFG            0xc8
> 
> So I considered this back then and thought it was appropriate to divide
> it into two nodes, as the reset node wasn't being considered at that
> time.
> 
> When looking for the reference [1], I didn't notice if you corrected
> yourself later, but I do remember considering the single-node approach
> at the time.
> 
> > 
> 
> Best regards,
> -- 
> Michal Wilczynski <m.wilczynski@...sung.com>

I chatted with Stephen on irc about setting up a thead clk branch and
sending pull requests to Stephen.

Stephen - are there changes in this series that you want to see in order
to give your Reviewed-by?

Thanks,
Drew