linux-kernel - Re: [PATCH 3/4] arm64: dts: ti: k3-am62-main: Add tidss clk-ctrl property

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Message-ID: <d7b874d5-a224-4e4c-a18b-6e68480b3349@bootlin.com>
Date: Mon, 11 Aug 2025 11:56:49 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Jyri Sarha <jyri.sarha@....fi>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Sam Ravnborg <sam@...nborg.org>,
 Benoit Parrot <bparrot@...com>, Lee Jones <lee@...nel.org>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Tero Kristo <kristo@...nel.org>, thomas.petazzoni@...tlin.com,
 Jyri Sarha <jsarha@...com>, Tomi Valkeinen <tomi.valkeinen@...com>,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 stable@...r.kernel.org
Subject: Re: [PATCH 3/4] arm64: dts: ti: k3-am62-main: Add tidss clk-ctrl
 property



Le 05/08/2025 à 08:44, Krzysztof Kozlowski a écrit :
> On Thu, Jul 31, 2025 at 11:50:16AM +0200, Louis Chauvet wrote:
>>
>>
>> Le 31/07/2025 à 02:17, Rob Herring a écrit :
>>> On Wed, Jul 30, 2025 at 07:02:46PM +0200, Louis Chauvet wrote:
>>>> For am62 processors, we need to use the newly created clk-ctrl property to
>>>> properly handle data edge sampling configuration. Add them in the main
>>>> device tree.
>>>>
>>>> Fixes: 32a1795f57ee ("drm/tidss: New driver for TI Keystone platform Display SubSystem")
>>>> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
>>>> ---
>>>>
>>>> Cc: stable@...r.kernel.org
>>>> ---
>>>>    arch/arm64/boot/dts/ti/k3-am62-main.dtsi | 6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/boot/dts/ti/k3-am62-main.dtsi b/arch/arm64/boot/dts/ti/k3-am62-main.dtsi
>>>> index 9e0b6eee9ac77d66869915b2d7bec3e2275c03ea..d3131e6da8e70fde035d3c44716f939e8167795a 100644
>>>> --- a/arch/arm64/boot/dts/ti/k3-am62-main.dtsi
>>>> +++ b/arch/arm64/boot/dts/ti/k3-am62-main.dtsi
>>>> @@ -76,6 +76,11 @@ audio_refclk1: clock-controller@...4 {
>>>>    			assigned-clock-parents = <&k3_clks 157 18>;
>>>>    			#clock-cells = <0>;
>>>>    		};
>>>> +
>>>> +		dss_clk_ctrl: dss_clk_ctrl@...0 {
>>>> +			compatible = "ti,am625-dss-clk-ctrl", "syscon";
>>>> +			reg = <0x8300 0x4>;
>>>
>>> H/w blocks are rarely only 4 bytes of registers... Does this belong to
>>> some larger block. The problem with bindings defining single registers
>>> like this is they don't get defined until needed and you have a constant
>>> stream of DT updates.
>>
>> In this case, I don't think there is a "larger block". This register exists
>> only because TI had issues in the display controller [1].
>>
>> Here is the extract of MMR registers ([2], page 4311):
>>
>> [...]
>> A2E4h AUDIO_REFCLK1_CTRL_PROXY <unrelated>
> 
> Here is clk ctrl proxy...

(Note: I linked and copied the wrong page in my previous mail, the page 
is 4309 and register addresses are 0x82e4 (audio_refclk1_ctrl), 0x8300 
(dpi0_clk_ctrl) and 0x8320 (dss_dispc_clksel1), but the issue remain the 
same)

The AUDIO_REFCLK1_CTRL is already defined in the simple-bus node, but 
with a size of 0x4 [1] and as a clock controller.

What is the correct solution in this case? Should I create a big syscon 
that overlap with audio_refclk0/1 range?

[1]:https://elixir.bootlin.com/linux/v6.16/source/arch/arm64/boot/dts/ti/k3-am62-main.dtsi#L73

>> A300h DPI0_CLK_CTRL_PROXY <this register, 32 bits>
> 
> and here as well, so pretty related. This looks also close to regular
> syscon and we do not define individual syscon registers as device nodes.

I agree this one can be included in the syscon device. Clock related 
registers starts at 0x8000 and ends at 0x8504, should I cover the whole 
range in the syscon?

I quickly looked at the other register, here is the repartition:

- 0x8000 - "normal" clock (divider + source selection)
- 0x8040 to 0x8298 - clock source selection
- 0x82e0 to 0x82e4 - clock control for audio (already implemented as 
clock driver)
- 0x8300 - the clock quirk (it seems that this is the only quirk 
register here)
- 0x8320 to 0x8500 - clock source selection

Thanks,
Louis Chauvet

> Best regards,
> Krzysztof
> 

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com