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

[Louis Chauvet]

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@xxxxxxxxxxx>
> > > > ---
> > > >
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > ---
> > > >    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@82e4 {
> > > >    			assigned-clock-parents = <&k3_clks 157 18>;
> > > >    			#clock-cells = <0>;
> > > >    		};
> > > > +
> > > > +		dss_clk_ctrl: dss_clk_ctrl@8300 {
> > > > +			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