Re: [PATCH] arm64: dts: imx8mm: Add NOC node

[Tommaso Merciai <tomm.merciai@gmail.com>]

On Wed, Nov 03, 2021 at 08:19:34AM -0500, Adam Ford wrote:
> On Wed, Nov 3, 2021 at 7:43 AM Tommaso Merciai <tomm.merciai@gmail.com> wrote:
> >
> > Add support for dynamic frequency scaling of the main NOC configuration
> > on imx8mm.
> >
> > References:
> >  - i.MX 8M Mini Applications Processor RM, Rev. 3, 11/2020
> >  - f18e6d573b80 arm64: dts: imx8mq: Add NOC node
> >  - 912b9dacf3f0 arm64: dts: imx8mq: increase NOC clock to 800 MHz
> > ---
> 
> + Abel
> 
> >  arch/arm64/boot/dts/freescale/imx8mm.dtsi | 25 +++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/freescale/imx8mm.dtsi b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > index c2f3f118f82e..c5f64abcecff 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > @@ -719,6 +719,31 @@ pgc_mipi: power-domain@11 {
> >                         };
> >                 };
> >
> > +               noc: interconnect@32700000 {
> > +                       compatible = "fsl,imx8mm-noc", "fsl,imx8m-noc";
> > +                       reg = <0x32700000 0x100000>;
> > +                       clocks = <&clk IMX8MM_CLK_NOC>;
> > +                       fsl,ddrc = <&ddrc>;
> > +                       #interconnect-cells = <1>;
> > +                       operating-points-v2 = <&noc_opp_table>;
> > +
> > +                       noc_opp_table: opp-table {
> > +                               compatible = "operating-points-v2";
> > +
> > +                               opp-133M {
> > +                                       opp-hz = /bits/ 64 <133333333>;
> > +                               };
> > +
> > +                               opp-400M {
> > +                                       opp-hz = /bits/ 64 <400000000>;
> > +                               };
> > +
> > +                               opp-800M {
> > +                                       opp-hz = /bits/ 64 <800000000>;
> > +                               };
> 
> When I look at the opp table from the NXP's custom kernel [1] , they
> have a different opp table with a max frequency of 750MHz instead of
> 800MHz.  The i.MX8MM Ref manual shows there is something at 3270_0000,
> but it doesn't go into details of the registers there. However the max
> speed of the NOC clock does appear to be 800MHz and not the 750 MHz
> listed in the NXP kernel.
> 
> However, In the clk node of imx8mm.dtsi file, the IMX8MM_CLK_NOC
> parent is set to IMX8MM_SYS_PLL3_OUT and IMX8MM_SYS_PLL3_OUT is set to
> 750MHz, so I think setting the IMX8MM_CLK_NOC to 800MHz is likely not
> what we want if we're setting this clock parent and clock rate to
> 750MHz.  However if the NOC operates correctly at 800MHz when the
> parent is set to IMX8MM_SYS_PLL1_800M, it might make sense.  Looking
> at the imx8mq.dtsi file, it appears that the NOC node is referencing
> the ddrc node, and the imx8mq is able to operate the ddrc at 800MHz,
> while I beleive the 8MM is capped at 750M.
> 
> Since I do not know if the NOC is tied to the processor speed, the
> DRAM speed, or it runs independently, I can't say with any confidence
> what it should be and/or how to test it, but I would assume that with
> the ddrc node capped at 750MHz, the opp table in the NXP kernel is
> probably the correct one.
> 
> [1] - https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mm.dtsi?h=lf-5.10.y
> 
> adam
  
  Hi Adam,
  Thanks for your review.

  Tommaso

> 
> > +                       };
> > +               };
> > +
> >                 aips2: bus@30400000 {
> >                         compatible = "fsl,aips-bus", "simple-bus";
> >                         reg = <0x30400000 0x400000>;
> > --
> > 2.25.1
> >