Re: [PATCH 2/2] arm64: dts: qcom: sm8450: Add IMEM and PIL info region

[Alex Elder]

On 2/14/23 6:34 AM, Mukesh Ojha wrote:
> +@alex,
>
> Please comment.
>
> -Mukesh
>
> On 2/7/2023 2:34 AM, Bjorn Andersson wrote:
> > On Mon, Feb 06, 2023 at 08:06:13PM +0530, Mukesh Ojha wrote:
> > > On 2/4/2023 3:07 AM, Konrad Dybcio wrote:
> > > > On 3.02.2023 18:04, Mukesh Ojha wrote:
> > > > > Add a simple-mfd representing IMEM on SM8450 and define the PIL
> > > > > relocation info region, so that post mortem tools will be able
> > > > > to locate the loaded remoteprocs.
> > > > >
> > > > > Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> > > > > ---
> > > >   From XBL:
> > > >
> > > > 0x14680000, 0x0002A000, "IMEM Base"
> > > >
> > > > Is there anything in that wider address range that would interest
> > > > us? I recall Alex once dug into that when diving into IPA, but
> > > > I can not recall the conclusion..

So you're saying a boot loader defines "IMEM Base" as
a range of memory, size 0x2a000.

> > > Spec-wise, yes IPA do own these 0x146A8000 - 0x146AA000 .
> > > But, not sure what they use it for.

And a subset of that range (at offset 0x28000, size 0x2000) is
set aside for use by IPA.  IPA *does* use this memory area as
"fast" memory to hold certain frequently-accessed tables.
Details of that are under the modem's control, and I don't
have knowledge of that.

The IPA driver currently maps it's portion of this memory,
but does *not* reflect that use in DT.  (This is something
that will be corrected at some point, possibly soon.)


> > The DT should not reflect the organization structure. Let's see if Alex
> > have any input on this.

As I understand it there's an "imem" node in DT defined, but
it just defines the range of memory, and is something referred
to by other drivers (or other nodes in a DTS file).  This seems
reasonable, and it kind of matches the view I've seen in
documents.  IPA does *not* follow that pattern, and should.

I don't really have any strong input either way.  I can help
define the "problem" but I don't claim to know the correct
way to represent this.

It's a contiguous block of special memory.  By convention
(design) its range divided up, with portions intended to be
used for different purposes, by different hardware.  IPA is
one of the users.

					-Alex


> > Thanks,
> > Bjorn
> >
> > > -Mukesh
> > > > Konrad
> > > > >    arch/arm64/boot/dts/qcom/sm8450.dtsi | 15 +++++++++++++++
> > > > >    1 file changed, 15 insertions(+)
> > > > >
> > > > > diff --git a/arch/arm64/boot/dts/qcom/sm8450.dtsi 
> > > > > b/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > > > index 5704750..474ea1b 100644
> > > > > --- a/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > > > +++ b/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > > > @@ -3536,6 +3536,21 @@
> > > > >                };
> > > > >            };
> > > > > +        sram@146aa000 {
> > > > > +            compatible = "qcom,sm8450-imem", "syscon", "simple-mfd";
> > > > > +            reg = <0 0x146aa000 0 0x1000>;
> > > > > +
> > > > > +            #address-cells = <1>;
> > > > > +            #size-cells = <1>;
> > > > > +
> > > > > +            ranges = <0 0 0x146aa000 0x1000>;
> > > > > +
> > > > > +            pil-reloc@94c {
> > > > > +                compatible = "qcom,pil-reloc-info";
> > > > > +                reg = <0x94c 0xc8>;
> > > > > +            };
> > > > > +        };
> > > > > +
> > > > >            apps_rsc: rsc@17a00000 {
> > > > >                label = "apps_rsc";
> > > > >                compatible = "qcom,rpmh-rsc";