linux-kernel - Re: [PATCH 1/3] arm64: dts: qcom: sm8450: Add qfprom node

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Date: Sun, 17 Mar 2024 20:21:58 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Mukesh Ojha <quic_mojha@...cinc.com>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>, robh@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, linux-arm-msm@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] arm64: dts: qcom: sm8450: Add qfprom node

On Thu, Mar 14, 2024 at 10:13:59PM +0530, Mukesh Ojha wrote:
> Sorry for the late reply, was on vacation.
> 
> On 3/6/2024 9:24 PM, Konrad Dybcio wrote:
> > 
> > 
> > On 3/6/24 13:26, Mukesh Ojha wrote:
> > > Add the qfprom node for sm8450 SoC.
> > > 
> > > Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> > > ---
> > >   arch/arm64/boot/dts/qcom/sm8450.dtsi | 7 +++++++
> > >   1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > b/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > index b86be34a912b..02089a388d03 100644
> > > --- a/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > +++ b/arch/arm64/boot/dts/qcom/sm8450.dtsi
> > > @@ -4575,6 +4575,13 @@
> > >               };
> > >           };
> > > +        qfprom: efuse@...c8000 {
> > > +            compatible = "qcom,sm8450-qfprom", "qcom,qfprom";
> > > +            reg = <0 0x221c8000 0 0x1000>;
> > 
> > Is is really only 0x1000-long? Also, is the base you put
> > here the ECC-corrected part (if that still exists)?
> 
> No, its not.
> 
> Entire fuse space is this.
> 0x221C0000-0x221Cbfff
> 
> ECC corrected range is this 0x221C2000-0x221C3fff and High level OS

That's 0x2000. Does this then also imply that the ECC-corrected values
are no longer mapped 1:1 with non-corrected, or why do they differ in
size?

> does have a access to ECC range however, they are not recommended for
> SW usage.
> 
> Above mentioned SW range(4) in the patch is  one and only accessible range
> available out of 0-7 SW ranges(0x221C4000-0x221Cbfff with each
> size 0x1000) and does not have ECC fuses.
> 

So you're saying that in contrast to other platforms, the 4th software
range, dedicated for HLOS, does not have a matching ECC-corrected
shadow? If that's the case, then "not recommended for SW usage" sounds
wrong.

> All the downstream use cases are getting fulfilled with this.
> 

You only need ECC if you're unlucky...

Regards,
Bjorn