linux-kernel - Re: [PATCH 02/11] nvmem: qfprom: Mark core clk as optional

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Message-Id: <CV5YJVXIL8OT.1ZWW3KVCHPTA5@otso>
Date:   Wed, 30 Aug 2023 16:43:53 +0200
From:   "Luca Weiss" <luca.weiss@...rphone.com>
To:     "Doug Anderson" <dianders@...omium.org>
Cc:     <cros-qcom-dts-watchers@...omium.org>,
        "Andy Gross" <agross@...nel.org>,
        "Bjorn Andersson" <andersson@...nel.org>,
        "Konrad Dybcio" <konrad.dybcio@...aro.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        "Conor Dooley" <conor+dt@...nel.org>,
        "Srinivas Kandagatla" <srinivas.kandagatla@...aro.org>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Viresh Kumar" <viresh.kumar@...aro.org>,
        <~postmarketos/upstreaming@...ts.sr.ht>,
        <phone-devel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-gpio@...r.kernel.org>, <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 02/11] nvmem: qfprom: Mark core clk as optional

On Wed Aug 30, 2023 at 4:30 PM CEST, Doug Anderson wrote:
> Hi,
>
> On Wed, Aug 30, 2023 at 2:58 AM Luca Weiss <luca.weiss@...rphone.com> wrote:
> >
> > On some platforms like sc7280 on non-ChromeOS devices the core clock
> > cannot be touched by Linux so we cannot provide it. Mark it as optional
> > as accessing qfprom works without it.
> >
> > Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
> > ---
> >  drivers/nvmem/qfprom.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Are you actually testing burning fuses from the OS, or are you just
> using the nvmem in "read-only" mode? From comments in the bindings, if
> you're trying to burn the fuses then the clock is required. If things
> are in read-only mode then the clock isn't required.

Hi Doug,

I definitely don't plan on burning any fuses on this phone. Not even
sure that's allowed by the TZ / boot stack.

>
> When I compare to the driver, it seems like the driver assumes that if
> more than one memory region is provided then you must be supporting
> burning fuses. The bindings agree that having 4 memory regions
> specified means that the nvmem supports burning and 1 memory region
> specified means read-only. The extra 3 memory regions in the nvmem are
> all about fuse burning, I believe.
>
> So maybe the right fix here is to just change your dts to specify one
> memory region?

I got feedback from Konrad that this here would be the preferred
approach compared to having a different dts for ChromeOS vs non-ChromeOS
devices. I don't feel strongly to either, for me it's also okay to
remove the extra memory regions and only have the main one used on
regular qcom devices.

Let me know what you think.

Regards
Luca

>
> -Doug