linux-kernel - Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM

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Date: Fri, 19 Apr 2024 13:38:47 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Florian Fainelli <florian.fainelli@...adcom.com>
Cc: Elliot Berman <quic_eberman@...cinc.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Sebastian Reichel <sre@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
	Andy Yan <andy.yan@...k-chips.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
	Melody Olvera <quic_molvera@...cinc.com>,
	Shivendra Pratap <quic_spratap@...cinc.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM_RESET2

On Wed, Apr 17, 2024 at 10:50:07AM -0700, Florian Fainelli wrote:
> On 4/16/24 02:35, Sudeep Holla wrote:
> > On Sun, Apr 14, 2024 at 12:30:23PM -0700, Elliot Berman wrote:
> > > The PSCI SYSTEM_RESET2 call allows vendor firmware to define additional
> > > reset types which could be mapped to the reboot argument.
> > >
> > > Setting up reboot on Qualcomm devices can be inconsistent from chipset
> > > to chipset.
> >
> > That doesn't sound good. Do you mean PSCI SYSTEM_RESET doesn't work as
> > expected ? Does it mean it is not conformant to the specification ?
> >
> > > Generally, there is a PMIC register that gets written to
> > > decide the reboot type. There is also sometimes a cookie that can be
> > > written to indicate that the bootloader should behave differently than a
> > > regular boot. These knobs evolve over product generations and require
> > > more drivers. Qualcomm firmwares are beginning to expose vendor
> > > SYSTEM_RESET2 types to simplify driver requirements from Linux.
> > >
> >
> > Why can't this be fully userspace driven ? What is the need to keep the
> > cookie in the DT ?
> >
> >
>
> Using the second example in the Device Tree:
>
> mode-bootloader = <1 2>;
>
> are you suggesting that within psci_vendor_sys_reset2() we would look at the
> data argument and assume that we have something like this in memory:
>
> const char *cmd = data;
>
> cmd[] = "bootloader 2"
>
> where "bootloader" is the reboot command, and "2" is the cookie? From an
> util-linux, busybox, toybox, etc. we would have to concatenate those
> arguments with a space, but I suppose that would be doable.
>

Yes that was my thought when I wrote the email. But since I have looked at
existing bindings and support in the kernel in little more detail I would say.
So I am not sure what would be the better choice for PSCI SYSTEM_RESET2
especially when there is some ground support to build.

So I am open for alternatives including this approach.

--
Regards,
Sudeep