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

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Date: Wed, 1 May 2024 19:21:16 -0700
From: Elliot Berman <quic_eberman@...cinc.com>
To: Sudeep Holla <sudeep.holla@....com>
CC: Florian Fainelli <florian.fainelli@...adcom.com>,
        Bjorn Andersson
	<andersson@...nel.org>,
        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>
Subject: Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM_RESET2

On Fri, Apr 19, 2024 at 01:38:47PM +0100, Sudeep Holla wrote:
> 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.

If we can't go with the DT approach, my preference would be to go with a
bootconfig and sysfs for controlling the mappings, although I don't
think userspace need/should control the mappings of cmd -> cookies.

I wanted to check if you are okay with proceeding with the reboot-mode
DT bindings approach unless we have some other better standard? If yes,
do you have any preference based on Konrad's comment [1]? I can send out
v3 with the couple comments from Dmitry and Krzysztof's addressed.

Thanks,
Elliot

[1]: https://lore.kernel.org/all/20240419123847.ica22nft3sejqnm7@bogus/