Received-SPF: pass (google.com: domain of linux-kernel+bounces-152018-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Date: Fri, 19 Apr 2024 16:31:17 -0700
From: Elliot Berman <quic_eberman@quicinc.com>
To: Sudeep Holla <sudeep.holla@arm.com>
CC: Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio
	<konrad.dybcio@linaro.org>,
        Sebastian Reichel <sre@kernel.org>, Rob Herring
	<robh@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>, Vinod Koul <vkoul@kernel.org>,
        Andy Yan
	<andy.yan@rock-chips.com>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        "Mark
 Rutland" <mark.rutland@arm.com>,
        Bartosz Golaszewski
	<bartosz.golaszewski@linaro.org>,
        Satya Durga Srinivasu Prabhala
	<quic_satyap@quicinc.com>,
        Melody Olvera <quic_molvera@quicinc.com>,
        Shivendra Pratap <quic_spratap@quicinc.com>,
        <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        Florian Fainelli <florian.fainelli@broadcom.com>,
        <linux-pm@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>
Subject: Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM_RESET2
Message-ID: <20240419134542691-0700.eberman@hu-eberman-lv.qualcomm.com>
References: <20240414-arm-psci-system_reset2-vendor-reboots-v2-0-da9a055a648f@quicinc.com>
 <Zh5GWqt2oCNHdF_h@bogus>
 <20240417140957985-0700.eberman@hu-eberman-lv.qualcomm.com>
 <20240419085345.4ovebbbmcabo3f73@bogus>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20240419085345.4ovebbbmcabo3f73@bogus>

On Fri, Apr 19, 2024 at 09:53:45AM +0100, Sudeep Holla wrote:
> On Wed, Apr 17, 2024 at 02:54:41PM -0700, Elliot Berman wrote:
> > On Tue, Apr 16, 2024 at 10:35:22AM +0100, 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 ?
> > >
> >
> > I was motivating the reason for using SYSTEM_RESET2. How to set the PMIC
> > register and IMEM cookie can change between chipsets. Using
> > SYSTEM_RESET2 alows us to abstract how to perform the reset.
> 
> Fair enough. But I assume you are not providing the details of PMIC register
> or IMEM cookie via DT.

Kernel doesn't need this info.

> 
> Anyways you did confirm if PSCI SYSTEM_RESET works as expected or not. That
> is default and must work.
> 

Yes, SYSTEM_RESET works on Quacomm firmware. The bindings disallow
trying to override the default reboot. (reboot command = NULL or "") The
PSCI parsing of the DT also doesn't have any of the special handling to
deal with "mode-normal".

> > > > 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 ?
> >
> > As Dmitry pointed out, this information isn't discoverable. I suppose
> > we could technically use bootconfig or kernel command-line to convey the
> > map although I think devicetree is the right spot for this mapping.
> >
> 
> Yes and as usual DT has become dumping ground for firmware that don't
> make things discoverable. Make crap that Qcom puts in the DT are firmware
> related and can be make discoverable. Anyways it is sad that no efforts
> to make it so are done as DT is always there to provide shortcuts.
> 
> > - Other vendor-specific bits for PSCI are described in the devicetree.
> >   One example is the suspend param (e.g. the StateID) for cpu idle
> >   states.
> 
> You are right, but that is the only example I can see and it was done
> in very early days of PSCI. It shouldn't be example if there are better
> ways.
> 
> > - Describing firmware bits in the DT isn't unprecedented, and putting
> >   this information outside the DT means that other OSes (besides Linux)
> >   need their own way to convey this information.
> 
> Correct but it can be Qcom specific firmware interface. There are so many
> already. This splitting information between firmware and DT works well
> for vertically integrated things which probably is the case with most of
> Qcom SoCs but it is prone to issues if DT and firmware mismatch. Firmware
> discovery eliminates such issues.
> 

I worry about designing interfaces both in Qualcomm firmware and in
the PSCI driver which doesn't really suit handling the discovery. We can
implement the dynamic discovery mechanims once there is a board which
needs it.

Thanks,
Elliot