linux-kernel - Re: [PATCH v3 3/4] firmware: psci: Read and use vendor reset types

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Date: Tue, 21 May 2024 12:06:17 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Elliot Berman <quic_eberman@...cinc.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>
Cc: 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 v3 3/4] firmware: psci: Read and use vendor reset types

On 5/15/24 16:09, Elliot Berman wrote:
> SoC vendors have different types of resets and are controlled through
> various registers. For instance, Qualcomm chipsets can reboot to a
> "download mode" that allows a RAM dump to be collected. Another example
> is they also support writing a cookie that can be read by bootloader
> during next boot. PSCI offers a mechanism, SYSTEM_RESET2, for these
> vendor reset types to be implemented without requiring drivers for every
> register/cookie.
> 
> Add support in PSCI to statically map reboot mode commands from
> userspace to a vendor reset and cookie value using the device tree.
> 
> A separate initcall is needed to parse the devicetree, instead of using
> psci_dt_init because mm isn't sufficiently set up to allocate memory.
> 
> Reboot mode framework is close but doesn't quite fit with the
> design and requirements for PSCI SYSTEM_RESET2. Some of these issues can
> be solved but doesn't seem reasonable in sum:
>   1. reboot mode registers against the reboot_notifier_list, which is too
>      early to call SYSTEM_RESET2. PSCI would need to remember the reset
>      type from the reboot-mode framework callback and use it
>      psci_sys_reset.
>   2. reboot mode assumes only one cookie/parameter is described in the
>      device tree. SYSTEM_RESET2 uses 2: one for the type and one for
>      cookie.
>   3. psci cpuidle driver already registers a driver against the
>      arm,psci-1.0 compatible. Refactoring would be needed to have both a
>      cpuidle and reboot-mode driver.
> 
> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>

Tested-by: Florian Fainelli <florian.fainelli@...adcom.com>

Thanks!
-- 
Florian


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