Re: [PATCH v2 3/4] firmware: psci: Read and use vendor reset types

From: Konrad Dybcio <konrad.dybcio@linaro.org>
To: Elliot Berman <quic_eberman@quicinc.com>,
	Bjorn Andersson <andersson@kernel.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>
Cc: 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 3/4] firmware: psci: Read and use vendor reset types
Date: Mon, 15 Apr 2024 21:39:56 +0200	[thread overview]
Message-ID: <90b9da5e-8a2b-4a0d-bee8-bb21c74cb355@linaro.org> (raw)
In-Reply-To: <20240414-arm-psci-system_reset2-vendor-reboots-v2-3-da9a055a648f@quicinc.com>


On 4/14/24 21:30, 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.
> 
> 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@quicinc.com>
> ---

[...]

> +arch_initcall(psci_init_system_reset2_modes);

Perhaps this could be called from \/

Konrad

> +
>   int __init psci_dt_init(void)
>   {
>   	struct device_node *np;
>