Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM_RESET2

From: Florian Fainelli <florian.fainelli@broadcom.com>
To: Sudeep Holla <sudeep.holla@arm.com>,
	Elliot Berman <quic_eberman@quicinc.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, linux-pm@vger.kernel.org,
	linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM_RESET2
Date: Wed, 17 Apr 2024 10:50:07 -0700	[thread overview]
Message-ID: <48f366f5-4a17-474c-a8e3-6d79c9092d62@broadcom.com> (raw)
In-Reply-To: <Zh5GWqt2oCNHdF_h@bogus>

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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.

For the use cases that I am after we did not have a need for the cookie, 
so I admit I did not think too much about it.
-- 
Florian

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