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

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Date: Wed, 17 Apr 2024 10:50:07 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Sudeep Holla <sudeep.holla@....com>,
 Elliot Berman <quic_eberman@...cinc.com>
Cc: 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, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 0/4] Implement vendor resets for PSCI SYSTEM_RESET2

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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