linux-kernel - Re: [PATCH 0/3] soc: qcom: Add download mode support for QTI platforms

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Message-ID: <0178821e-a8cd-87c8-640c-4928201a3b5a@quicinc.com>
Date:   Thu, 12 Aug 2021 21:31:08 -0700
From:   Trilok Soni <quic_tsoni@...cinc.com>
To:     Stephen Boyd <swboyd@...omium.org>, Andy Gross <agross@...nel.org>,
        "Bjorn Andersson" <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Sai Prakash Ranjan" <saiprakash.ranjan@...eaurora.org>
CC:     <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        "Rajendra Nayak" <rnayak@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>, <quic_eberman@...cinc.com>
Subject: Re: [PATCH 0/3] soc: qcom: Add download mode support for QTI
 platforms

Stephen,

On 8/12/2021 5:16 PM, Stephen Boyd wrote:
> Quoting Sai Prakash Ranjan (2021-08-12 02:17:39)
>> Collecting ramdumps on QTI platforms mainly require two things,
>> SDI (System Debug Image) enabled firmware and kernel support to
>> configure download mode cookies and SDI settings. Ramdumps can
>> be collected once the system enters the download mode. To enter
>> download mode, magic values or cookies need to be set in IMEM
>> which is used by firmware to decide to enter download mode or not.
>> Download mode cookies remain the same across targets and SDI disable
>> register needs to be set or SDI needs to be disabled in case of normal
>> reboot since ramdumps are supposed to be for crash debugging and
>> not for every reboot. This series adds the kernel support required
>> to enter download mode.
> 
> I don't recall if we discussed this on the list, but I'd really prefer
> that we don't make kernel changes to support this beyond implementing
> PSCI SYSTEM_RESET2 support and then some sort of vendor specific (or if
> ARM is willing to update the spec then ARM specific) reset command on
> panic reboot paths. The idea is to set the cookie in the bootloader
> before the kernel is booted, then any insta-reboots/watchdogs would go
> into download mode, no special init code required to lay down the cookie
>>   create mode 100644 drivers/soc/qcom/download_mode.c

Some discussion by Elliot on the PSCI_SYSTEM_RESET2 and vendor bits was 
done here. You may want to check.

https://lkml.org/lkml/2020/2/24/1137

---Trilok Soni