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Subject: Re: [PATCH 0/3] soc: qcom: Add download mode support for QTI
 platforms
To:     Stephen Boyd <swboyd@chromium.org>, Andy Gross <agross@kernel.org>,
        "Bjorn Andersson" <bjorn.andersson@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        "Sai Prakash Ranjan" <saiprakash.ranjan@codeaurora.org>
CC:     <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
        "Rajendra Nayak" <rnayak@codeaurora.org>,
        Sibi Sankar <sibis@codeaurora.org>, <quic_eberman@quicinc.com>
References: <cover.1628757036.git.saiprakash.ranjan@codeaurora.org>
 <CAE-0n52PzadMxB_4h2DGJGLO++Bu_PCSsxS8NHe+cuhv=Mw0sA@mail.gmail.com>
From:   Trilok Soni <quic_tsoni@quicinc.com>
Message-ID: <0178821e-a8cd-87c8-640c-4928201a3b5a@quicinc.com>
Date:   Thu, 12 Aug 2021 21:31:08 -0700
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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