Message-ID: <88bd0152-8b53-5ae2-bb16-5060419ca580@linaro.org>
Date:   Wed, 8 Mar 2023 21:50:21 +0100
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Subject: Re: [RFC PATCH 3/6] soc: qcom: Add Qualcomm minidump kernel driver
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To:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Mukesh Ojha <quic_mojha@quicinc.com>, agross@kernel.org,
        andersson@kernel.org, keescook@chromium.org, tony.luck@intel.com,
        gpiccoli@igalia.com, catalin.marinas@arm.com, will@kernel.org
Cc:     linux-arm-msm@vger.kernel.org, linux-remoteproc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
References: <1676978713-7394-1-git-send-email-quic_mojha@quicinc.com>
 <1676978713-7394-4-git-send-email-quic_mojha@quicinc.com>
 <00b37174-f19e-ce59-b520-304891f6e2ef@linaro.org>
From:   Konrad Dybcio <konrad.dybcio@linaro.org>
In-Reply-To: <00b37174-f19e-ce59-b520-304891f6e2ef@linaro.org>
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On 8.03.2023 21:22, Srinivas Kandagatla wrote:
> 
> 
> On 21/02/2023 11:25, Mukesh Ojha wrote:
>> Minidump is a best effort mechanism to collect useful and predefined
>> data for first level of debugging on end user devices running on
>> Qualcomm SoCs. It is built on the premise that System on Chip (SoC)
>> or subsystem part of SoC crashes, due to a range of hardware and
>> software bugs. Hence, the ability to collect accurate data is only
>> a best-effort. The data collected could be invalid or corrupted,
>> data collection itself could fail, and so on.
>>
>> Qualcomm devices in engineering mode provides a mechanism for
>> generating full system ramdumps for post mortem debugging. But in some
>> cases it's however not feasible to capture the entire content of RAM.
>> The minidump mechanism provides the means for selecting region should
>> be included in the ramdump. The solution supports extracting the
>> ramdump/minidump produced either over USB or stored to an attached
>> storage device.
>>
>> The core of minidump feature is part of Qualcomm's boot firmware code.
>> It initializes shared memory(SMEM), which is a part of DDR and
>> allocates a small section of it to minidump table i.e also called
>> global table of content (G-ToC). Each subsystem (APSS, ADSP, ...) has
>> their own table of segments to be included in the minidump, all
>> references from a descriptor in SMEM (G-ToC). Each segment/region has
>> some details like name, physical address and it's size etc. and it
>> could be anywhere scattered in the DDR.
>>
>> Minidump kernel driver adds the capability to add linux region to be
>> dumped as part of ram dump collection. It provides appropriate symbol
>> to check its enablement and register client regions.
>>
>> To simplify post mortem debugging, it creates and maintain an ELF
>> header as first region that gets updated with upon registration
>> of a new region.
>>
>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>> ---
[...]

>> +int qcom_minidump_ready(void)
>> +{
>> +    void *ptr;
>> +    struct device_node *np;
>> +    static bool is_smem_available = true;
>> +
>> +    if (!is_smem_available || !(np = of_find_compatible_node(NULL, NULL, "qcom,smem"))) {
> 
> just check for dt node here does not mean that smem device is available, you should probably check if the device is avaliable aswell using of_device_is_available()
> 
> 
> We should proabably return -EPROBEDEFER incase the node is present and device is not present.
qcom_smem_get() seems to handle -EPROBE_DEFER internally, so this check
may be entirely redundant.

Konrad