linux-hardening - Re: [PATCH 0/4] Retrieve information about DDR from SMEM

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Message-ID: <e7bd2840-dd93-40dd-a1bc-4cd606a34b44@oss.qualcomm.com>
Date: Fri, 11 Apr 2025 11:48:55 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>, Kees Cook <kees@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Dmitry Baryshkov <lumag@...nel.org>
Cc: Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-hardening@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 0/4] Retrieve information about DDR from SMEM

On 4/9/25 5:49 PM, Konrad Dybcio wrote:
> On 4/9/25 5:44 PM, Dmitry Baryshkov wrote:
>> On 09/04/2025 17:47, Konrad Dybcio wrote:
>>> SMEM allows the OS to retrieve information about the DDR memory.
>>> Among that information, is a semi-magic value called 'HBB', or Highest
>>> Bank address Bit, which multimedia drivers (for hardware like Adreno
>>> and MDSS) must retrieve in order to program the IP blocks correctly.
>>>
>>> This series introduces an API to retrieve that value, uses it in the
>>> aforementioned programming sequences and exposes available DDR
>>> frequencies in debugfs (to e.g. pass to aoss_qmp debugfs). More
>>> information can be exposed in the future, as needed.
>>
>> I know that for some platforms HBB differs between GPU and DPU (as it's being programmed currently). Is there a way to check, which values are we going to program:
>>
>> - SM6115, SM6350, SM6375 (13 vs 14)

SM6350 has INFO_V3
SM6375 has INFO_V3_WITH_14_FREQS

>> - SC8180X (15 vs 16)

So I overlooked the fact that DDR info v3 (e.g. on 8180) doesn't provide
the HBB value.. Need to add some more sanity checks there.

Maybe I can think up some fallback logic based on the DDR type reported.

>> - QCM2290 (14 vs 15)

I don't have one on hand, could you please give it a go on your RB1?
I would assume both it and SM6115 also provide v3 though..

Konrad