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

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Message-ID: <4e265348-3466-49fb-82e2-255205052d1e@oss.qualcomm.com>
Date: Fri, 11 Apr 2025 12:52:32 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: 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>,
        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 4/11/25 12:50 PM, Dmitry Baryshkov wrote:
> On Fri, Apr 11, 2025 at 12:03:03PM +0200, Konrad Dybcio wrote:
>> On 4/11/25 11:57 AM, Dmitry Baryshkov wrote:
>>> On Fri, 11 Apr 2025 at 12:49, Konrad Dybcio
>>> <konrad.dybcio@....qualcomm.com> wrote:
>>>>
>>>> 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
>>>
>>> I'm not completely sure what you mean here. I pointed out that these
>>> platforms disagreed upon the HBB value between the DPU/msm_mdss.c and
>>> a6xx_gpu.c.
>>> In some cases (a610/SM6115 and a619/SM6350) that was intentional to
>>> fix screen corruption issues. I don't remember if it was the case for
>>> QCM2290 or not.
>>
>> As I said below, I couldn't get a good answer yet, as the magic value
>> is not provided explicitly and I'll hopefully be able to derive it from
>> the available data
> 
> I see...
> Is this data even supposed to be poked into? The foo_WITH_bar types
> doesn't sound like a very stable API.

Yeah, it was designed with both the producer and consumer being part
of a single codebase, always having the data structures in sync..

Konrad