Message-ID: <bd9fe032-9844-4b1b-9e25-645b9c6a773d@oss.qualcomm.com>
Date: Wed, 23 Apr 2025 17:07:18 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Rob Clark <robdclark@...il.com>, Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc: Connor Abbott <cwabbott0@...il.com>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>, Kees Cook <kees@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Sean Paul <sean@...rly.run>, Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        dri-devel
 <dri-devel@...ts.freedesktop.org>,
        freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v2 3/4] drm/msm/a6xx: Get HBB dynamically, if available

On 4/23/25 4:56 PM, Rob Clark wrote:
> On Tue, Apr 22, 2025 at 11:55 PM Akhil P Oommen
> <quic_akhilpo@...cinc.com> wrote:
>>
>> On 4/23/2025 5:27 AM, Konrad Dybcio wrote:
>>> On 4/21/25 10:13 PM, Rob Clark wrote:
>>>> On Fri, Apr 18, 2025 at 9:00 AM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>>>>>
>>>>> On 4/18/2025 6:40 AM, Connor Abbott wrote:
>>>>>> On Thu, Apr 17, 2025, 1:50 PM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>>>>>>>
>>>>>>> On 4/17/2025 9:02 PM, Connor Abbott wrote:
>>>>>>>> On Thu, Apr 17, 2025 at 3:45 AM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>>>>>>>>>
>>>>>>>>> On 4/10/2025 11:13 PM, Konrad Dybcio wrote:
>>>>>>>>>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>>>>>>>>>
>>>>>>>>>> The Highest Bank address Bit value can change based on memory type used.
>>>>>>>>>>
>>>>>>>>>> Attempt to retrieve it dynamically, and fall back to a reasonable
>>>>>>>>>> default (the one used prior to this change) on error.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>>>>>>>>> ---
>>>>>>>>>>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 15 ++++++++++++++-
>>>>>>>>>>  1 file changed, 14 insertions(+), 1 deletion(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>>>>>>>>> index 06465bc2d0b4b128cddfcfcaf1fe4252632b6777..a6232b382bd16319f20ae5f8f5e57f38ecc62d9f 100644
>>>>>>>>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>>>>>>>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>>>>>>>>> @@ -13,6 +13,7 @@
>>>>>>>>>>  #include <linux/firmware/qcom/qcom_scm.h>
>>>>>>>>>>  #include <linux/pm_domain.h>
>>>>>>>>>>  #include <linux/soc/qcom/llcc-qcom.h>
>>>>>>>>>> +#include <linux/soc/qcom/smem.h>
>>>>>>>>>>
>>>>>>>>>>  #define GPU_PAS_ID 13
>>>>>>>>>>
>>>>>>>>>> @@ -587,6 +588,8 @@ static void a6xx_set_cp_protect(struct msm_gpu *gpu)
>>>>>>>>>>
>>>>>>>>>>  static void a6xx_calc_ubwc_config(struct adreno_gpu *gpu)
>>>>>>>>>>  {
>>>>>>>>>> +     int hbb;
>>>>>>>>>> +
>>>>>>>>>>       gpu->ubwc_config.rgb565_predicator = 0;
>>>>>>>>>>       gpu->ubwc_config.uavflagprd_inv = 0;
>>>>>>>>>>       gpu->ubwc_config.min_acc_len = 0;
>>>>>>>>>> @@ -635,7 +638,6 @@ static void a6xx_calc_ubwc_config(struct adreno_gpu *gpu)
>>>>>>>>>>           adreno_is_a690(gpu) ||
>>>>>>>>>>           adreno_is_a730(gpu) ||
>>>>>>>>>>           adreno_is_a740_family(gpu)) {
>>>>>>>>>> -             /* TODO: get ddr type from bootloader and use 2 for LPDDR4 */
>>>>>>>>>>               gpu->ubwc_config.highest_bank_bit = 16;
>>>>>>>>>>               gpu->ubwc_config.amsbc = 1;
>>>>>>>>>>               gpu->ubwc_config.rgb565_predicator = 1;
>>>>>>>>>> @@ -664,6 +666,13 @@ static void a6xx_calc_ubwc_config(struct adreno_gpu *gpu)
>>>>>>>>>>               gpu->ubwc_config.highest_bank_bit = 14;
>>>>>>>>>>               gpu->ubwc_config.min_acc_len = 1;
>>>>>>>>>>       }
>>>>>>>>>> +
>>>>>>>>>> +     /* Attempt to retrieve the data from SMEM, keep the above defaults in case of error */
>>>>>>>>>> +     hbb = qcom_smem_dram_get_hbb();
>>>>>>>>>> +     if (hbb < 0)
>>>>>>>>>> +             return;
>>>>>>>>>> +
>>>>>>>>>> +     gpu->ubwc_config.highest_bank_bit = hbb;
>>>>>>>>>
>>>>>>>>> I am worried about blindly relying on SMEM data directly for HBB for
>>>>>>>>> legacy chipsets. There is no guarantee it is accurate on every chipset
>>>>>>>>> and every version of firmware. Also, until recently, this value was
>>>>>>>>> hardcoded in Mesa which matched the value in KMD.
>>>>>>>>
>>>>>>>> To be clear about this, from the moment we introduced host image
>>>>>>>> copies in Mesa we added support for querying the HBB from the kernel,
>>>>>>>> explicitly so that we could do what this series does without Mesa ever
>>>>>>>> breaking. Mesa will never assume the HBB unless the kernel is too old
>>>>>>>> to support querying it. So don't let Mesa be the thing that stops us
>>>>>>>> here.
>>>>>>>
>>>>>>> Thanks for clarifying about Mesa. I still don't trust a data source that
>>>>>>> is unused in production.
>>>>>>
>>>>>> Fair enough, I'm not going to argue with that part. Just wanted to
>>>>>> clear up any confusion about Mesa.
>>>>>>
>>>>>> Although, IIRC kgsl did set different values for a650 depending on
>>>>>> memory type... do you know what source that used?
>>>>>
>>>>> KGSL relies on an undocumented devicetree node populated by bootloader
>>>>> to detect ddrtype and calculates the HBB value based on that.
>>>>
>>>> Would it be reasonable to use the smem value, but if we find the
>>>> undocumented dt property, WARN_ON() if it's value disagrees with smem?
>>>>
>>>> That would at least give some confidence, or justified un-confidence
>>>> about the smem values
>>>
>>> The aforementioned value is populated based on the data that this
>>> driver reads out, and only on the same range of platforms that this
>>> driver happens to cater to
>>
>> Like I suggested privately, can we centralize all ubwc configuration so
>> that it is consistent across all drivers. With that, we will need to
>> maintain a table of ubwc config for each chipset and HBB can be
>> calculated based on the DDR configuration identified from SMEM. Once we
>> migrate the downstream drivers to the new API, we can hopefully move to
>> the HBB value from SMEM. This will ensure that the SMEM data for HBB is
>> accurate in all future chipsets.
>>
> 
> yes please

Alright, I'll get this sorted out 

Konrad

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