Re: [PATCH v2 3/4] drm/msm/a6xx: Get HBB dynamically, if available

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 4/21/25 10:13 PM, Rob Clark wrote:
> On Fri, Apr 18, 2025 at 9:00 AM Akhil P Oommen <quic_akhilpo@quicinc.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@quicinc.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@quicinc.com> wrote:
>>>>>>
>>>>>> On 4/10/2025 11:13 PM, Konrad Dybcio wrote:
>>>>>>> From: Konrad Dybcio <konrad.dybcio@oss.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@oss.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

Konrad