[PATCH v3 6/8] drm/msm/dpu: add support for MDP_TOP blackhole

[Dmitry Baryshkov]

On 16/11/2022 11:30, Abhinav Kumar wrote:
> 
> 
> On 11/16/2022 12:19 AM, Dmitry Baryshkov wrote:
>> On 16/11/2022 10:50, Abhinav Kumar wrote:
>>>
>>>
>>> On 11/4/2022 6:03 AM, Dmitry Baryshkov wrote:
>>>> On sm8450 a register block was removed from MDP TOP. Accessing it 
>>>> during
>>>> snapshotting results in NoC errors / immediate reboot. Skip accessing
>>>> these registers during snapshot.
>>>>
>>>> Tested-by: Vinod Koul <vkoul at kernel.org>
>>>> Reviewed-by: Vinod Koul <vkoul at kernel.org>
>>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>>
>>> I am confused with both the ordering and the split of this patch.
>>>
>>> You have defined DPU_MDP_PERIPH_0_REMOVED in the catalog header file 
>>> in this patch but used it in the next.
>>>
>>> But you also have code in this patch which relies on setting of this 
>>> bit.
>>>
>>> So if this patch is taken without the next, it will still crash.
>>
>> It will not crash if this patch is taken without the next one. Without 
>> the next patch the DPU driver will not match and bind against the 
>> qcom,sm8450-dpu device.
> 
> Ah okay, I just now saw that you have the compatible change also in the 
> next patch.
> 
>>
>> So, the ordering is quite logical from my point of view:
>> - add support for all the features required for the device
>> - add the device compat string & catalog entry
>>
>>>
>>> Rather, you should combine the define part of this patch to the next 
>>> patch in the series 
>>> https://patchwork.freedesktop.org/patch/510114/?series=108883&rev=3 , 
>>> then move that one in front of this patch.
>>
>> No. This way we'll have a state (after adding the next patch) when the 
>> sm8450 support is enabled, but the top-hole is not handled, leading to 
>> a crash.
>>
> 
> What if you split the compatible to a separate patch like what SM8350 did.
> 
> https://patchwork.freedesktop.org/patch/511659/?series=110924&rev=1
> 
> So, we have hw catalog changes ---> snapshot fix ---> add the compatible.

I don't see any good reason to do this. Adding a define without backing 
implementation is a bad idea in my opinion.

Regarding splitting the hw_catalog and compat. I have always considered 
the hw catalog entry as of_device_id.data. In other words, a devices' 
match data, which makes a little sense without compat entry.

With the current approach each patch is atomic, it changes single point 
or adds a single feature, etc.

> 
> That will make both of us happy?
> 
>>>
>>> So that its much more coherent that you defined 
>>> DPU_MDP_PERIPH_0_REMOVED both in the catalog header and used it in 
>>> the catalog.c file and the in the next change you used the caps to 
>>> avoid touching that register.
>>
>> I'd say it's rather strange way. When I see a define/feature addition, 
>> I'd prefer to seethe implementation too.
>>
>>> Regarding the TOP hole itself, I need one day to investigate this. I 
>>> am waiting for permissions to the documentation.
>>>
>>> If i cannot get access by the time you have re-ordered this, I will 
>>> ack this once the reorder is done within a day.
>>
>>
>> For the reference: [1]
>>
>> [1] 
>> https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/commit/f9ff8af5b640147f3651c23551c60f81f62874b1
>>
>>>
>>>> ---
>>>>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h |  1 +
>>>>   drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c        | 11 +++++++++--
>>>>   2 files changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h 
>>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
>>>> index 38aa38ab1568..4730f8268f2a 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
>>>> @@ -92,6 +92,7 @@ enum {
>>>>       DPU_MDP_UBWC_1_0,
>>>>       DPU_MDP_UBWC_1_5,
>>>>       DPU_MDP_AUDIO_SELECT,
>>>> +    DPU_MDP_PERIPH_0_REMOVED,
>>>>       DPU_MDP_MAX
>>>>   };
>>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c 
>>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
>>>> index f3660cd14f4f..95d8765c1c53 100644
>>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
>>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
>>>> @@ -927,8 +927,15 @@ static void dpu_kms_mdp_snapshot(struct 
>>>> msm_disp_state *disp_state, struct msm_k
>>>>           msm_disp_snapshot_add_block(disp_state, cat->wb[i].len,
>>>>                   dpu_kms->mmio + cat->wb[i].base, "wb_%d", i);
>>>> -    msm_disp_snapshot_add_block(disp_state, cat->mdp[0].len,
>>>> -            dpu_kms->mmio + cat->mdp[0].base, "top");
>>>> +    if (dpu_kms->hw_mdp->caps->features & 
>>>> BIT(DPU_MDP_PERIPH_0_REMOVED)) {
>>>> +        msm_disp_snapshot_add_block(disp_state, 0x380,
>>>> +                dpu_kms->mmio + cat->mdp[0].base, "top");
>>>> +        msm_disp_snapshot_add_block(disp_state, cat->mdp[0].len - 
>>>> 0x3a8,
>>>> +                dpu_kms->mmio + cat->mdp[0].base + 0x3a8, "top_2");
>>>> +    } else {
>>>> +        msm_disp_snapshot_add_block(disp_state, cat->mdp[0].len,
>>>> +                dpu_kms->mmio + cat->mdp[0].base, "top");
>>>> +    }
>>>>       pm_runtime_put_sync(&dpu_kms->pdev->dev);
>>>>   }
>>

-- 
With best wishes
Dmitry