Re: [RFC PATCH 1/4] drm/msm: register a fault handler for display mmu faults

[Abhinav Kumar <quic_abhinavk@quicinc.com>]

On 6/21/2024 4:35 PM, Abhinav Kumar wrote:
> 
> 
> On 5/19/2024 1:38 AM, Dmitry Baryshkov wrote:
>> On Fri, May 17, 2024 at 04:37:56PM -0700, Abhinav Kumar wrote:
>>> In preparation to register a iommu fault handler for display
>>> related modules, register a fault handler for the backing
>>> mmu object of msm_kms.
>>>
>>> Currently, the fault handler only captures the display snapshot
>>> but we can expand this later if more information needs to be
>>> added to debug display mmu faults.
>>>
>>> Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
>>> ---
>>>   drivers/gpu/drm/msm/msm_kms.c | 25 +++++++++++++++++++++++++
>>>   1 file changed, 25 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/msm/msm_kms.c 
>>> b/drivers/gpu/drm/msm/msm_kms.c
>>> index af6a6fcb1173..62c8e6163e81 100644
>>> --- a/drivers/gpu/drm/msm/msm_kms.c
>>> +++ b/drivers/gpu/drm/msm/msm_kms.c
>>> @@ -200,6 +200,28 @@ struct msm_gem_address_space 
>>> *msm_kms_init_aspace(struct drm_device *dev)
>>>       return aspace;
>>>   }
>>> +static int msm_kms_fault_handler(void *arg, unsigned long iova, int 
>>> flags, void *data)
>>> +{
>>> +    struct msm_kms *kms = arg;
>>> +    struct msm_disp_state *state;
>>> +    int ret;
>>> +
>>> +    ret = mutex_lock_interruptible(&kms->dump_mutex);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    state = msm_disp_snapshot_state_sync(kms);
>>> +
>>> +    mutex_unlock(&kms->dump_mutex);
>>> +
>>> +    if (IS_ERR(state)) {
>>> +        DRM_DEV_ERROR(kms->dev->dev, "failed to capture snapshot\n");
>>> +        return PTR_ERR(state);
>>> +    }
>>> +
>>> +    return 0;
>>
>> Hmm, after reading the rest of the code, this means that we won't get
>> the error on the console. Could you please change this to -ENOSYS?
>>
> 
> I am perhaps missing something here. Are you referring to this 
> documentation?
> 
>   * Specifically, -ENOSYS is returned if a fault handler isn't installed
>   * (though fault handlers can also return -ENOSYS, in case they want to
>   * elicit the default behavior of the IOMMU drivers).
>   */
> int report_iommu_fault(struct iommu_domain *domain, struct device *dev,
>                         unsigned long iova, int flags)
> 
> Doesnt this mean ENOSYS is when fault handler is not installed?
> 
> Because the console print will come if we return 0?
> 
>          if (!report_iommu_fault(ctx->domain, ctx->dev, iova, 0)) {
>                  dev_err_ratelimited(ctx->dev,
>                                      "Unhandled context fault: fsr=0x%x, "
>                                      "iova=0x%016llx, fsynr=0x%x, cb=%d\n",
>                                      fsr, iova, fsynr, ctx->asid);
>          }
> 

I was checking the wrong place, you are correct.

I will return ENOSYS here.

Thanks.

>>> +}
>>> +
>>>   void msm_drm_kms_uninit(struct device *dev)
>>>   {
>>>       struct platform_device *pdev = to_platform_device(dev);
>>> @@ -261,6 +283,9 @@ int msm_drm_kms_init(struct device *dev, const 
>>> struct drm_driver *drv)
>>>           goto err_msm_uninit;
>>>       }
>>> +    if (kms->aspace)
>>> +        msm_mmu_set_fault_handler(kms->aspace->mmu, kms, 
>>> msm_kms_fault_handler);
>>> +
>>>       drm_helper_move_panel_connectors_to_head(ddev);
>>>       drm_for_each_crtc(crtc, ddev) {
>>> -- 
>>> 2.44.0
>>>
>>