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SubjectRe: [PATCH 2/6] arm64: dts: qcom: sm8250: add apps_smmu node
On 2020-05-25 17:23, Jonathan Marek wrote:
> On 5/25/20 7:40 AM, Sai Prakash Ranjan wrote:
>> On 2020-05-25 16:57, Jonathan Marek wrote:
>>> On 5/25/20 7:17 AM, Sai Prakash Ranjan wrote:
>>>> Hi,
>>>>
>>>> On 2020-05-25 16:38, Jonathan Marek wrote:
>>>>> On 5/25/20 6:54 AM, Sai Prakash Ranjan wrote:
>>>>>> On 2020-05-25 15:39, Jonathan Marek wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 5/25/20 5:42 AM, Sai Prakash Ranjan wrote:
>>>>>>>> Hi Jonathan,
>>>>>>>>
>>>>>>>> On 2020-05-24 08:08, Jonathan Marek wrote:
>>>>>>>>> Add the apps_smmu node for sm8250. Note that adding the iommus
>>>>>>>>> field for
>>>>>>>>> UFS is required because initializing the iommu removes the
>>>>>>>>> bypass mapping
>>>>>>>>> that created by the bootloader.
>>>>>>>>>
>>>>>>>>
>>>>>>>> This statement doesn't seem right, you can just say since the
>>>>>>>> bypass is disabled
>>>>>>>> by default now, we need to add this property to enable
>>>>>>>> translation and avoid global faults.
>>>>>>>>
>>>>>>>
>>>>>>> If I use this patch [1] then the UFS iommu property isn't needed.
>>>>>>> In
>>>>>>> downstream, the identity (bypass?) stream mapping is inherited
>>>>>>> from
>>>>>>> the bootloader, and UFS is used without any iommu property.
>>>>>>> Setting
>>>>>>> ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=n doesn't make it work on its
>>>>>>> own
>>>>>>> (without the UFS iommu property), so there's more to it than just
>>>>>>> "bypass is disabled by default now".
>>>>>>>
>>>>>>> https://patchwork.kernel.org/patch/11310757/
>>>>>>>
>>>>>>
>>>>>> "iommus" property is not about inheriting stream mapping from
>>>>>> bootloader,
>>>>>> it is used to enable SMMU address translation for the
>>>>>> corresponding
>>>>>> master when specified. So when you have disabled bypass, i.e.,
>>>>>> ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=y or via cmdline
>>>>>> "arm-smmu.disable_bypass=1"
>>>>>> and iommus property with SID and mask is not specified, then it
>>>>>> will result
>>>>>> in SMMU global faults.
>>>>>>
>>>>>> Downstream has bypass
>>>>>> enabled(ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=n),so you
>>>>>> won't see any global faults if you do not have iommus property.
>>>>>>
>>>>>> Patch in your link is for display because of the usecase for
>>>>>> splash screen
>>>>>> on android and some other devices where the bootloader will
>>>>>> configure SMMU,
>>>>>> it has not yet merged and not likely to get merged in the current
>>>>>> state.
>>>>>>
>>>>>> So yes "there is *not* much more to it than bypass is disabled by
>>>>>> default now"
>>>>>> and you have to specify "iommus" for the master devices or you
>>>>>> should enable bypass,
>>>>>> i.e., ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=n or
>>>>>> arm-smmu.disable_bypass=n
>>>>>>
>>>>>> Try without the patch in the link and without iommus for UFS and
>>>>>> ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=y and you will see.
>>>>>>
>>>>>> -Sai
>>>>>
>>>>> I know that the "iommus" property is not about inheriting stream
>>>>> mapping. Probing the iommu removes the stream mapping created by
>>>>> the
>>>>> bootloader, the iommus property is added so that new mappings are
>>>>> created to replace what was removed.
>>>>>
>>>>> You seem to be under the impression that the SM8150/SM8250
>>>>> bootloader
>>>>> does not configure SMMU. It does, for both UFS and SDHC, just like
>>>>> it
>>>>> does for display/splash screen on some devices.
>>>>>
>>>>
>>>> It could be that bootloader does configure SMMU for UFS and SDHC,
>>>> but the
>>>> upstream SMMU driver doesnt allow to inherit stream mapping from the
>>>> bootloader
>>>> yet, so adding iommus property based on the assumption that it is
>>>> inherited seems
>>>> wrong.
>>>>
>>>
>>> I never said adding the iommus property is for inheriting stream
>>> mapping. I mentioned inheriting to say UFS works without the iommus
>>> property on downstream (it inherits a identity/bypass mapping).
>>>
>>
>> Your commit description says "adding the iommus field for UFS is
>> required
>> because initializing the iommu removes the bypass mapping that created
>> by the
>> bootloader". So here it would mean like iommus property for UFS is not
>> for
>> enabling address translation by SMMU for UFS but to avoid removing
>> mappings
>> created by the bootloader which is not exactly what iommus property is
>> for.
>>
>
> I guess the commit message is ambiguous, that's not what I meant. Is
> "Now that the kernel initializes the iommu, the bypass mappings set by
> the bootloader are cleared. Adding the iommus property is required so
> that new mappings are created for UFS." better?
>

Yes looks good.

>>>>> With either value of ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT, it will
>>>>> not
>>>>> work without the iommus property.
>>>>
>>>> I'm pretty sure that if you have
>>>> ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=n and
>>>> without iommus, it should work.
>>>>
>>>
>>> It doesn't work, with either ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=n or
>>> ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT=y.
>>>
>>
>> Ok since you are very sure about this, I will try with your patches on
>> SM8150 MTP tomorrow since I do not have access to one now.
>> Also just to make sure, please remove all the extra SMMU patches you
>> have
>> in your tree which are not yet merged or from downstream kernel.
>>
>
> FYI, I have a branch [1] integrating patches for upstream. All the
> patches up to 34fff8a519cc075933 ("arm64: dts: qcom: add sm8250 GPU
> nodes") have been submitted (and the patches after that are
> unnecessary for testing on sm8150).
>
> [1] https://github.com/flto/linux/commits/sm8x50-upstream
>

Thanks, I will test this out.

-Sai
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