linux-kernel - Re: [PATCH 1/1] iommu/arm-smmu-qcom: remove runtime pm enabling for TBU driver

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Message-ID: <3cb1da06-88e3-4dd2-b56c-e0ab725ef6b2@quicinc.com>
Date: Tue, 13 Aug 2024 15:06:23 +0300
From: Georgi Djakov <quic_c_gdjako@...cinc.com>
To: Zhenhua Huang <quic_zhenhuah@...cinc.com>,
        Pranjal Shrivastava
	<praan@...gle.com>
CC: <robdclark@...il.com>, <will@...nel.org>, <robin.murphy@....com>,
        <joro@...tes.org>, <iommu@...ts.linux.dev>,
        <linux-arm-msm@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <dmitry.baryshkov@...aro.org>, Georgi Djakov <djakov@...nel.org>
Subject: Re: [PATCH 1/1] iommu/arm-smmu-qcom: remove runtime pm enabling for
 TBU driver

Hi Zhenhua,

On 8/13/2024 10:56 AM, Zhenhua Huang wrote:
> 
> On 2024/8/13 15:20, Pranjal Shrivastava wrote:
>> On Tue, Aug 13, 2024 at 10:37:33AM +0800, Zhenhua Huang wrote:
>>>
>>> On 2024/8/12 21:25, Pranjal Shrivastava wrote:
>>>> On Tue, Jul 30, 2024 at 06:30:43PM +0800, Zhenhua Huang wrote:
>>>>> TBU driver has no runtime pm support now, adding pm_runtime_enable()
>>>>> seems to be useless. Remove it.
>>>>>
>>>>> Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
[..]
>> I agree that there are no pm_runtime_suspend/resume calls within the TBU
>> driver. I'm just trying to understand why was pm_runtime enabled here
>> earlier (since it's not implemented) in order to ensure that removing it
>> doesn't cause further troubles?
> 
> See above my assumption, need Georgi to comment but.

Thank you for looking at the code! Your assumptions are mostly correct,
but if you try this patch on a real sdm845 device you will notice some
issues. So it's actually needed to re-configure the power-domains, three
of which (MMNOC GDSCs) are requiring this because of a HW bug. I should
have put a comment in the code to avoid confusion, but it took me some
time to confirm it.

I have sent a patch to handle this more cleanly:
https://lore.kernel.org/lkml/20240813120015.3242787-1-quic_c_gdjako@quicinc.com

So we should not remove the runtime pm calls until some version of the
above patch gets merged.

Thanks,
Georgi

>> I see Georgi added it as a part of
>> https://lore.kernel.org/all/20240704010759.507798-1-quic_c_gdjako@quicinc.com/
>>
>> But I'm unsure why was it required to fix that bug?
> 
> I'm just thinking it is dead code and want to see if my understanding is correct.