linux-kernel - Re: [PATCH V2] iommu/arm-smmu: add actlr settings for mdss on sa8775p platform

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Message-ID: <09b933ab-eba4-47c2-a667-370dbeda2749@oss.qualcomm.com>
Date: Thu, 20 Nov 2025 13:33:29 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Charan Teja Kalla <charan.kalla@....qualcomm.com>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: robin.clark@....qualcomm.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
Subject: Re: [PATCH V2] iommu/arm-smmu: add actlr settings for mdss on sa8775p
 platform

On 11/19/25 7:06 PM, Charan Teja Kalla wrote:
> 
> 
> On 11/18/2025 11:33 PM, Dmitry Baryshkov wrote:
>>> Add ACTLR settings for the mdss device on Qualcomm SA8775P platform.
>>> This is achieved by adding compatibility string for mdss in the actlr
>>> client of match table.
>>>
>>> Signed-off-by: Charan Teja Kalla <charan.kalla@....qualcomm.com>
>>> ---
>>>
>>> Changed from V1:
>>>   1) Added actlr setting only for MDSS and dropped for fastrpc. -- konrad
>>>   2) ACTLR table is updated per alphanumeric order -- konrad 
>>>   https://lore.kernel.org/all/20251105075307.1658329-1-
>>> charan.kalla@....qualcomm.com/
>>>
>>>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>> index 62874b18f645..0b400e22cb00 100644
>>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>> @@ -41,6 +41,8 @@ static const struct of_device_id qcom_smmu_actlr_client_of_match[] = {
>>>  			.data = (const void *) (PREFETCH_DEEP | CPRE | CMTLB) },
>>>  	{ .compatible = "qcom,fastrpc",
>>>  			.data = (const void *) (PREFETCH_DEEP | CPRE | CMTLB) },
>>> +	{ .compatible = "qcom,sa8775p-mdss",
>>> +			.data = (const void *) (PREFETCH_DEFAULT | CMTLB) },
>> What's the difference from SC7280? Why don't we need to set CPRE?
> 
> Sorry, I'm really not sure If your question imply to talk about the IP
> level difference compared to SC7280 for mdss?

"SC7280 has MDSS, SA8775P also has (a slightly different) MDSS, is there
a reason these two have different settings"

> Regarding why don't we need CPRE -- these are QoS settings that does
> control how well hw behaves i.e., related to performance settings not
> the functional ones.  I guess, these settings are derived from factors
> like how many masters are sharing a TBU, how crucial are masters using
> that TBU(like important ones may be allowed to +7 or +15 and may be
> others upto only +1 prefetch).

And this is a good answer

Perhaps you could reword it a little and put in the commit message to
make it clear in case anyone has the same question in a year or so

Konrad