linux-kernel - Re: [PATCH v14 5/6] iommu/arm-smmu: add ACTLR data and support for SC7280

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Message-ID: <a882d634-85b3-4c5b-8309-348b4b3d9f0a@quicinc.com>
Date: Tue, 3 Sep 2024 18:29:33 +0530
From: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
To: Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>
CC: <robdclark@...il.com>, <joro@...tes.org>, <jgg@...pe.ca>,
        <jsnitsel@...hat.com>, <robh@...nel.org>,
        <krzysztof.kozlowski@...aro.org>, <quic_c_gdjako@...cinc.com>,
        <dmitry.baryshkov@...aro.org>, <konrad.dybcio@...aro.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 v14 5/6] iommu/arm-smmu: add ACTLR data and support for
 SC7280



On 8/30/2024 6:01 PM, Robin Murphy wrote:
> On 30/08/2024 11:00 am, Bibek Kumar Patro wrote:
>>
>>
>> On 8/27/2024 6:17 PM, Will Deacon wrote:
>>> On Mon, Aug 26, 2024 at 04:33:24PM +0530, Bibek Kumar Patro wrote:
>>>>
>>>>
>>>> On 8/23/2024 9:29 PM, Will Deacon wrote:
>>>>> On Fri, Aug 16, 2024 at 11:12:58PM +0530, Bibek Kumar Patro wrote:
>>>>>> Add ACTLR data table for SC7280 along with support for
>>>>>> same including SC7280 specific implementation operations.
>>>>>>
>>>>>> Signed-off-by: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
>>>>>> ---
>>>>>>    drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 58 
>>>>>> +++++++++++++++++++++-
>>>>>>    1 file changed, 57 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c 
>>>>>> b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>> index dc143b250704..a776c7906c76 100644
>>>>>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>> @@ -31,6 +31,55 @@
>>>>>>    #define PREFETCH_MODERATE    (2 << PREFETCH_SHIFT)
>>>>>>    #define PREFETCH_DEEP        (3 << PREFETCH_SHIFT)
>>>>>>
>>>>>> +static const struct actlr_config sc7280_apps_actlr_cfg[] = {
>>>>>> +    { 0x0800, 0x04e0, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x0900, 0x0402, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x0901, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x0d01, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x1181, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1182, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1183, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1184, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1185, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1186, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1187, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1188, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x1189, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x118b, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x118c, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x118d, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x118e, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x118f, 0x0420, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +    { 0x2000, 0x0020, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x2040, 0x0000, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x2062, 0x0000, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x2080, 0x0020, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x20c0, 0x0020, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x2100, 0x0020, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x2140, 0x0000, PREFETCH_DEFAULT | CMTLB },
>>>>>> +    { 0x2180, 0x0020, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x2181, 0x0004, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x2183, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x2184, 0x0020, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +    { 0x2187, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>>> +};
>>>>>> +
>>>>>> +static const struct actlr_config sc7280_gfx_actlr_cfg[] = {
>>>>>> +    { 0x0000, 0x07ff, PREFETCH_DEEP | CPRE | CMTLB },
>>>>>> +};
>>>>>
>>>>> It's Will "stuck record" Deacon here again to say that I don't think
>>>>> this data belongs in the driver.
>>>>>
>>>>
>>>> Hi Will,
>>>>
>>>> It will be difficult to reach a consensus here, with Robin and the 
>>>> DT folks
>>>> okay to keep it in the driver, while you believe it doesn't belong 
>>>> there.
>>>>
>>>> Robin, Rob, could you please share your thoughts on concluding the 
>>>> placement
>>>> of this prefetch data?
>>>>
>>>> As discussed earlier [1], the prefetch value for each client doesn’t 
>>>> define
>>>> the hardware topology and is implementation-defined register writes 
>>>> used by
>>>> the software driver.
>>>
>>> It does reflect the hardware topology though, doesn't it? Those magic 
>>> hex
>>> masks above refer to stream ids, so the table is hard-coding the 
>>> prefetch
>>> values for particular matches.
>>
>> That is correct in the sense that stream id is mapped to context bank
>> where these configurations are applied.
>> However the other part of it is implementation-defined register/values
>> for which community opinion was register/value kind of data, should not
>> belong to device tree and are not generally approved of.
>>
>> Would also like to point out that the prefetch values are recommended
>> settings and doesn’t mean these are the only configuration which would
>> work for the soc.
>> So the SID-to-prefetch isn't strictly SoC defined but is a software
>> configuration, IMO.
> 
> What's particularly confusing is that most of the IDs encoded here don't 
> actually seem to line up with what's in the respective SoC DTSIs...
> 
> However by this point I'm wary of whether we've lost sight of *why* 
> we're doing this, and that we're deep into begging the question of 
> whether identifying devices by StreamID is the right thing to do in the 
> first place. For example, as best I can tell from a quick skim, we have 
> over 2 dozen lines of data here which all serve the exact same purpose 
> of applying PREFETCH_DEEP | CPRE | CMTLB to instances of 
> "qcom,fastrpc-compute-cb". In general it seems unlikely that the same 
> device would want wildly different prefetch settings across different 
> SoCs, or even between different instances in the same SoC, so I'm really 
> coming round to the conclusion that this data would probably be best 
> handled as an extension of the existing qcom_smmu_client_of_match 
> mechanism.
> 

As per your design idea,do you mean to use qcom_smmu_client_of_match to 
identify the device using compatible string and apply the device 
specific settings for all the SoCs (instead of StreamID based device 
identification) ?

something like this rough snippet(?):

qcom_smmu_find_actlr_client(struct device *dev)
{

	if (of_match_device(qcom_smmu_client_of_match, dev) == 
qcom,fastrpc-compute-cb )
		qcom_smmu_set_actlr_value(dev, (PREFETCH_DEEP | CPRE | CMTLB)); 
/*where (PREFETCH_DEEP | CPRE | CMTLB) is used for compute-cb client.*/

	else if (of_match_device(qcom_smmu_client_of_match, dev) == qcom,adreno )
		qcom_smmu_set_actlr_value(dev, (PREFETCH_SHALLOW | CPRE | CMTLB)); 
/*Where (PREFETCH_SHALLOW | CPRE | CMTLB) is for adreno client. */

}

Let me know if my understanding is incorrect.
Then in this case if different SoC would have a different settings for 
same device, then everytime a new compatible would be necessary for same 
device on different SoC?

On similar lines there is another TBU based approach which I can think 
of. Identify the TBU -> Identify clients from TopoID derived from SID 
range specified in qcom,stream-id-range -> Apply the client
specific settings ?

Both approaches would be driver-based, as they are now.

Also I'd like to point out that in the current design, since we fixed 
the smr_is_subset arguments to make the stream IDs a subset of entries 
in the actlr_cfg table, we can reduce the number of entries in the 
table. This way, fewer SID-mask pairs can accommodate several stream IDs.

Thanks & regards,
Bibek

> Thanks,
> Robin.
> 
>>
>>> If I run on a different SoC configuration > with the same table, then 
>>> the prefetch settings will be applied to the
>>> wrong devices. How is that not hardware topology?
>>>
>>
>> The configuration table is tied to SoC compatible string however as I
>> mentioned above, its basically a s/w recommended setting.
>> (using prefetch settings other than the recommended values e.g 
>> PREFECH_DEFAULT instead of PREFETCH_DEEP would not render the device 
>> unusable unlike changing stream-ids which can make it unusable).
>>
>> Since it is implementation specific we cannot have a generic DT binding,
>> tying stream ids to these recommended settings.
>> Even with qcom specific binding due to dependency on implementation, not
>> sure if we would be able to maintain consistency.
>>
>> So from maintenance perspective carrying these in driver appear to be
>> simpler/flexible. And if it doesn’t violate existing precedence, we
>> would prefer to carry it that way.
>>
>> This parallels how _"QoS settings"_ are handled within the driver 
>> (similar to this example [1]).
>>
>> [1]. 
>> https://lore.kernel.org/linux-arm-msm/20231030-sc8280xp-dpu-safe-lut-v1-1-6d485d7b428f@quicinc.com/#t
>>
>> Thanks & regards,
>> Bibek
>>
>>> WIll