linux-kernel - Re: [PATCH v2 2/3] iommu/arm-smmu: add ACTLR data and support for SM8550

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Date:   Wed, 15 Nov 2023 17:42:00 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Bibek Kumar Patro <quic_bibekkum@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     will@...nel.org, robin.murphy@....com, joro@...tes.org,
        a39.skl@...il.com, quic_pkondeti@...cinc.com,
        quic_molvera@...cinc.com, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, qipl.kernel.upstream@...cinc.com
Subject: Re: [PATCH v2 2/3] iommu/arm-smmu: add ACTLR data and support for
 SM8550



On 11/15/23 13:49, Bibek Kumar Patro wrote:
> 
> 
> On 11/15/2023 4:15 PM, Dmitry Baryshkov wrote:
>> On Wed, 15 Nov 2023 at 11:51, Bibek Kumar Patro
>> <quic_bibekkum@...cinc.com> wrote:
>>>
>>>
>>>
>>> On 11/15/2023 3:08 PM, Dmitry Baryshkov wrote:
>>>> On Wed, 15 Nov 2023 at 11:22, Bibek Kumar Patro
>>>> <quic_bibekkum@...cinc.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 11/14/2023 7:42 PM, Dmitry Baryshkov wrote:
>>>>>> On Tue, 14 Nov 2023 at 15:57, Bibek Kumar Patro
>>>>>> <quic_bibekkum@...cinc.com> wrote:
>>>>>>>
>>>>>>> Add ACTLR data table for SM8550 along with support for
>>>>>>> same including SM8550 specific implementation operations.
>>>>>>>
>>>>>>> Signed-off-by: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
>>>>>>> ---
>>>>>>>     drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 92 +++++++++++++++++++++-
>>>>>>>     1 file changed, 88 insertions(+), 4 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>> index 578c662c7c30..0eaf6f2a2e49 100644
>>>>>>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>> @@ -25,6 +25,70 @@ struct actlr_data {
>>>>>>>            u32 actlr;
>>>>>>>     };
>>>>>>>
>>>>>>> +#define PRE_FETCH_1    0
>>>>>>> +#define PRE_FETCH_2    BIT(8)
>>>>>>> +#define PRE_FETCH_3    (BIT(9) | BIT(8))
>>>>>>
>>>>>> What is the difference between PRE_FETCH_3 and PRE_FETCH_2? And
>>>>>> PRE_FETCH_1? Are these real numbers that refer to some amount / count
>>>>>> or just dummy names?
>>>>>>
>>>>>
>>>>> No,these are not real numbers, but prefetch settings for a particular
>>>>> perfect configuration.
>>>>
>>>> Then I'd ask for some better names or descriptions.
>>>>
>>>
>>> Noted, PREFETCH_SETTING_n / PREFETCH_OPTION_n sounds like a better name
>>> in the following case. Would it be okay to use this name instead?
>>
>> Not really.
>>
> 
> Any suggestion you have in mind, if not this nomenclature?
Dmitry's concern seems to be that you provide:

PRE_FETCH_1 /* prefetcher with settings preset no. 1 */
PRE_FETCH_2 /* prefetcher with settings preset no. 2 */
PRE_FETCH_3 /* prefetcher with settings preset no. 3 */

whereas it would be both useful and interesting to see what these
settings mean, i.e. what differences there are between all of
these presets.

Konrad