linux-kernel - Re: [PATCH v4 3/5] iommu/arm-smmu: add ACTLR data and support for SM8550

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Message-ID: <334bc814-07d2-4966-93e3-f2cfbabc15b2@quicinc.com>
Date: Tue, 19 Dec 2023 16:06:48 +0530
From: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Konrad Dybcio <konrad.dybcio@...aro.org>,
        Robin Murphy
	<robin.murphy@....com>, <will@...nel.org>,
        <joro@...tes.org>, <jsnitsel@...hat.com>, <quic_bjorande@...cinc.com>,
        <mani@...nel.org>, <quic_eberman@...cinc.com>,
        <robdclark@...omium.org>, <u.kleine-koenig@...gutronix.de>,
        <robh@...nel.org>, <vladimir.oltean@....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 v4 3/5] iommu/arm-smmu: add ACTLR data and support for
 SM8550



On 12/19/2023 3:51 PM, Dmitry Baryshkov wrote:
> On Tue, 19 Dec 2023 at 10:25, Bibek Kumar Patro
> <quic_bibekkum@...cinc.com> wrote:
>>
>>
>>
>> On 12/18/2023 7:51 PM, Dmitry Baryshkov wrote:
>>> On 18/12/2023 13:23, Bibek Kumar Patro wrote:
>>>>
>>>>
>>>> On 12/16/2023 9:45 PM, Dmitry Baryshkov wrote:
>>>>> On 16/12/2023 02:03, Konrad Dybcio wrote:
>>>>>> On 15.12.2023 13:54, Robin Murphy wrote:
>>>>>>> On 2023-12-15 12:20 pm, Bibek Kumar Patro wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 12/15/2023 4:14 PM, Dmitry Baryshkov wrote:
>>>>>>>>> On Fri, 15 Dec 2023 at 12:19, 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 | 89
>>>>>>>>>> ++++++++++++++++++++++
>>>>>>>>>>     1 file changed, 89 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>>>>> b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>>>>> index cb49291f5233..d2006f610243 100644
>>>>>>>>>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>>>>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
>>>>>>>>>> @@ -20,6 +20,85 @@ struct actlr_config {
>>>>>>>>>>            u32 actlr;
>>>>>>>>>>     };
>>>>>>>>>>
>>>>>>>>>> +/*
>>>>>>>>>> + * SMMU-500 TRM defines BIT(0) as CMTLB (Enable context caching
>>>>>>>>>> in the
>>>>>>>>>> + * macro TLB) and BIT(1) as CPRE (Enable context caching in the
>>>>>>>>>> prefetch
>>>>>>>>>> + * buffer). The remaining bits are implementation defined and
>>>>>>>>>> vary across
>>>>>>>>>> + * SoCs.
>>>>>>>>>> + */
>>>>>>>>>> +
>>>>>>>>>> +#define PREFETCH_DEFAULT       0
>>>>>>>>>> +#define PREFETCH_SHALLOW       BIT(8)
>>>>>>>>>> +#define PREFETCH_MODERATE      BIT(9)
>>>>>>>>>> +#define PREFETCH_DEEP          (BIT(9) | BIT(8))
>>>>>>>>>
>>>>>>>>> I thin the following might be more correct:
>>>>>>>>>
>>>>>>>>> #include <linux/bitfield.h>
>>>>>>>>>
>>>>>>>>> #define PREFETCH_MASK GENMASK(9, 8)
>>>>>>>>> #define PREFETCH_DEFAULT FIELD_PREP(PREFETCH_MASK, 0)
>>>>>>>>> #define PREFETCH_SHALLOW FIELD_PREP(PREFETCH_MASK, 1)
>>>>>>>>> #define PREFETCH_MODERATE FIELD_PREP(PREFETCH_MASK, 2)
>>>>>>>>> #define PREFETCH_DEEP FIELD_PREP(PREFETCH_MASK, 3)
>>>>>>>>>
>>>>>>>>
>>>>>>>> Ack, thanks for this suggestion. Let me try this out using
>>>>>>>> GENMASK. Once tested, will take care of this in next version.
>>>>>>>
>>>>>>> FWIW the more typical usage would be to just define the named
>>>>>>> macros for the raw field values, then put the FIELD_PREP() at the
>>>>>>> point of use. However in this case that's liable to get pretty
>>>>>>> verbose, so although I'm usually a fan of bitfield.h, the most
>>>>>>> readable option here might actually be to stick with simpler
>>>>>>> definitions of "(0 << 8)", "(1 << 8)", etc. However it's not really
>>>>>>> a big deal either way, and I defer to whatever Dmitry and Konrad
>>>>>>> prefer, since they're the ones looking after arm-smmu-qcom the most :)
>>>>>> My 5 cents would be to just use the "common" style of doing this, so:
>>>>>>
>>>>>> #define ACTRL_PREFETCH    GENMASK(9, 8)
>>>>>>    #define PREFETCH_DEFAULT 0
>>>>>>    #define PREFETCH_SHALLOW 1
>>>>>>    #define PREFETCH_MODERATE 2
>>>>>>    #define PREFETCH_DEEP 3
>>>>>>
>>>>>> and then use
>>>>>>
>>>>>> | FIELD_PREP(ACTRL_PREFETCH, PREFETCH_x)
>>>>>>
>>>>>> it can get verbose, but.. arguably that's good, since you really want
>>>>>> to make sure the right bits are set here
>>>>>
>>>>> Sounds good to me.
>>>>>
>>>>
>>>> Konrad, Dimitry, just checked FIELD_PREP() implementation
>>>>
>>>> #define FIELD_FIT(_mask, _val)
>>>> ({                                                              \
>>>>                    __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");  \
>>>>                    ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
>>>> })
>>>>
>>>> since it is defined as a block, it won't be possible to use FIELD_PREP
>>>> in macro or as a structure value, and can only be used inside a
>>>> block/function. Orelse would show compilation errors as following
>>>>
>>>> kernel/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c:94:20: note: in
>>>> expansion of macro 'PREFETCH_SHALLOW'
>>>>     { 0x1947, 0x0000, PREFETCH_SHALLOW | CPRE | CMTLB },
>>>>                       ^
>>>> kernel/include/linux/bitfield.h:113:2: error: braced-group within
>>>> expression allowed only inside a function
>>>>     ({        \
>>>>     ^
>>>>
>>>> So as per my understanding I think, we might need to go ahead with the
>>>> generic implementation only. Let me know if I missed something.
>>>
>>> Then anyway (foo << bar) is better compared to BIT(n) | BIT(m).
>>>
>>
>> Sure Dmitry, (foo << bar) would be simpler as well as Robin mentioned
>> earlier in his reply.
>> I can implement the defines as:
>>
>> #define PREFETCH_DEFAULT       0
>> #define PREFETCH_SHALLOW       (1 << 8)
>> #define PREFETCH_MODERATE      (1 << 9)
> 
> 2 << 8. Isn't that hard.
> 

Ah, right. This is nice! .
Will use 2 << 8 instead. Thanks for the suggestion.

Thanks,
Bibek

>> #define PREFETCH_DEEP          (3 << 8)
>>
>> This should be okay I think ?
>>
>> Thanks,
>> Bibek
>>
> 
>