linux-kernel - Re: [RESEND PATCH v17 5/5] iommu/arm-smmu: Add support for qcom,smmu-v2 variant

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Message-ID: <a6ea5f85-db61-3f6d-9dba-65eacc8f739d@codeaurora.org>
Date:   Mon, 26 Nov 2018 23:25:20 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     thor.thayer@...ux.intel.com, Will Deacon <will.deacon@....com>
Cc:     Tomasz Figa <tfiga@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
        sboyd@...nel.org, linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        open list <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>, alex.williamson@...hat.com,
        robh+dt <robh+dt@...nel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [RESEND PATCH v17 5/5] iommu/arm-smmu: Add support for
 qcom,smmu-v2 variant

Hi Thor,


On 11/26/2018 8:11 PM, Thor Thayer wrote:
> Hi Vivek,
>
> On 11/26/18 4:55 AM, Vivek Gautam wrote:
>>
>> On 11/24/2018 12:04 AM, Will Deacon wrote:
>>> On Fri, Nov 23, 2018 at 03:06:29PM +0530, Vivek Gautam wrote:
>>>> On Fri, Nov 23, 2018 at 2:52 PM Tomasz Figa <tfiga@...omium.org> 
>>>> wrote:
>>>>> On Fri, Nov 23, 2018 at 6:13 PM Vivek Gautam
>>>>> <vivek.gautam@...eaurora.org> wrote:
>>>>>> On Wed, Nov 21, 2018 at 11:09 PM Will Deacon 
>>>>>> <will.deacon@....com> wrote:
>>>>>>> On Fri, Nov 16, 2018 at 04:54:30PM +0530, Vivek Gautam wrote:
>>>>>>>> @@ -2026,6 +2027,17 @@ ARM_SMMU_MATCH_DATA(arm_mmu401, 
>>>>>>>> ARM_SMMU_V1_64K, GENERIC_SMMU);
>>>>>>>>   ARM_SMMU_MATCH_DATA(arm_mmu500, ARM_SMMU_V2, ARM_MMU500);
>>>>>>>>   ARM_SMMU_MATCH_DATA(cavium_smmuv2, ARM_SMMU_V2, CAVIUM_SMMUV2);
>>>>>>>>
>>>>>>>> +static const char * const qcom_smmuv2_clks[] = {
>>>>>>>> +     "bus", "iface",
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +static const struct arm_smmu_match_data qcom_smmuv2 = {
>>>>>>>> +     .version = ARM_SMMU_V2,
>>>>>>>> +     .model = QCOM_SMMUV2,
>>>>>>>> +     .clks = qcom_smmuv2_clks,
>>>>>>>> +     .num_clks = ARRAY_SIZE(qcom_smmuv2_clks),
>>>>>>>> +};
>>>>>>> These seems redundant if we go down the route proposed by Thor, 
>>>>>>> where we
>>>>>>> just pull all of the clocks out of the device-tree. In which 
>>>>>>> case, why
>>>>>>> do we need this match_data at all?
>>>>>> Which is better? Driver relying solely on the device tree to tell
>>>>>> which all clocks
>>>>>> are required to be enabled,
>>>>>> or, the driver deciding itself based on the platform's match data,
>>>>>> that it should
>>>>>> have X, Y, & Z clocks that should be supplied from the device tree.
>>>>> The former would simplify the driver, but would also make it
>>>>> impossible to spot mistakes in DT, which would ultimately surface out
>>>>> as very hard to debug bugs (likely complete system lockups).
>>>> Thanks.
>>>> Yea, this is how I understand things presently. Relying on device tree
>>>> puts the things out of driver's control.
>>> But it also has the undesirable effect of having to update the driver
>>> code whenever we want to add support for a new SMMU implementation. If
>>> we do this all in the DT, as Thor is trying to do, then older kernels
>>> will work well with new hardware.
>>>
>>>> Hi Will,
>>>> Am I unable to understand the intentions here for Thor's clock-fetch
>>>> design change?
>>> I'm having trouble parsing your question, sorry. Please work with Thor
>>> so that we have a single way to get the clock information. My 
>>> preference
>>> is to take it from the firmware, for the reason I stated above.
>> Hi Will,
>>
>> Sure, thanks. I will work with Thor to get this going.
>>
>> Hi Thor,
>> Does it sound okay to you to squash your patch [1] into my patch [2] 
>> with
>> your 'Signed-off-by' tag?
>> I will update the commit log to include the information about getting
>> clock details from device tree.
>>
>> [1] https://patchwork.kernel.org/patch/10628725/
>> [2] https://patchwork.kernel.org/patch/10686061/
>>
>
> Yes, that would be great and easier to understand than my patch on top 
> of yours.
>
> Additionally, can you remove the "Error:" as Will requested as part of 
> the squash?

Thanks for your consent. I have reworked the patch today, and have 
addressed Will's
comment. I will give a try on the board and post it by tomorrow.

Best regards
Vivek

>
> Thank you!
>
> Thor
>
>> Best regards
>> Vivek
>>>
>>> Will
>>
>>
>