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

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Date:   Mon, 26 Nov 2018 16:25:35 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Will Deacon <will.deacon@....com>, thor.thayer@...ux.intel.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>,
        iommu@...ts.linux-foundation.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


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/

Best regards
Vivek
>
> Will