linux-kernel - Re: [PATCH v8 5/6] iommu/arm-smmu: Add support for qcom,smmu-v2 variant

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Date:   Tue, 13 Feb 2018 17:57:39 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>
Cc:     "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <joro@...tes.org>,
        Mark Rutland <mark.rutland@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        Rob Clark <robdclark@...il.com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Greg KH <gregkh@...uxfoundation.org>, sboyd@...eaurora.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v8 5/6] iommu/arm-smmu: Add support for qcom,smmu-v2 variant

Hi Vivek,

Thanks for the patch. Please see my comments inline.

On Fri, Feb 9, 2018 at 7:57 PM, Vivek Gautam
<vivek.gautam@...eaurora.org> wrote:
> qcom,smmu-v2 is an arm,smmu-v2 implementation with specific
> clock and power requirements. This smmu core is used with
> multiple masters on msm8996, viz. mdss, video, etc.
> Add bindings for the same.
>
> Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
> Reviewed-by: Rob Herring <robh@...nel.org>
> ---
>
> Changes in v8:
>  - Added the missing IOMMU_OF_DECLARE declaration for "qcom,smmu-v2"
>
>  .../devicetree/bindings/iommu/arm,smmu.txt         | 43 ++++++++++++++++++++++
>  drivers/iommu/arm-smmu.c                           | 14 +++++++
>  2 files changed, 57 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> index 8a6ffce12af5..169222ae2706 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> @@ -17,10 +17,19 @@ conditions.
>                          "arm,mmu-401"
>                          "arm,mmu-500"
>                          "cavium,smmu-v2"
> +                        "qcom,<soc>-smmu-v2", "qcom,smmu-v2"
>
>                    depending on the particular implementation and/or the
>                    version of the architecture implemented.
>
> +                  A number of Qcom SoCs use qcom,smmu-v2 version of the IP.
> +                  "qcom,<soc>-smmu-v2" represents a soc specific compatible
> +                  string that should be present along with the "qcom,smmu-v2"
> +                  to facilitate SoC specific clocks/power connections and to
> +                  address specific bug fixes.
> +                  An example string would be -
> +                  "qcom,msm8996-smmu-v2", "qcom,smmu-v2".

Hmm, I remember that for <soc> and similar wildcards we required
explicitly listing allowed values. Rob, has it changed since I
stumbled upon such thing last time (or I just got it wrong before)?

> +
>  - reg           : Base address and size of the SMMU.
>
>  - #global-interrupts : The number of global interrupts exposed by the
> @@ -71,6 +80,23 @@ conditions.
>                    or using stream matching with #iommu-cells = <2>, and
>                    may be ignored if present in such cases.
>
> +- clock-names:    Should be "bus", and "iface" for "qcom,smmu-v2"
> +                  implementation.
> +
> +                  "bus" clock for "qcom,smmu-v2" is required for downstream
> +                  bus access and for the smmu ptw.
> +
> +                  "iface" clock is required to access smmu's registers through
> +                  the TCU's programming interface.

nit: Could we have it in a bit more structured way? E.g.

- clock-names: List of names of clocks input to the device. The
required list depends on particular implementation and is as follows:
 - for "qcom,smmu-v2":
   - "bus": clock required for downstream bus access and for the smmu ptw,
   - "iface":  clock required to access smmu's registers through the
TCU's programming interface.
 - unspecified for other implementations.

(+/- wrapping)

> +
> +- clocks:         Phandles for respective clocks described by clock-names.

Phandle is just a pointer to another node. Clocks are however
specified using a phandle and a number of arguments, depending on the
clock controller. I'd change it to:

- clocks:         Specifiers for all clocks listed in the clock-names
property, as per generic clock bindings.

> +
> +- power-domains:  Phandles to SMMU's power domain specifier. This is
> +                  required even if SMMU belongs to the master's power
> +                  domain, as the SMMU will have to be enabled and
> +                  accessed before master gets enabled and linked to its
> +                  SMMU.

>From DT point of view, the relationship of SMMU belonging to a master
device doesn't exist. The power-domains property needs to be properly
specified for all devices within power domains represented in DT, with
an exception of the case when the parent-child relationship is
explicitly stated in DT by child devices being represented by child
nodes of the parent device node.

- power-domains: Specifiers for power domains required to be powered
on for the SMMU to operate, as per generic power domain bindings.

Best regards,
Tomasz