linux-kernel - Re: [PATCH v4 06/20] dt-bindings: memory: tegra: Squash tegra20-gart into tegra20-mc

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Date:   Mon, 24 Sep 2018 11:55:30 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/20] dt-bindings: memory: tegra: Squash tegra20-gart
 into tegra20-mc

On Mon, Sep 24, 2018 at 03:41:39AM +0300, Dmitry Osipenko wrote:
> Splitting GART and Memory Controller wasn't a good decision that was made
> back in the day. Given that the GART driver wasn't ever been used by
> anything in the kernel, we decided that it will be better to correct the
> mistakes of the past and merge two bindings into a single one. As a result
> there is a DT ABI change for the Memory Controller that allows not to
> break newer kernels using older DT and not to break older kernels using
> newer DT, that is done by changing the 'compatible' of the node to
> 'tegra20-mc-gart' and adding a new-required clock property. The new clock
> property also puts the tegra20-mc binding in line with the bindings of the
> later Tegra generations.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  .../bindings/iommu/nvidia,tegra20-gart.txt    | 14 ----------
>  .../memory-controllers/nvidia,tegra20-mc.txt  | 27 +++++++++++++------
>  2 files changed, 19 insertions(+), 22 deletions(-)
>  delete mode 100644 Documentation/devicetree/bindings/iommu/nvidia,tegra20-gart.txt
> 
> diff --git a/Documentation/devicetree/bindings/iommu/nvidia,tegra20-gart.txt b/Documentation/devicetree/bindings/iommu/nvidia,tegra20-gart.txt
> deleted file mode 100644
> index 099d9362ebc1..000000000000
> --- a/Documentation/devicetree/bindings/iommu/nvidia,tegra20-gart.txt
> +++ /dev/null
> @@ -1,14 +0,0 @@
> -NVIDIA Tegra 20 GART
> -
> -Required properties:
> -- compatible: "nvidia,tegra20-gart"
> -- reg: Two pairs of cells specifying the physical address and size of
> -  the memory controller registers and the GART aperture respectively.
> -
> -Example:
> -
> -	gart {
> -		compatible = "nvidia,tegra20-gart";
> -		reg = <0x7000f024 0x00000018	/* controller registers */
> -		       0x58000000 0x02000000>;	/* GART aperture */
> -	};
> diff --git a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-mc.txt b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-mc.txt
> index 7d60a50a4fa1..e55328237df4 100644
> --- a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-mc.txt
> +++ b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-mc.txt
> @@ -1,26 +1,37 @@
>  NVIDIA Tegra20 MC(Memory Controller)
>  
>  Required properties:
> -- compatible : "nvidia,tegra20-mc"
> -- reg : Should contain 2 register ranges(address and length); see the
> -  example below. Note that the MC registers are interleaved with the
> -  GART registers, and hence must be represented as multiple ranges.
> +- compatible : "nvidia,tegra20-mc-gart"
> +- reg : Should contain 2 register ranges: physical base address and length of
> +  the controller's registers and the GART aperture respectively.

Couldn't we have achieved the same thing by adding a reg-names property
instead of using a different compatible string? After all we only change
what information the DT provides, but the device is still a "tegra20-mc"
device.

Thierry

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