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Message-ID: <20160427064317.GA4225@vireshk-i7>
Date: Wed, 27 Apr 2016 12:13:17 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Viresh Kumar <vireshk@...nel.org>,
Vinod Koul <vinod.koul@...el.com>,
linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
Rob Herring <robh+dt@...nel.org>,
Mark Brown <broonie@...nel.org>,
Vineet Gupta <vgupta@...opsys.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v6 2/4] dmaengine: dw: revisit data_width property
On 25-04-16, 15:35, Andy Shevchenko wrote:
> There are several changes are done here:
>
> - Convert the property to be in bytes
>
> Besides this is common practice for such property the use of a value in bytes
> much more convenient than handling the encoded value.
>
> - Rename data_width to data-width in the device tree bindings
>
> - While here, replace dwc_fast_ffs() by __ffs()
>
> The change leaves the support for old format as well just in case someone will
> use a newer kernel with an old device tree blob.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> Documentation/devicetree/bindings/dma/snps-dma.txt | 6 ++--
> arch/arc/boot/dts/abilis_tb10x.dtsi | 2 +-
> arch/arm/boot/dts/spear13xx.dtsi | 4 +--
> drivers/dma/dw/core.c | 42 ++++++----------------
> drivers/dma/dw/platform.c | 5 ++-
> include/linux/platform_data/dma-dw.h | 2 +-
> 6 files changed, 21 insertions(+), 40 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/dma/snps-dma.txt b/Documentation/devicetree/bindings/dma/snps-dma.txt
> index c99c1ff..544b9b9 100644
> --- a/Documentation/devicetree/bindings/dma/snps-dma.txt
> +++ b/Documentation/devicetree/bindings/dma/snps-dma.txt
> @@ -13,8 +13,8 @@ Required properties:
> - chan_priority: priority of channels. 0 (default): increase from chan 0->n, 1:
> increase from chan n->0
> - block_size: Maximum block size supported by the controller
> -- data_width: Maximum data width supported by hardware per AHB master
> - (0 - 8bits, 1 - 16bits, ..., 5 - 256bits)
> +- data-width: Maximum data width supported by hardware per AHB master
> + (in bytes, power of 2)
>
>
> Optional properties:
> @@ -38,7 +38,7 @@ Example:
> chan_allocation_order = <1>;
> chan_priority = <1>;
> block_size = <0xfff>;
> - data_width = <3 3>;
> + data-width = <8 8>;
> };
You broke backward compatibility with earlier DTs.
What's backward compatibility ?
Consider that the DT from an earlier version of kernel is part of the bootrom of
a SoC. Now that bootrom should work just fine with any new kernel version. i.e.
old DT + new kernels should always work.
--
viresh
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