Re: [PATCH v6 2/4] dmaengine: dw: revisit data_width property

[Vinod Koul]

On Wed, Apr 27, 2016 at 12:13:17PM +0530, Viresh Kumar wrote:
> 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@xxxxxxxxxxxxxxx>
> > ---
> >  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.

And this is not fixed yet!.

-- 
~Vinod