Re: [PATCH v4 01/16] dt-bindings: mtd: gpmc-onenand: Update properties description

[Sebastian Reichel <sre@kernel.org>]

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Hi,

On Wed, Nov 15, 2017 at 04:12:06PM +0100, Ladislav Michl wrote:
> On Wed, Nov 15, 2017 at 02:43:39PM +0100, Sebastian Reichel wrote:
> > Hi,
> > 
> > On Sat, Nov 11, 2017 at 10:16:56PM +0100, Ladislav Michl wrote:
> > > Compatible property is required for OMAP2+ mtd driver. Also
> > > add R/B pin gpio description and delete unused dma-channel
> > > property.
> > > 
> > > Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
> > > ---
> > >  Changes:
> > >  -v4: new patch
> > > 
> > >  Documentation/devicetree/bindings/mtd/gpmc-onenand.txt | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/mtd/gpmc-onenand.txt b/Documentation/devicetree/bindings/mtd/gpmc-onenand.txt
> > > index b6e8bfd024f4..9d7b1409deab 100644
> > > --- a/Documentation/devicetree/bindings/mtd/gpmc-onenand.txt
> > > +++ b/Documentation/devicetree/bindings/mtd/gpmc-onenand.txt
> > > @@ -9,13 +9,14 @@ Documentation/devicetree/bindings/memory-controllers/omap-gpmc.txt
> > >  
> > >  Required properties:
> > >  
> > > + - compatible:		"ti,omap2-onenand"
> > 
> > I suggest to also add more specific compatible values (i.e.
> > "ti,omap3-onenand") in case it is needed later. They don't
> > hurt much and may prevent ugly hacks in the future.
> 
> We tried hard to avoid anything omap3 specific (it was present in earlier
> versions of this patchset). And NAND driver is also okay with "ti,omap3-nand"
> (I know it is a poor argument). So far all OMAP2/3 differences seems to come
> from both devices unavailable to the person who did the code change.
> 
> While I agree it is in general good idea, I have personal problem with that
> as there are devices in field with "ti,omap2-onenand" compatible and OMAP3530.
> 
> See this function:
> http://git.denx.de/?p=u-boot.git;a=blob;f=board/isee/igep00x0/igep00x0.c;h=5c7f2567118a1e17bdb6f76f29a7161628776bf7;hb=HEAD#l158
> Board comes either with NAND or OneNAND, bootloader detects that and
> enables proper node. Updating bootloader is potentially dangerous, so I'd
> like to avoid that.
> 
> However, if you insist on idea above, I'm okay with keeping some of tree
> patches for a while...

The best practice for DT bindings is to have a specific compatible
and a generic fallback. Something like

compatible = "ti,omap3-onenand", "ti,omap2-onenand";

You can just ignore the "ti,omap3-onenand" in the driver for now.
Just add it to the bindings and the DTS files. Then it is there in
case it is needed at some point.

-- Sebastian

> > >   - reg:			The CS line the peripheral is connected to
> > > - - gpmc,device-width	Width of the ONENAND device connected to the GPMC
> > > + - gpmc,device-width:	Width of the ONENAND device connected to the GPMC
> > >  			in bytes. Must be 1 or 2.
> > >  
> > >  Optional properties:
> > >  
> > > - - dma-channel:		DMA Channel index
> > > + - rb-gpios:		GPIO specifier for the ready/busy# pin.
> > >  
> > >  For inline partition table parsing (optional):
> > >  
> > > @@ -35,6 +36,7 @@ Example for an OMAP3430 board:
> > >  		#size-cells = <1>;
> > >  
> > >  		onenand@0 {
> > > +			compatible = "ti,omap2-onenand";
> > >  			reg = <0 0 0>; /* CS0, offset 0 */
> > >  			gpmc,device-width = <2>;
> > >  
> > 
> > -- Sebastian
> 
> 
> --
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