linux-kernel - Re: [PATCH v6 1/2] mtd: arasan: Add device tree binding documentation

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Date:   Mon, 5 Dec 2016 09:36:30 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     Punnaiah Choudary Kalluri <punnaiah.choudary.kalluri@...inx.com>,
        dwmw2@...radead.org, computersforpeace@...il.com, richard@....at,
        cyrille.pitchen@...el.com, robh+dt@...nel.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        michals@...inx.com, kalluripunnaiahchoudary@...il.com,
        kpc528@...il.com, Punnaiah Choudary Kalluri <punnaia@...inx.com>
Subject: Re: [PATCH v6 1/2] mtd: arasan: Add device tree binding
 documentation

On Mon, 5 Dec 2016 05:25:54 +0100
Marek Vasut <marek.vasut@...il.com> wrote:

> On 12/05/2016 05:11 AM, Punnaiah Choudary Kalluri wrote:
> > This patch adds the dts binding document for arasan nand flash
> > controller.
> > 
> > Signed-off-by: Punnaiah Choudary Kalluri <punnaia@...inx.com>
> > Acked-by: Rob Herring <robh@...nel.org>
> > ---
> > changes in v6:
> > - Removed num-cs property
> > - Separated nandchip from nand controller
> > changes in v5:
> > - None
> > Changes in v4:
> > - Added num-cs property
> > - Added clock support
> > Changes in v3:
> > - None
> > Changes in v2:
> > - None
> > ---
> >  .../devicetree/bindings/mtd/arasan_nfc.txt         | 38 ++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/mtd/arasan_nfc.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/mtd/arasan_nfc.txt b/Documentation/devicetree/bindings/mtd/arasan_nfc.txt
> > new file mode 100644
> > index 0000000..dcbe7ad
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/mtd/arasan_nfc.txt
> > @@ -0,0 +1,38 @@
> > +Arasan Nand Flash Controller with ONFI 3.1 support  
> 
> Arasan NAND Flash ...
> 
> > +Required properties:
> > +- compatible: Should be "arasan,nfc-v3p10"  
> 
> This v3p10 looks like version 3 patchlevel 10, but shouldn't we have
> some fallback option which doesn't encode IP version in the compat
> string ?

Not necessarily. Usually you define a generic compatible when you have
other reliable means to detect the IP version (a version register for
example).
If you can't detect that at runtime, then providing only specific
compatible strings is a good solution to avoid breaking the DT ABI.

> 
> Also, shouldn't quirks be handled by DT props instead of effectively
> encoding them into the compatible string ?

Well, from my experience, it's better to hide as much as possible
behind the compatible. This way, if new quirks are needed for a
specific revision, you can update the driver without having to change
the DT.

> 
> > +- reg: Memory map for module access
> > +- interrupt-parent: Interrupt controller the interrupt is routed through
> > +- interrupts: Should contain the interrupt for the device
> > +- clock-name: List of input clocks - "clk_sys", "clk_flash"
> > +	      (See clock bindings for details)
> > +- clocks: Clock phandles (see clock bindings for details)
> > +
> > +Optional properties:
> > +- arasan,has-mdma: Enables Dma support  
> 
> 'Enables DMA support' , with DMA in caps.
> 
> > +for nand partition information please refer the below file  
> 
> For NAND ...
> 
> > +Documentation/devicetree/bindings/mtd/partition.txt
> > +
> > +Example:
> > +	nand0: nand@...00000 {
> > +		compatible = "arasan,nfc-v3p10"
> > +		reg = <0x0 0xff100000 0x1000>;
> > +		clock-name = "clk_sys", "clk_flash"
> > +		clocks = <&misc_clk &misc_clk>;
> > +		interrupt-parent = <&gic>;
> > +		interrupts = <0 14 4>;
> > +		arasan,has-mdma;
> > +		#address-cells = <1>;
> > +		#size-cells = <0>
> > +
> > +		nand@0 {
> > +			reg = <0>
> > +			partition@0 {
> > +				label = "filesystem";
> > +				reg = <0x0 0x0 0x1000000>;
> > +			};
> > +			(...)
> > +		};
> > +	};
> >   
> 
>