linux-kernel - Re: [LINUX PATCH v10 1/2] dt-bindings: mtd: arasan: Add device tree binding documentation

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Message-ID: <20180821075948.28962170@bbrezillon>
Date:   Tue, 21 Aug 2018 07:59:48 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Naga Sureshkumar Relli <nagasure@...inx.com>
Cc:     "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "richard@....at" <richard@....at>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "computersforpeace@...il.com" <computersforpeace@...il.com>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
        "absahu@...eaurora.org" <absahu@...eaurora.org>,
        "peterpandong@...ron.com" <peterpandong@...ron.com>,
        "frieder.schrempf@...eet.de" <frieder.schrempf@...eet.de>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Simek <michals@...inx.com>,
        "nagasureshkumarrelli@...il.com" <nagasureshkumarrelli@...il.com>
Subject: Re: [LINUX PATCH v10 1/2] dt-bindings: mtd: arasan: Add device tree
 binding documentation

On Tue, 21 Aug 2018 05:47:18 +0000
Naga Sureshkumar Relli <nagasure@...inx.com> wrote:

> > > +Required properties:
> > > +- compatible:		Should be "xlnx,zynqmp-nand" or "arasan,nfc-v3p10"  
> > 
> > In your example it's not an "or" since both are defined.  
> In our previous discussion (https://lore.kernel.org/patchwork/patch/748901/)
> We decided to have compatible strings like " compatible = "<soc-vendor>,<ip-revision>", "arasan,<ip-revision>";"
> So it should be either of these.
> so I will write something like below
> "Possible values are  "xlnx,zynqmp-nand" 
> 			"arasan,nfc-v3p10"
> And in example I will mention any one compatible.
> Is it ok?

Hm, why do you need arasan,nfc-v3p10 at all if it's supposed to be
overloaded by a soc specific compat?

> > > +
> > > +Optional properties:
> > > +- arasan,has-mdma: Enables DMA support  
> > 
> > Can't you detect that based on the compatible (or thanks to a register). If it's something you
> > choose when configuring the IP and can't detect at runtime I guess it's fine.  
> There is no way to select DMA when configuring the IP.
> But it has internal DMA and there is a register to select PIO or DMA while starting a transfer.
> So if user really don't want DMA, then we will never set DMA in the code based on DT property.

If it's a purely SW choice, then is shouldn't be described in the DT.
You can use a module param, but I'm not even sure why one would want to
disable DMA.