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Message-ID: <20180821115238.1ad4dcb8@xps13>
Date: Tue, 21 Aug 2018 11:52:38 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Naga Sureshkumar Relli <nagasure@...inx.com>
Cc: Boris Brezillon <boris.brezillon@...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
Hi Naga,
Naga Sureshkumar Relli <nagasure@...inx.com> wrote on Tue, 21 Aug 2018
09:22:07 +0000:
> Hi Boris,
>
> > -----Original Message-----
> > From: Boris Brezillon [mailto:boris.brezillon@...tlin.com]
> > Sent: Tuesday, August 21, 2018 11:30 AM
> > To: Naga Sureshkumar Relli <nagasure@...inx.com>
> > Cc: miquel.raynal@...tlin.com; richard@....at; dwmw2@...radead.org;
> > computersforpeace@...il.com; marek.vasut@...il.com; kyungmin.park@...sung.com;
> > absahu@...eaurora.org; peterpandong@...ron.com; frieder.schrempf@...eet.de; linux-
> > mtd@...ts.infradead.org; linux-kernel@...r.kernel.org; Michal Simek <michals@...inx.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?
> Actually we put these compatible strings based on the comments on v7 series.
> Anyway I will just keep "xlnx,zynqmp-nand" as compatible.
> >
> > > > > +
> > > > > +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.
> UBIFS doesn't work with DMA, hence we are using a DT property to operate the driver in IO.
> But as you pointed (use virt_is_valid()), with this we can switch our driver to operate in PIO or DMA.
> I will remove this from DT.
I don't get why UBIFS would not work with DMA? This is a significant
drawback.
Miquèl
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