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Date: Tue, 21 Aug 2018 12:52:48 +0200 From: Boris Brezillon <boris.brezillon@...tlin.com> To: Naga Sureshkumar Relli <nagasure@...inx.com> Cc: Miquel Raynal <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 10:44:54 +0000 Naga Sureshkumar Relli <nagasure@...inx.com> wrote: > Hi Miquel, > > > -----Original Message----- > > From: Miquel Raynal [mailto:miquel.raynal@...tlin.com] > > Sent: Tuesday, August 21, 2018 3:23 PM > > To: Naga Sureshkumar Relli <nagasure@...inx.com> > > Cc: Boris Brezillon <boris.brezillon@...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 > > > > 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. > UBIFS uses vmalloc'ed buffers whereas for DMA it should be DMA-able, i.e uses physically contiguous memory. > Hence we used a DT property to make it work in PIO mode. > Some discussion happened in https://patchwork.kernel.org/patch/9675007/. > But whatever I said above, is with older arasan_nand driver, now anyway we have > virt_addr_valid(). By checking this we can use DMA or PIO. > This is the information I have, but I may be wrong. My recommandation: set the NAND_USE_BOUNCE_BUFFER and always use DMA.
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