Hi Miquel, > -----Original Message----- > From: Miquel Raynal [mailto:miquel.ray...@bootlin.com] > Sent: Tuesday, August 21, 2018 3:23 PM > To: Naga Sureshkumar Relli <nagas...@xilinx.com> > Cc: Boris Brezillon <boris.brezil...@bootlin.com>; rich...@nod.at; > dw...@infradead.org; > computersforpe...@gmail.com; marek.va...@gmail.com; kyungmin.p...@samsung.com; > abs...@codeaurora.org; peterpand...@micron.com; frieder.schre...@exceet.de; > linux- > m...@lists.infradead.org; linux-kernel@vger.kernel.org; Michal Simek > <mich...@xilinx.com>; > nagasureshkumarre...@gmail.com > Subject: Re: [LINUX PATCH v10 1/2] dt-bindings: mtd: arasan: Add device tree > binding > documentation > > Hi Naga, > > Naga Sureshkumar Relli <nagas...@xilinx.com> wrote on Tue, 21 Aug 2018 > 09:22:07 +0000: > > > Hi Boris, > > > > > -----Original Message----- > > > From: Boris Brezillon [mailto:boris.brezil...@bootlin.com] > > > Sent: Tuesday, August 21, 2018 11:30 AM > > > To: Naga Sureshkumar Relli <nagas...@xilinx.com> > > > Cc: miquel.ray...@bootlin.com; rich...@nod.at; dw...@infradead.org; > > > computersforpe...@gmail.com; marek.va...@gmail.com; > > > kyungmin.p...@samsung.com; abs...@codeaurora.org; > > > peterpand...@micron.com; frieder.schre...@exceet.de; linux- > > > m...@lists.infradead.org; linux-kernel@vger.kernel.org; Michal Simek > > > <mich...@xilinx.com>; nagasureshkumarre...@gmail.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 <nagas...@xilinx.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.
Thanks, Naga Sureshkumar Relli. > > Miquèl
