From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring Subject: Re: [PATCH 05/14] dmaengine: dma-jz4780: Add support for the JZ4740 SoC Date: Tue, 17 Jul 2018 11:40:20 -0600 Message-ID: References: <20180703123214.23090-1-paul@crapouillou.net> <20180703123214.23090-6-paul@crapouillou.net> <20180709171226.GK22377@vkoul-mobl> <20180716213339.GA19161@rob-hp-laptop> <20180717153407.GF3219@vkoul-mobl> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <20180717153407.GF3219@vkoul-mobl> Sender: linux-kernel-owner@vger.kernel.org To: Vinod Cc: Paul Cercueil , Mark Rutland , Ralf Baechle , Paul Burton , James Hogan , Zubair Lutfullah Kakakhel , Mathieu Malaterre , Daniel Silsby , "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" , devicetree@vger.kernel.org, "linux-kernel@vger.kernel.org" , Linux-MIPS List-Id: devicetree@vger.kernel.org On Tue, Jul 17, 2018 at 9:34 AM Vinod wrote: > > On 16-07-18, 15:33, Rob Herring wrote: > > On Mon, Jul 09, 2018 at 10:42:26PM +0530, Vinod wrote: > > > On 03-07-18, 14:32, Paul Cercueil wrote: > > > > > > > enum jz_version { > > > > + ID_JZ4740, > > > > ID_JZ4770, > > > > ID_JZ4780, > > > > }; > > > > @@ -247,6 +248,7 @@ static void jz4780_dma_desc_free(struct virt_dma_desc *vdesc) > > > > } > > > > > > > > static const unsigned int jz4780_dma_ord_max[] = { > > > > + [ID_JZ4740] = 5, > > > > [ID_JZ4770] = 6, > > > > [ID_JZ4780] = 7, > > > > }; > > > > @@ -801,11 +803,13 @@ static struct dma_chan *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec, > > > > } > > > > > > > > static const unsigned int jz4780_dma_nb_channels[] = { > > > > + [ID_JZ4740] = 6, > > > > [ID_JZ4770] = 6, > > > > [ID_JZ4780] = 32, > > > > }; > > > > > > I feel these should be done away with if we describe hardware in DT > > > > The compatible property can imply things like this. > > So what is the general recommendation, let DT describe hardware > including version delta or use compatible to code that in driver? Compatible is the version. Looking at the above, the version or ID isn't even stable. > Is it documented anywhere? Not really. It's a judgment call generally. Maybe # of DMA channels should be a property because that is something most controllers have. But you really have to define the property up front, not when the 2nd version of h/w shows up with different properties. To start defining guidelines, a couple of things come to mind: - Define properties for parameters that vary from board to board (for one SoC). - You can't add new required properties to existing bindings, so the not present default must work for all existing compatibles (or you need per compatible driver data). - Bugs/quirks/errata should be handled by compatible, not adding a property. Because bugs should be fixable without a dtb update and only a kernel update. Rob