From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v3 4/7] of: configure the platform device dma parameters Date: Tue, 06 May 2014 11:40:38 +0200 Message-ID: <7182186.5Q53eQg77F@wuerfel> References: <1398353407-2345-1-git-send-email-santosh.shilimkar@ti.com> <536806F4.1090904@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <536806F4.1090904@ti.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Santosh Shilimkar Cc: "devicetree@vger.kernel.org" , Grygorii Strashko , Russell King , Greg Kroah-Hartman , Linus Walleij , "linux-kernel@vger.kernel.org" , Grant Likely , Rob Herring , Catalin Marinas , Olof Johansson , "linux-arm-kernel@lists.infradead.org" List-Id: devicetree@vger.kernel.org On Monday 05 May 2014 17:47:32 Santosh Shilimkar wrote: > + dev->coherent_dma_mask = DMA_BIT_MASK(32); > + if (!dev->dma_mask) > + dev->dma_mask = &dev->coherent_dma_mask; > + > + /* > + * if dma-ranges property doesn't exist - just return else > + * setup the dma offset > + */ > + ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size); > + if (ret < 0) { > + dev_dbg(dev, "no dma range information to setup\n"); > + return; > + } > + > + /* DMA ranges found. Calculate and set dma_pfn_offset */ > + dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr); > + dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset); > +} I think there should at least be a comment about why we are computing the correct DMA mask here and then ignore that and just use DMA_BIT_MASK(32) instead. I understand that Russell and Rob prefer it that way and I'm not going to argue, but I find it counterintuitive and I think it deserves an explanation in the source code for anybody who is trying to figure out how things fit together. Arnd