From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 2/2] of: Restrict DMA configuration Date: Fri, 11 Aug 2017 20:01:06 +0200 Message-ID: <20170811180106.GB1921@lst.de> References: <0819179085df6c41c70e83a2c5c138b95c0386b3.1502468875.git.robin.murphy@arm.com> <82633e62b64e28dc18bc466319065b92faf2414f.1502468875.git.robin.murphy@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <82633e62b64e28dc18bc466319065b92faf2414f.1502468875.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Robin Murphy Cc: robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org, m.szyprowski-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org, stefan.wahren-eS4NqCHxEME@public.gmane.org, afaerber-l3A5Bk7waGM@public.gmane.org, hverkuil-qWit8jRvyhVmR6Xm/wNWPw@public.gmane.org, johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org List-Id: devicetree@vger.kernel.org On Fri, Aug 11, 2017 at 05:29:57PM +0100, Robin Murphy wrote: > The good news is that DT already gives us the ammunition to do the right > thing - anything lacking a "dma-ranges" property should be considered > not to have a mapping of DMA address space from its children to its > parent, thus anything for which of_dma_get_range() does not succeed does > not need DMA configuration. That sounds like a good heuristic. At least in theory apparently :( > The bad news is that strictly enforcing that would likely break just > about every FDT platform out there, since most authors have either not > considered the property at all or have mistakenly assumed that omitting > "dma-ranges" is equivalent to including the empty property. Thus we have > little choice but to special-case platform, AMBA and PCI devices so they > continue to receive configuration unconditionally as before. At least > anything new will have to get it right in future... That still sounds like a useful compromise. > ret = of_dma_get_range(np, &dma_addr, &paddr, &size); > if (ret < 0) { > + /* > + * For legacy reasons, we have to assume some devices need > + * DMA configuration regardless of whether "dma-ranges" is > + * correctly specified or not. > + */ > + if (!dev_is_pci(dev) && > +#ifdef CONFIG_ARM_AMBA > + dev->bus != &amba_bustype && > +#endif > + dev->bus != &platform_bus_type) > + return ret == -ENODEV ? 0 : ret; > + It would be really nice to have dev_is_amba and dev_is_plaform helpers to reduce the ifdef mess. But it should be okay even without that cleanup. > + if (!size) > + size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1); I find this way to deal with an overflow really odd, but given that it's just moved around I'm not going to complain. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html