From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x226WL7uDS6SzrRi6X+lLRD3/11WSBY6WxUcANHGmdZsgcwuJKanVdVcqi3H9GlkD+vUQVUPF ARC-Seal: i=1; a=rsa-sha256; t=1517410075; cv=none; d=google.com; s=arc-20160816; b=ILvf89vovNFgaCT4TW8NpB4nsOWBpe8kf2f/N5e6EYGm57tHKvOJM26V4j9Ed/TS0j o7wxVHF2ztCwbsHB1q7HK+YpZQnpao2CycWNyn4tRdvvuiwGgTHo5xhbokiIwLc7k6nI P0nVYfuJXupjh9o0dPY2/yljON8WTiw91CBL6xpfANyJ9vD2x84RjbfACJIpc4/aNyMs FOJW9jp+JJyYFjJxcuJrDWJSmuekGnAXrvNcROJuaUzP9pSXdO4uSsNmhLrVwZcF33eV AE4NYLuxYuzxXRE0mStvakVzSc332DeJzgG8DvGkr93YZn5V3NFWl6Vv5gKc29eeZ25V 9c1A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:arc-authentication-results; bh=FmfWqkMV5hS4OQRiqdSH2XaXg2tyi8sc5RnTDYXiCy0=; b=V9dweZpe2/75VdQ1/5Nta8Q0+f+/QiK6wXb1bvrrfvDV/otgp4qThWxyPyNcDoQnqK lOi9++ViePqdXyo7MWQX8gR8H95Z5oeoACKWFb3IsOeZ+cd862fdLQgoEBValO41P8hm YtCj9aqqHCBa5DgsA4RVFeNTqdZJs1xwPFh1gSj2osOJbFFvr6xgOQPM9trqVEZ2YYll 3mCQWghc5517agYQTYxjtrostcfysmdqg0ZFNPqI9U8QTqI83oJkaHa1C6SGrLhSvkgV 0zK/saQ5xSM+BCKKjbzyY8h7hTUDS3L4Exu8tA9fL1DowZ1zzokM/d+qvNQbNGzB5ryK bKxQ== ARC-Authentication-Results: i=1; mx.google.com; spf=neutral (google.com: 80.229.23.120 is neither permitted nor denied by best guess record for domain of liviu@dudau.co.uk) smtp.mailfrom=liviu@dudau.co.uk Authentication-Results: mx.google.com; spf=neutral (google.com: 80.229.23.120 is neither permitted nor denied by best guess record for domain of liviu@dudau.co.uk) smtp.mailfrom=liviu@dudau.co.uk Date: Wed, 31 Jan 2018 14:47:53 +0000 From: Liviu Dudau To: Maxime Ripard Cc: Yong , kbuild test robot , kbuild-all@01.org, Mauro Carvalho Chehab , Rob Herring , Mark Rutland , Chen-Yu Tsai , "David S. Miller" , Greg Kroah-Hartman , Hans Verkuil , Linus Walleij , Randy Dunlap , Stanimir Varbanov , Hugues Fruchet , Yannick Fertre , Philipp Zabel , Arnd Bergmann , Benjamin Gaignard , Ramesh Shanmugasundaram , Sakari Ailus , Rick Chang , linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com, megous@megous.com Subject: Re: [linux-sunxi] Re: [PATCH v6 2/2] media: V3s: Add support for Allwinner CSI. Message-ID: <20180131144753.GB19945@bart.dudau.co.uk> References: <1516695531-23349-1-git-send-email-yong.deng@magewell.com> <201801260759.RyNhDZz4%fengguang.wu@intel.com> <20180126094658.aa70ed3f890464f6051e21e4@magewell.com> <20180126110041.f89848325b9ecfb07df387ca@magewell.com> <20180131030807.GA19945@bart.dudau.co.uk> <20180131074212.7hvb3nqkt22h2chg@flea.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180131074212.7hvb3nqkt22h2chg@flea.lan> User-Agent: Mutt/1.5.24 (2015-08-30) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590370608168306586?= X-GMAIL-MSGID: =?utf-8?q?1591119787317751059?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Jan 31, 2018 at 08:42:12AM +0100, Maxime Ripard wrote: > Hi Liviu, Hi Maxime, > > On Wed, Jan 31, 2018 at 03:08:08AM +0000, Liviu Dudau wrote: > > On Fri, Jan 26, 2018 at 11:00:41AM +0800, Yong wrote: > > > Hi Maxime, > > > > > > On Fri, 26 Jan 2018 09:46:58 +0800 > > > Yong wrote: > > > > > > > Hi Maxime, > > > > > > > > Do you have any experience in solving this problem? > > > > It seems the PHYS_OFFSET maybe undeclared when the ARCH is not arm. > > > > > > Got it. > > > Should I add 'depends on ARM' in Kconfig? > > > > No, I don't think you should do that, you should fix the code. > > > > The dma_addr_t addr that you've got is ideally coming from dma_alloc_coherent(), > > in which case the addr is already "suitable" for use by the device (because the > > bus where the device is attached to does all the address translations). > > Like we're discussing in that other part of the thread with Thierry > and Arnd, things are slightly more complicated than that :) Yeah, sorry, my threading of the discussion was broken and I've seen the rest of the thread after I have replied. My bad! > > In our case, the bus where the device is attached will not do the > address translations, and shouldn't. In my view, the bus is already doing address translation at physical level, AFAIU it remaps the memory to zero. What you (we?) need is a simple bus driver that registers the correct virt_to_bus()/bus_to_virt() hooks for the device that do this translation at the DMA API level as well. > > > If you apply PHYS_OFFSET forcefully to it you might get unexpected > > results. > > Out of curiosity, what would be these unexpected results? If in the future (or a parallel world setup) the device is sitting behind an IOMMU, the addr value might well be smaller than PHYS_OFFSET and you will under-wrap, possibly starting to hit kernel physical addresses (or anything sitting at the top of the physical memory). >>From my time playing with IOMMUs and PCI domains, I've learned to treat the dma_addr_t as a cookie value and never try to do arithmetics with it. Best regards, Liviu > > Thanks! > Maxime > > -- > Maxime Ripard, Free Electrons > Embedded Linux and Kernel engineering > http://free-electrons.com > > -- > You received this message because you are subscribed to the Google Groups "linux-sunxi" group. > To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscribe@googlegroups.com. > For more options, visit https://groups.google.com/d/optout.