From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: Tegra DRM device tree bindings Date: Wed, 27 Jun 2012 12:02:46 -0600 Message-ID: <4FEB4AC6.2060909@wwwdotorg.org> References: <20120626105513.GA9552@avionic-0098.mockup.avionic-design.de> <20120626160224.40ba10a26e3dd3a56b1f312c@nvidia.com> <20120626140033.GC1115@avionic-0098.mockup.avionic-design.de> <20120627154400.d9d7db67128404079d98ab39@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120627154400.d9d7db67128404079d98ab39-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Hiroshi Doyu Cc: "devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org" , Thierry Reding , "dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-tegra@vger.kernel.org On 06/27/2012 06:44 AM, Hiroshi Doyu wrote: ... > I think that there are 2 cases: > > (1) discontiguous memory with IOMMU > (2) contiguous memory without IOMMU(called "carveout" in general?) ... > For (2), although memory is mostly anonymous one, we may need to know > how much to allocate, where we only need "size". This size is not from > h/w feature, but it depends on the system load/usage. So I think that > this size can be passed from kernel command line? For exmaple, we can > specify how much contiguous memory is necessary with putting > "coherent_pool=??M" in the kernel command line as below: > > coherent_pool=nn[KMG] [ARM,KNL] > Sets the size of memory pool for coherent, atomic dma > allocations. I guess if that's the standard way of initializing CMA, then that's fine. It'd be nice if there was a way to specify that from the DT too; that way the user/distro/bootloader constructing the kernel command-line wouldn't have to remember to add "random" (potentially Tegra-/board-specific) extra arguments onto the command-line; the Tegra command-line in the upstream kernel is quite clean right now, especially compare to the enormous number of options we require downstream:-(