From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Zhang Subject: Re: First version of host1x intro Date: Thu, 06 Dec 2012 16:13:33 +0800 Message-ID: <50C053AD.2000802@gmail.com> References: <50BF1831.3060606@nvidia.com> <50C0440D.3000702@gmail.com> <1354778441.1503.92.camel@tellur> <50C04E1D.1050702@gmail.com> <1354780836.1503.102.camel@tellur> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1354780836.1503.102.camel@tellur> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lucas Stach Cc: =?UTF-8?B?VGVyamUgQmVyZ3N0csO2bQ==?= , "dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Thierry Reding List-Id: linux-tegra@vger.kernel.org On 12/06/2012 04:00 PM, Lucas Stach wrote: > Am Donnerstag, den 06.12.2012, 15:49 +0800 schrieb Mark Zhang: [...] >> >> OK. So these relocation addresses are used to let userspace tells kernel >> which buffers mentioned in the command should be relocated to addresses >> which host1x clients able to reach. >> > Yep, preferably all buffers referenced by a command stream should > already be set up in such a position (CMA with Tegra2) or the relocation > should be nothing more than setting up IOMMU page tables (Tegra3). > >> I'm also wondering that, if our driver understands the stuffs in the >> commands, maybe we can find out all addresses in the command, in that >> way, we will not need userspace tells us which are the addresses need to >> be relocated, right? > > No. How will the kernel ever know which buffer gets referenced in a > command stream? All the kernel sees is is a command stream with > something like "blit data to address 0xADDR" in it. The only info that > you can gather from that is that there must be some buffer to blit into. > Neither do you know which buffer the stuff should be going to, nor can > you know if you blit to offset zero in this buffer. It's perfectly valid > to only use a subregion of a buffer. > > Or maybe I'm misunderstanding you and you mean it the other way around. > You don't let userspace dictate the addresses, the relocation > information just tells the kernel to find the addresses of the > referenced buffers for you and insert them, instead of the dummy > information, into the command stream. Yes, I think this is what I mean. No dummy information in the command stream, userspace just fills the address which it uses(actually this is cpu address of the buffer) in the command stream, and our driver must have a HashTable or something which contains the buffer address pair -- (cpu address, dma address), so our driver can find the dma addresses for every buffer then modify the addresses in the command stream. Hope I explain that clear. > > Regards, > Lucas > >