From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: Usage of _PAGE_PCD et al in i915 driver Date: Thu, 14 Aug 2014 05:55:11 +0200 Message-ID: <53EC331F.3000508@suse.com> References: <53E4B338.3040904@suse.com> <20140813080705.31a0901a@jbarnes-desktop> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140813080705.31a0901a@jbarnes-desktop> Sender: linux-kernel-owner@vger.kernel.org To: Jesse Barnes , Daniel Vetter Cc: Ben Widawsky , Linux Kernel Mailing List , intel-gfx List-Id: intel-gfx@lists.freedesktop.org On 08/13/2014 05:07 PM, Jesse Barnes wrote: > On Fri, 8 Aug 2014 15:14:15 +0200 > Daniel Vetter wrote: > >> Adding relevant mailing lists. >> >> On Fri, Aug 8, 2014 at 1:23 PM, Juergen Gross wrote: >>> I'm just about to create a patch for full PAT support in the Linux >>> kernel, including Xen. For this purpose I introduce a translation >>> between cache modes and pte bits. >>> >>> Scanning the kernel sources for usage of the cache mode bits in the >>> pte I discovered drivers/gpu/drm/i915/i915_gem_gtt.h is using >>> _PAGE_PCD, _PAGE_PWT and _PAGE_PAT. I think those defines are used >>> to create ptes not for usage by the main processor, but for the >>> graphics processor. Is this true? In this case I'd suggest to define >>> i915-specific macros instead of using the x86 ones. >> >> Yeah, those are gpu specific PAT tables, but the hw engineers >> specifically designed this to match, and we've tried to follow the cpu >> side to match it. Especially in the future that will be somewhat >> important, since we want to fully share the entire address space >> between cpu and gpu on the next platform. Jesse is working on that. > > Right, we have an x86 compatible MMU in the GPU itself, so re-using the > defines makes sense. I suppose with your work you'll move them and > make them a bit more opaque? If so, we'll still want a way to get at > them directly, or access your mapping functions for generating PTE bits > for the GPU MMU. Using the mapping functions I'm introducing should work, if the MMU has an x86 compatible MSR_IA32_CR_PAT which is configured the same way as on the x86 processor (be aware that Xen is using another MSR_IA32_CR_PAT setting as the Linux kernel). Juergen