From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Wilson Subject: Re: [PATCH 13/18] drm/i915: Introduce i915_gem_object_create_stolen() Date: Mon, 05 Nov 2012 16:59:44 +0000 Message-ID: References: <1350666204-8101-1-git-send-email-chris@chris-wilson.co.uk> <1350666204-8101-13-git-send-email-chris@chris-wilson.co.uk> <20121105163226.4a38c7c7@bwidawsk.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by gabe.freedesktop.org (Postfix) with ESMTP id 80DDEA0259 for ; Mon, 5 Nov 2012 09:00:35 -0800 (PST) In-Reply-To: <20121105163226.4a38c7c7@bwidawsk.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Ben Widawsky Cc: intel-gfx@lists.freedesktop.org List-Id: intel-gfx@lists.freedesktop.org On Mon, 5 Nov 2012 16:32:26 +0000, Ben Widawsky wrote: > On Fri, 19 Oct 2012 18:03:19 +0100 > Chris Wilson wrote: > > > Allow for the creation of GEM objects backed by stolen memory. As these > > are not backed by ordinary pages, we create a fake dma mapping and store > > the address in the scatterlist rather than obj->pages. > > > > v2: Mark _i915_gem_object_create_stolen() as static, as noticed by Jesse > > Barnes. > > > > Signed-off-by: Chris Wilson > > Reviewed-by: Jesse Barnes > > Deferring on an r-b for now until I understand the point of most of this > patch. The stolen support is a precursor for fastboot, where we need to wrap the allocations made by the BIOS from the stolen memory and reuse that for our own framebuffers. > > + struct scatterlist *sg; > > + > > BUG_ON(offset + size <= dev_priv->mm.gtt->stolen_size); Done with a minor amendment. > > + /* We hide that we have no struct page backing our stolen object > > + * by wrapping the contiguous physical allocation with a fake > > + * dma mapping in a single scatterlist. > > + */ > > + > > + st = kmalloc(sizeof(*st), GFP_KERNEL); > > + if (st == NULL) > > + return NULL; > > + > > + if (!sg_alloc_table(st, 1, GFP_KERNEL)) { Fixed. > > + kfree(st); > > + return NULL; > > + } > > + > > + sg = st->sgl; > > + sg->offset = offset; > > + sg->length = size; > > + > > + sg_dma_address(sg) = dev_priv->mm.stolen_base + offset; > > + sg_dma_len(sg) = size; > > + > > Do we want to make stolen_base a dma_addr_t (or at least typecast it)? Interesting enough, the current FBC registers are limited to only using 32bit addresses, so stolen_base atm is not technically a dma_addr_t. Maybe I'm picking hairs. :) > > + return st; > > +} > > + > > +static int i915_gem_object_get_pages_stolen(struct drm_i915_gem_object *obj) > > +{ > > + BUG(); > > + return -EINVAL; > > +} > > + > > __noreturn, or maybe just make .get_pages = NULL, and do the check in > the upper layer get_pages? I refer you to http://lwn.net/Articles/336262/ where the argument is put forth that default no-op functions are preferrable in most cases to interpretting special NULL vfuncs. We have adopted this elsewhere in i915.ko to good effect. > > + stolen = drm_mm_search_free(&dev_priv->mm.stolen, size, 4096, 0); > > + if (stolen) > > + stolen = drm_mm_get_block(stolen, size, 4096); > > + if (stolen == NULL) > > + return NULL; > > Could probably do slightly better here with ERR_PTR(-ENOMEM) but since > we don't do that elsewhere, I guess it doesn't matter. I was tempted - it would have just looked odd as being the only create routine to do so. :) -Chris -- Chris Wilson, Intel Open Source Technology Centre