Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935221AbcCPP1k (ORCPT ); Wed, 16 Mar 2016 11:27:40 -0400 Received: from mail-wm0-f42.google.com ([74.125.82.42]:33194 "EHLO mail-wm0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935092AbcCPP1j (ORCPT ); Wed, 16 Mar 2016 11:27:39 -0400 Date: Wed, 16 Mar 2016 16:28:25 +0100 From: Daniel Vetter To: Robin Murphy Cc: airlied@linux.ie, dri-devel@lists.freedesktop.org, liviu.dudau@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] drm/fb_cma_helper: Implement fb_mmap callback Message-ID: <20160316152825.GR14170@phenom.ffwll.local> Mail-Followup-To: Robin Murphy , airlied@linux.ie, dri-devel@lists.freedesktop.org, liviu.dudau@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org References: <11eb10d95109abc104beb94c0409d49644ea8517.1458140105.git.robin.murphy@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <11eb10d95109abc104beb94c0409d49644ea8517.1458140105.git.robin.murphy@arm.com> X-Operating-System: Linux phenom 4.3.0-1-amd64 User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3413 Lines: 89 On Wed, Mar 16, 2016 at 02:57:49PM +0000, Robin Murphy wrote: > In the absence of an fb_mmap callback, the fbdev code falls back to a > naive implementation which relies upon the DMA address being the same > as the physical address, and the buffer being physically contiguous > from there. Whilst this often holds for standard CMA allocations via > the platform's regular DMA ops, if the allocation is provided by an > IOMMU then such assumptions can fall apart spectacularly. > > To resolve this, reroute the fb_mmap call to the appropriate DMA API > implementation, as per the other cma_helper calls. > > Signed-off-by: Robin Murphy > --- > > Hi dri-devel, > > This is an empirical fix for something I tickled via the newly-added > ARM HDLCD driver on a Juno platform - I have no idea whatsoever about > how "proper" it is in terms of the DRM infrastructure, so feel free to > treat this as a bug report rather than an actual patch if appropriate ;) I think the best case would be if we could have a generic fbdev helper that remaps to dumb mmap support. But that's a bit tricky to pull of: 1. from fb_info we can get at the fbdev drm_framebuffer. 2. from a drm_framebuffer we can get at the underlying backing storage object using fb->funcs->get_handle. 3. With that handle we could go into the dumb mmap support (using als the vma) and create the mmap. Except that ->get_handle needs a file_priv, and that just exist for the fbdev emulation kms client. I guess we could fix that by creating a minimal fake drm file_priv for the fbdev emulation (and treat it more like any other kms client), but I think that's way too much work when this simple patch here gets the job done. Long story short, assuming this doesn't break other cma-helper using drivers: Acked-by: Daniel Vetter > > drivers/gpu/drm/drm_fb_cma_helper.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c > index bb88e3d..117d7ea 100644 > --- a/drivers/gpu/drm/drm_fb_cma_helper.c > +++ b/drivers/gpu/drm/drm_fb_cma_helper.c > @@ -23,6 +23,7 @@ > #include > #include > #include > +#include > #include > > struct drm_fb_cma { > @@ -221,6 +222,12 @@ int drm_fb_cma_debugfs_show(struct seq_file *m, void *arg) > EXPORT_SYMBOL_GPL(drm_fb_cma_debugfs_show); > #endif > > +static int drm_fb_cma_mmap(struct fb_info *info, struct vm_area_struct *vma) > +{ > + return dma_mmap_writecombine(info->device, vma, info->screen_base, > + info->fix.smem_start, info->fix.smem_len); > +} > + > static struct fb_ops drm_fbdev_cma_ops = { > .owner = THIS_MODULE, > .fb_fillrect = drm_fb_helper_sys_fillrect, > @@ -231,6 +238,7 @@ static struct fb_ops drm_fbdev_cma_ops = { > .fb_blank = drm_fb_helper_blank, > .fb_pan_display = drm_fb_helper_pan_display, > .fb_setcmap = drm_fb_helper_setcmap, > + .fb_mmap = drm_fb_cma_mmap, > }; > > static int drm_fbdev_cma_create(struct drm_fb_helper *helper, > -- > 2.7.3.dirty > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch