From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 93772C4741F for ; Sat, 26 Sep 2020 07:18:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 585D1206E5 for ; Sat, 26 Sep 2020 07:18:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728680AbgIZHS5 (ORCPT ); Sat, 26 Sep 2020 03:18:57 -0400 Received: from asavdk3.altibox.net ([109.247.116.14]:50996 "EHLO asavdk3.altibox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726149AbgIZHS5 (ORCPT ); Sat, 26 Sep 2020 03:18:57 -0400 X-Greylist: delayed 311 seconds by postgrey-1.27 at vger.kernel.org; Sat, 26 Sep 2020 03:18:55 EDT Received: from ravnborg.org (unknown [188.228.123.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by asavdk3.altibox.net (Postfix) with ESMTPS id 25FB6200E6; Sat, 26 Sep 2020 09:13:35 +0200 (CEST) Date: Sat, 26 Sep 2020 09:13:34 +0200 From: Sam Ravnborg To: Thomas Zimmermann Cc: sumit.semwal@linaro.org, christian.koenig@amd.com, afd@ti.com, corbet@lwn.net, benjamin.gaignard@linaro.org, lmark@codeaurora.org, labbott@redhat.com, Brian.Starkey@arm.com, john.stultz@linaro.org, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@linux.ie, daniel@ffwll.ch, l.stach@pengutronix.de, linux+etnaviv@armlinux.org.uk, christian.gmeiner@gmail.com, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, thierry.reding@gmail.com, jonathanh@nvidia.com, pawel@osciak.com, m.szyprowski@samsung.com, kyungmin.park@samsung.com, tfiga@chromium.org, mchehab@kernel.org, matthew.auld@intel.com, robin.murphy@arm.com, thomas.hellstrom@intel.com, kraxel@redhat.com, arnd@arndb.de, gregkh@linuxfoundation.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-doc@vger.kernel.org, etnaviv@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-tegra@vger.kernel.org Subject: Re: [PATCH v3 0/4] dma-buf: Flag vmap'ed memory as system or I/O memory Message-ID: <20200926071334.GA42915@ravnborg.org> References: <20200925115601.23955-1-tzimmermann@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200925115601.23955-1-tzimmermann@suse.de> X-CMAE-Score: 0 X-CMAE-Analysis: v=2.3 cv=CaYmGojl c=1 sm=1 tr=0 a=S6zTFyMACwkrwXSdXUNehg==:117 a=S6zTFyMACwkrwXSdXUNehg==:17 a=kj9zAlcOel0A:10 a=VwQbUJbxAAAA:8 a=7gkXJVJtAAAA:8 a=VHCyA-Zl7a4LrUxzt10A:9 a=MWUCcgKsKLDUXRMs:21 a=VnMhorO1uwyDQjeY:21 a=CjuIK1q_8ugA:10 a=AjGcO6oz07-iQ99wixmX:22 a=E9Po1WZjFZOl8hwRPBS3:22 Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Thomas. Sorry for chiming in late here, have been offline for a while. On Fri, Sep 25, 2020 at 01:55:57PM +0200, Thomas Zimmermann wrote: > Dma-buf provides vmap() and vunmap() for retriving and releasing mappings > of dma-buf memory in kernel address space. The functions operate with plain > addresses and the assumption is that the memory can be accessed with load > and store operations. This is not the case on some architectures (e.g., > sparc64) where I/O memory can only be accessed with dedicated instructions. > > This patchset introduces struct dma_buf_map, which contains the address of > a buffer and a flag that tells whether system- or I/O-memory instructions > are required. The whole idea with a struct that can represent both a pointer to system memory and io memory is very nice. dma-buf is one user of this but we may/will see other users. So the naming seems of as this should be a concept independent of dma-buf. And then the struct definition and all the helpers should be moved away from dma-buf. Maybe something like this: struct simap { union { void __iomem *vaddr_iomem; void *vaddr; }; bool is_iomem; }; Where simap is a shorthand for system_iomem_map And it could al be stuffed into a include/linux/simap.h file. Not totally sold on the simap name - but wanted to come up with something. With this approach users do not have to pull in dma-buf to use it and users will not confuse that this is only for dma-buf usage. I am sorry for being late with the feedback. Sam > Some background: updating the DRM framebuffer console on sparc64 makes the > kernel panic. This is because the framebuffer memory cannot be accessed with > system-memory instructions. We currently employ a workaround in DRM to > address this specific problem. [1] > > To resolve the problem, we'd like to address it at the most common point, > which is the dma-buf framework. The dma-buf mapping ideally knows if I/O > instructions are required and exports this information to it's users. The > new structure struct dma_buf_map stores the buffer address and a flag that > signals I/O memory. Affected users of the buffer (e.g., drivers, frameworks) > can then access the memory accordingly. > > This patchset only introduces struct dma_buf_map, and updates struct dma_buf > and it's interfaces. Further patches can update dma-buf users. For example, > there's a prototype patchset for DRM that fixes the framebuffer problem. [2] > > Further work: TTM, one of DRM's memory managers, already exports an > is_iomem flag of its own. It could later be switched over to exporting struct > dma_buf_map, thus simplifying some code. Several DRM drivers expect their > fbdev console to operate on I/O memory. These could possibly be switched over > to the generic fbdev emulation, as soon as the generic code uses struct > dma_buf_map. > > v3: > * update fastrpc driver (kernel test robot) > * expand documentation (Daniel) > * move documentation into separate patch > v2: > * always clear map parameter in dma_buf_vmap() (Daniel) > * include dma-buf-heaps and i915 selftests (kernel test robot) > * initialize cma_obj before using it in drm_gem_cma_free_object() > (kernel test robot) > > [1] https://lore.kernel.org/dri-devel/20200725191012.GA434957@ravnborg.org/ > [2] https://lore.kernel.org/dri-devel/20200806085239.4606-1-tzimmermann@suse.de/ > > Thomas Zimmermann (4): > dma-buf: Add struct dma-buf-map for storing struct dma_buf.vaddr_ptr > dma-buf: Use struct dma_buf_map in dma_buf_vmap() interfaces > dma-buf: Use struct dma_buf_map in dma_buf_vunmap() interfaces > dma-buf: Document struct dma_buf_map > > Documentation/driver-api/dma-buf.rst | 9 + > drivers/dma-buf/dma-buf.c | 42 ++-- > drivers/dma-buf/heaps/heap-helpers.c | 10 +- > drivers/gpu/drm/drm_gem_cma_helper.c | 20 +- > drivers/gpu/drm/drm_gem_shmem_helper.c | 17 +- > drivers/gpu/drm/drm_prime.c | 15 +- > drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 13 +- > drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 13 +- > .../drm/i915/gem/selftests/i915_gem_dmabuf.c | 18 +- > .../gpu/drm/i915/gem/selftests/mock_dmabuf.c | 14 +- > drivers/gpu/drm/tegra/gem.c | 23 ++- > .../common/videobuf2/videobuf2-dma-contig.c | 17 +- > .../media/common/videobuf2/videobuf2-dma-sg.c | 19 +- > .../common/videobuf2/videobuf2-vmalloc.c | 21 +- > drivers/misc/fastrpc.c | 6 +- > include/drm/drm_prime.h | 5 +- > include/linux/dma-buf-map.h | 193 ++++++++++++++++++ > include/linux/dma-buf.h | 11 +- > 18 files changed, 372 insertions(+), 94 deletions(-) > create mode 100644 include/linux/dma-buf-map.h > > -- > 2.28.0