Re: [PATCH v2] drm/vgem: implement virtual GEM

[Ben Widawsky <ben@bwidawsk.net>]

On Sat, Jan 31, 2015 at 11:02:05AM -0500, Rob Clark wrote:
> On Fri, Jan 30, 2015 at 1:05 PM, Zach Reizner <zachr@google.com> wrote:
> > This patch implements the virtual GEM driver with PRIME sharing which
> > allows vgem to import a gem object from other drivers for the purpose
> > of mmap-ing them to userspace. The mmap is done using the mmap
> > operation exported by other drivers.
> >
> > v2: remove platform_device and do not attach to dma bufs
> >
> > Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
> > Signed-off-by: Adam Jackson <ajax@redhat.com>
> > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > Signed-off-by: Zach Reizner <zachr@google.com>
> 
> couple small suggestions/comments below, but with those addressed,
> 
> Reviewed-by: Rob Clark <robdclark@gmail.com>
> 
> > ---
> >  drivers/gpu/drm/Kconfig             |   9 +
> >  drivers/gpu/drm/Makefile            |   1 +
> >  drivers/gpu/drm/vgem/Makefile       |   4 +
> >  drivers/gpu/drm/vgem/vgem_dma_buf.c |  96 +++++++++
> >  drivers/gpu/drm/vgem/vgem_drv.c     | 390 ++++++++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/vgem/vgem_drv.h     |  57 ++++++
> >  6 files changed, 557 insertions(+)
> >  create mode 100644 drivers/gpu/drm/vgem/Makefile
> >  create mode 100644 drivers/gpu/drm/vgem/vgem_dma_buf.c
> >  create mode 100644 drivers/gpu/drm/vgem/vgem_drv.c
> >  create mode 100644 drivers/gpu/drm/vgem/vgem_drv.h
> >
> 
> [snip]
> 
> > diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> > new file mode 100644
> > index 0000000..e20f4a4
> > --- /dev/null
> > +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> > @@ -0,0 +1,390 @@
> > +/*
> > + * Copyright 2011 Red Hat, Inc.
> > + * Copyright © 2014 The Chromium OS Authors
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a
> > + * copy of this software and associated documentation files (the "Software")
> > + * to deal in the software without restriction, including without limitation
> > + * on the rights to use, copy, modify, merge, publish, distribute, sub
> > + * license, and/or sell copies of the Software, and to permit persons to whom
> > + * them Software is furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice (including the next
> > + * paragraph) shall be included in all copies or substantial portions of the
> > + * Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTIBILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.  IN NO EVENT SHALL
> > + * THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES, OR OTHER LIABILITY, WHETHER
> > + * IN AN ACTION OF CONTRACT, TORT, OR OTHERWISE, ARISING FROM, OUT OF OR IN
> > + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
> > + *
> > + * Authors:
> > + *     Adam Jackson <ajax@redhat.com>
> > + *     Ben Widawsky <ben@bwidawsk.net>
> > + */
> > +
> > +/**
> > + * This is vgem, a (non-hardware-backed) GEM service.  This is used by Mesa's
> > + * software renderer and the X server for efficient buffer sharing.
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/ramfs.h>
> > +#include <linux/shmem_fs.h>
> > +#include <linux/dma-buf.h>
> > +#include "vgem_drv.h"
> > +
> > +#define DRIVER_NAME    "vgem"
> > +#define DRIVER_DESC    "Virtual GEM provider"
> > +#define DRIVER_DATE    "20120112"
> > +#define DRIVER_MAJOR   1
> > +#define DRIVER_MINOR   0
> > +
> > +void vgem_gem_put_pages(struct drm_vgem_gem_object *obj)
> > +{
> > +       int num_pages = obj->base.size / PAGE_SIZE;
> > +       int i;
> > +
> > +       for (i = 0; i < num_pages; i++) {
> > +               if (obj->pages[i] == NULL)
> > +                       break;
> 
> seems like other than this break statement, you could use
> drm_gem_put_pages()..  not entirely sure why you'd encounter a null
> page, but if there is a legit reason for that, then just add the check
> in drm_gem_put_pages() (plus maybe a comment) and use that..
> 

First, this code predated drm_gem_put_pages, so it was probably just an
oversight that a consolidated function existed. As for the NULL, it's because
the cleanup of failed vgem get_pages() just calls vgem put_pages() (you can't
have sparsely populated entries, but the last n pointers can be NULL). If the
helpers just dtrt, then it should use that.

> > +               page_cache_release(obj->pages[i]);
> > +       }
> > +
> > +       drm_free_large(obj->pages);
> > +       obj->pages = NULL;
> > +}
> > +
> > +static void vgem_gem_free_object(struct drm_gem_object *obj)
> > +{
> > +       struct drm_vgem_gem_object *vgem_obj = to_vgem_bo(obj);
> > +
> > +       drm_gem_free_mmap_offset(obj);
> > +
> > +       if (vgem_obj->use_dma_buf && obj->dma_buf) {
> > +               dma_buf_put(obj->dma_buf);
> > +               obj->dma_buf = NULL;
> > +       }
> > +
> > +       drm_gem_object_release(obj);
> > +
> > +       if (vgem_obj->pages)
> > +               vgem_gem_put_pages(vgem_obj);
> > +
> > +       vgem_obj->pages = NULL;
> > +
> > +       kfree(vgem_obj);
> > +}
> > +
> > +int vgem_gem_get_pages(struct drm_vgem_gem_object *obj)
> > +{
> > +       struct address_space *mapping;
> > +       gfp_t gfpmask = GFP_KERNEL;
> > +       int num_pages, i, ret = 0;
> > +
> > +       if (obj->pages || obj->use_dma_buf)
> > +               return 0;
> > +
> > +       num_pages = obj->base.size / PAGE_SIZE;
> > +       obj->pages = drm_malloc_ab(num_pages, sizeof(struct page *));
> > +       if (obj->pages == NULL)
> > +               return -ENOMEM;
> > +
> > +       mapping = obj->base.filp->f_path.dentry->d_inode->i_mapping;
> 
> again, seems like you could use drm_gem_get_pages().. although you get
> the mapping in a slightly different way.. not sure if that was
> intentional?
> 

Again, this predates the helpers :D My original patches on top of ajax were from
Feb. 2012. Helpers seem like the right thing to do now.

> BR,
> -R
> 
> > +       gfpmask |= mapping_gfp_mask(mapping);
> > +
> > +       for (i = 0; i < num_pages; i++) {
> > +               struct page *page;
> > +               obj->pages[i] = NULL;
> > +               page = shmem_read_mapping_page_gfp(mapping, i, gfpmask);
> > +               if (IS_ERR(page)) {
> > +                       ret = PTR_ERR(page);
> > +                       goto err_out;
> > +               }
> > +               obj->pages[i] = page;
> > +       }
> > +
> > +       return ret;
> > +
> > +err_out:
> > +       vgem_gem_put_pages(obj);
> > +       return ret;
> > +}
> > +
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