Re: [PATCH v5 10/10] drm/fb_helper: Support framebuffers in I/O memory

[Daniel Vetter <daniel@xxxxxxxx>]

On Thu, Oct 22, 2020 at 10:37:56AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> On 22.10.20 10:05, Daniel Vetter wrote:
> > On Tue, Oct 20, 2020 at 02:20:46PM +0200, Thomas Zimmermann wrote:
> >> At least sparc64 requires I/O-specific access to framebuffers. This
> >> patch updates the fbdev console accordingly.
> >>
> >> For drivers with direct access to the framebuffer memory, the callback
> >> functions in struct fb_ops test for the type of memory and call the rsp
> >> fb_sys_ of fb_cfb_ functions. Read and write operations are implemented
> >> internally by DRM's fbdev helper.
> >>
> >> For drivers that employ a shadow buffer, fbdev's blit function retrieves
> >> the framebuffer address as struct dma_buf_map, and uses dma_buf_map
> >> interfaces to access the buffer.
> >>
> >> The bochs driver on sparc64 uses a workaround to flag the framebuffer as
> >> I/O memory and avoid a HW exception. With the introduction of struct
> >> dma_buf_map, this is not required any longer. The patch removes the rsp
> >> code from both, bochs and fbdev.
> >>
> >> v5:
> >>    * implement fb_read/fb_write internally (Daniel, Sam)
> >> v4:
> >>    * move dma_buf_map changes into separate patch (Daniel)
> >>    * TODO list: comment on fbdev updates (Daniel)
> >>
> >> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> >> Tested-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
> >> ---
> >>  Documentation/gpu/todo.rst        |  19 ++-
> >>  drivers/gpu/drm/bochs/bochs_kms.c |   1 -
> >>  drivers/gpu/drm/drm_fb_helper.c   | 227 ++++++++++++++++++++++++++++--
> >>  include/drm/drm_mode_config.h     |  12 --
> >>  4 files changed, 230 insertions(+), 29 deletions(-)
> >>
> >> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> >> index 7e6fc3c04add..638b7f704339 100644
> >> --- a/Documentation/gpu/todo.rst
> >> +++ b/Documentation/gpu/todo.rst
> >> @@ -197,13 +197,28 @@ Convert drivers to use drm_fbdev_generic_setup()
> >>  ------------------------------------------------
> >>  
> >>  Most drivers can use drm_fbdev_generic_setup(). Driver have to implement
> >> -atomic modesetting and GEM vmap support. Current generic fbdev emulation
> >> -expects the framebuffer in system memory (or system-like memory).
> >> +atomic modesetting and GEM vmap support. Historically, generic fbdev 
> >> emulation
> >> +expected the framebuffer in system memory or system-like memory. By 
> >> employing
> >> +struct dma_buf_map, drivers with frambuffers in I/O memory can be 
> >> supported
> >> +as well.
> >>  
> >>  Contact: Maintainer of the driver you plan to convert
> >>  
> >>  Level: Intermediate
> >>  
> >> +Reimplement functions in drm_fbdev_fb_ops without fbdev
> >> +-------------------------------------------------------
> >> +
> >> +A number of callback functions in drm_fbdev_fb_ops could benefit from
> >> +being rewritten without dependencies on the fbdev module. Some of the
> >> +helpers could further benefit from using struct dma_buf_map instead of
> >> +raw pointers.
> >> +
> >> +Contact: Thomas Zimmermann <tzimmermann@xxxxxxx>, Daniel Vetter
> >> +
> >> +Level: Advanced
> >> +
> >> +
> >>  drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup
> >>  -----------------------------------------------------------------
> >>  
> >> diff --git a/drivers/gpu/drm/bochs/bochs_kms.c 
> >> b/drivers/gpu/drm/bochs/bochs_kms.c
> >> index 13d0d04c4457..853081d186d5 100644
> >> --- a/drivers/gpu/drm/bochs/bochs_kms.c
> >> +++ b/drivers/gpu/drm/bochs/bochs_kms.c
> >> @@ -151,7 +151,6 @@ int bochs_kms_init(struct bochs_device *bochs)
> >>    bochs->dev->mode_config.preferred_depth = 24;
> >>    bochs->dev->mode_config.prefer_shadow = 0;
> >>    bochs->dev->mode_config.prefer_shadow_fbdev = 1;
> >> -  bochs->dev->mode_config.fbdev_use_iomem = true;
> >>    bochs->dev->mode_config.quirk_addfb_prefer_host_byte_order = true;
> >>  
> >>    bochs->dev->mode_config.funcs = &bochs_mode_funcs;
> >> diff --git a/drivers/gpu/drm/drm_fb_helper.c 
> >> b/drivers/gpu/drm/drm_fb_helper.c
> >> index 6212cd7cde1d..1d3180841778 100644
> >> --- a/drivers/gpu/drm/drm_fb_helper.c
> >> +++ b/drivers/gpu/drm/drm_fb_helper.c
> >> @@ -372,24 +372,22 @@ static void drm_fb_helper_resume_worker(struct 
> >> work_struct *work)
> >>  }
> >>  
> >>  static void drm_fb_helper_dirty_blit_real(struct drm_fb_helper *fb_helper,
> >> -                                    struct drm_clip_rect *clip)
> >> +                                    struct drm_clip_rect *clip,
> >> +                                    struct dma_buf_map *dst)
> >>  {
> >>    struct drm_framebuffer *fb = fb_helper->fb;
> >>    unsigned int cpp = fb->format->cpp[0];
> >>    size_t offset = clip->y1 * fb->pitches[0] + clip->x1 * cpp;
> >>    void *src = fb_helper->fbdev->screen_buffer + offset;
> >> -  void *dst = fb_helper->buffer->map.vaddr + offset;
> >>    size_t len = (clip->x2 - clip->x1) * cpp;
> >>    unsigned int y;
> >>  
> >> -  for (y = clip->y1; y < clip->y2; y++) {
> >> -          if (!fb_helper->dev->mode_config.fbdev_use_iomem)
> >> -                  memcpy(dst, src, len);
> >> -          else
> >> -                  memcpy_toio((void __iomem *)dst, src, len);
> >> +  dma_buf_map_incr(dst, offset); /* go to first pixel within clip rect */
> >>  
> >> +  for (y = clip->y1; y < clip->y2; y++) {
> >> +          dma_buf_map_memcpy_to(dst, src, len);
> >> +          dma_buf_map_incr(dst, fb->pitches[0]);
> >>            src += fb->pitches[0];
> >> -          dst += fb->pitches[0];
> >>    }
> >>  }
> >>  
> >> @@ -417,8 +415,9 @@ static void drm_fb_helper_dirty_work(struct 
> >> work_struct *work)
> >>                    ret = drm_client_buffer_vmap(helper->buffer, &map);
> >>                    if (ret)
> >>                            return;
> >> -                  drm_fb_helper_dirty_blit_real(helper, &clip_copy);
> >> +                  drm_fb_helper_dirty_blit_real(helper, &clip_copy, &map);
> >>            }
> >> +
> >>            if (helper->fb->funcs->dirty)
> >>                    helper->fb->funcs->dirty(helper->fb, NULL, 0, 0,
> >>                                             &clip_copy, 1);
> >> @@ -2027,6 +2026,206 @@ static int drm_fbdev_fb_mmap(struct fb_info *info, 
> >> struct vm_area_struct *vma)
> >>            return -ENODEV;
> >>  }
> >>  
> >> +static bool drm_fbdev_use_iomem(struct fb_info *info)
> >> +{
> >> +  struct drm_fb_helper *fb_helper = info->par;
> >> +  struct drm_client_buffer *buffer = fb_helper->buffer;
> >> +
> >> +  return !drm_fbdev_use_shadow_fb(fb_helper) && buffer->map.is_iomem;
> >> +}
> >> +
> >> +static ssize_t fb_read_screen_base(struct fb_info *info, char __user 
> >> *buf, size_t count, 
> >> +                             loff_t pos)
> >> +{
> >> +  const char __iomem *src = info->screen_base + pos;
> > 
> > Maybe a bit much a bikeshed, but I'd write this in terms of drm objects,
> > like the dirty_blit function, using the dma_buf_map (instead of the
> > fb_info parameter). And then instead of
> > screen_base and screen_buffer suffixes give them _mem and _iomem suffixes.
> 
> Screen_buffer can be a shadow buffer. Until the blit worker (see
> drm_fb_helper_dirty_work() ) completes, it might be more up to date than
> the real buffer that's stored in the client.
> 
> The orignal fbdev code supported an fb_sync callback to synchronize with
> outstanding screen updates (e.g., HW blit ops), but fb_sync is just
> overhead here. Copying from screen_buffer or screen_base always returns
> the most up-to-date image.
> 
> > 
> > Same for write below. Or I'm not quite understanding why we do it like
> > this here - I don't think this code will be used outside of the generic
> > fbdev code, so we can always assume that drm_fb_helper->buffer is set up.
> 
> It's similar as in the read case. If we write to the client's buffer, an
> outstanding blit worker could write the now-outdated shadow buffer over
> the user's newly written framebuffer data.
> 
> Thinking about it, we might want to schedule the blit worker at the end
> of each fb_write, so that the data makes it into the HW buffer in time.

Hm ok, makes some sense. I think there's some potential for cleanup if we
add a dma_buf_map drm_fb_helper->uapi_map which points at the right thing
always. That could then also the drm_fbdev_use_iomem() helper and make
this all look really neat.

But maybe a follow up clean up patch, if you're bored. As-is:

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

While looking at this I also noticed a potential small issue in an earlier
patch.

> > The other thing I think we need is some minimal testcases to make sure.
> > The fbtest tool used way back seems to have disappeared, I couldn't find
> > a copy of the source anywhere anymore.
> 
> As discussed on IRC, I'll add some testcase to the igt test. I'll share
> the link here when done.
> 
> Best regards
> Thomas
> 
> > 
> > With all that: Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > 
> > Cheers, Daniel
> > 
> >> +  size_t alloc_size = min(count, PAGE_SIZE);
> >> +  ssize_t ret = 0;
> >> +  char *tmp;
> >> +
> >> +  tmp = kmalloc(alloc_size, GFP_KERNEL);
> >> +  if (!tmp)
> >> +          return -ENOMEM;
> >> +
> >> +  while (count) {
> >> +          size_t c = min(count, alloc_size);
> >> +
> >> +          memcpy_fromio(tmp, src, c);
> >> +          if (copy_to_user(buf, tmp, c)) {
> >> +                  ret = -EFAULT;
> >> +                  break;
> >> +          }
> >> +
> >> +          src += c;
> >> +          buf += c;
> >> +          ret += c;
> >> +          count -= c;
> >> +  }
> >> +
> >> +  kfree(tmp);
> >> +
> >> +  return ret;
> >> +}
> >> +
> >> +static ssize_t fb_read_screen_buffer(struct fb_info *info, char __user 
> >> *buf, size_t count,
> >> +                               loff_t pos)
> >> +{
> >> +  const char *src = info->screen_buffer + pos;
> >> +
> >> +  if (copy_to_user(buf, src, count))
> >> +          return -EFAULT;
> >> +
> >> +  return count;
> >> +}
> >> +
> >> +static ssize_t drm_fbdev_fb_read(struct fb_info *info, char __user *buf,
> >> +                           size_t count, loff_t *ppos)
> >> +{
> >> +  loff_t pos = *ppos;
> >> +  size_t total_size;
> >> +  ssize_t ret;
> >> +
> >> +  if (info->state != FBINFO_STATE_RUNNING)
> >> +          return -EPERM;
> >> +
> >> +  if (info->screen_size)
> >> +          total_size = info->screen_size;
> >> +  else
> >> +          total_size = info->fix.smem_len;
> >> +
> >> +  if (pos >= total_size)
> >> +          return 0;
> >> +  if (count >= total_size)
> >> +          count = total_size;
> >> +  if (total_size - count < pos)
> >> +          count = total_size - pos;
> >> +
> >> +  if (drm_fbdev_use_iomem(info))
> >> +          ret = fb_read_screen_base(info, buf, count, pos);
> >> +  else
> >> +          ret = fb_read_screen_buffer(info, buf, count, pos);
> >> +
> >> +  if (ret > 0)
> >> +          *ppos = ret;
> >> +
> >> +  return ret;
> >> +}
> >> +
> >> +static ssize_t fb_write_screen_base(struct fb_info *info, const char 
> >> __user *buf, size_t count,
> >> +                              loff_t pos)
> >> +{
> >> +  char __iomem *dst = info->screen_base + pos;
> >> +  size_t alloc_size = min(count, PAGE_SIZE);
> >> +  ssize_t ret = 0;
> >> +  u8 *tmp;
> >> +
> >> +  tmp = kmalloc(alloc_size, GFP_KERNEL);
> >> +  if (!tmp)
> >> +          return -ENOMEM;
> >> +
> >> +  while (count) {
> >> +          size_t c = min(count, alloc_size);
> >> +
> >> +          if (copy_from_user(tmp, buf, c)) {
> >> +                  ret = -EFAULT;
> >> +                  break;
> >> +          }
> >> +          memcpy_toio(dst, tmp, c);
> >> +
> >> +          dst += c;
> >> +          buf += c;
> >> +          ret += c;
> >> +          count -= c;
> >> +  }
> >> +
> >> +  kfree(tmp);
> >> +
> >> +  return ret;
> >> +}
> >> +
> >> +static ssize_t fb_write_screen_buffer(struct fb_info *info, const char 
> >> __user *buf, size_t count,
> >> +                                loff_t pos)
> >> +{
> >> +  char *dst = info->screen_buffer + pos;
> >> +
> >> +  if (copy_from_user(dst, buf, count))
> >> +          return -EFAULT;
> >> +
> >> +  return count;
> >> +}
> >> +
> >> +static ssize_t drm_fbdev_fb_write(struct fb_info *info, const char __user 
> >> *buf,
> >> +                            size_t count, loff_t *ppos)
> >> +{
> >> +  loff_t pos = *ppos;
> >> +  size_t total_size;
> >> +  ssize_t ret;
> >> +  int err;
> >> +
> >> +  if (info->state != FBINFO_STATE_RUNNING)
> >> +          return -EPERM;
> >> +
> >> +  if (info->screen_size)
> >> +          total_size = info->screen_size;
> >> +  else
> >> +          total_size = info->fix.smem_len;
> >> +
> >> +  if (pos > total_size)
> >> +          return -EFBIG;
> >> +  if (count > total_size) {
> >> +          err = -EFBIG;
> >> +          count = total_size;
> >> +  }
> >> +  if (total_size - count < pos) {
> >> +          if (!err)
> >> +                  err = -ENOSPC;
> >> +          count = total_size - pos;
> >> +  }
> >> +
> >> +  /*
> >> +   * Copy to framebuffer even if we already logged an error. Emulates
> >> +   * the behavior of the original fbdev implementation.
> >> +   */
> >> +  if (drm_fbdev_use_iomem(info))
> >> +          ret = fb_write_screen_base(info, buf, count, pos);
> >> +  else
> >> +          ret = fb_write_screen_buffer(info, buf, count, pos);
> >> +
> >> +  if (ret > 0)
> >> +          *ppos = ret;
> >> +
> >> +  if (err)
> >> +          return err;
> >> +
> >> +  return ret;
> >> +}
> >> +
> >> +static void drm_fbdev_fb_fillrect(struct fb_info *info,
> >> +                            const struct fb_fillrect *rect)
> >> +{
> >> +  if (drm_fbdev_use_iomem(info))
> >> +          drm_fb_helper_cfb_fillrect(info, rect);
> >> +  else
> >> +          drm_fb_helper_sys_fillrect(info, rect);
> >> +}
> >> +
> >> +static void drm_fbdev_fb_copyarea(struct fb_info *info,
> >> +                            const struct fb_copyarea *area)
> >> +{
> >> +  if (drm_fbdev_use_iomem(info))
> >> +          drm_fb_helper_cfb_copyarea(info, area);
> >> +  else
> >> +          drm_fb_helper_sys_copyarea(info, area);
> >> +}
> >> +
> >> +static void drm_fbdev_fb_imageblit(struct fb_info *info,
> >> +                             const struct fb_image *image)
> >> +{
> >> +  if (drm_fbdev_use_iomem(info))
> >> +          drm_fb_helper_cfb_imageblit(info, image);
> >> +  else
> >> +          drm_fb_helper_sys_imageblit(info, image);
> >> +}
> >> +
> >>  static const struct fb_ops drm_fbdev_fb_ops = {
> >>    .owner          = THIS_MODULE,
> >>    DRM_FB_HELPER_DEFAULT_OPS,
> >> @@ -2034,11 +2233,11 @@ static const struct fb_ops drm_fbdev_fb_ops = {
> >>    .fb_release     = drm_fbdev_fb_release,
> >>    .fb_destroy     = drm_fbdev_fb_destroy,
> >>    .fb_mmap        = drm_fbdev_fb_mmap,
> >> -  .fb_read        = drm_fb_helper_sys_read,
> >> -  .fb_write       = drm_fb_helper_sys_write,
> >> -  .fb_fillrect    = drm_fb_helper_sys_fillrect,
> >> -  .fb_copyarea    = drm_fb_helper_sys_copyarea,
> >> -  .fb_imageblit   = drm_fb_helper_sys_imageblit,
> >> +  .fb_read        = drm_fbdev_fb_read,
> >> +  .fb_write       = drm_fbdev_fb_write,
> >> +  .fb_fillrect    = drm_fbdev_fb_fillrect,
> >> +  .fb_copyarea    = drm_fbdev_fb_copyarea,
> >> +  .fb_imageblit   = drm_fbdev_fb_imageblit,
> >>  };
> >>  
> >>  static struct fb_deferred_io drm_fbdev_defio = {
> >> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> >> index 5ffbb4ed5b35..ab424ddd7665 100644
> >> --- a/include/drm/drm_mode_config.h
> >> +++ b/include/drm/drm_mode_config.h
> >> @@ -877,18 +877,6 @@ struct drm_mode_config {
> >>     */
> >>    bool prefer_shadow_fbdev;
> >>  
> >> -  /**
> >> -   * @fbdev_use_iomem:
> >> -   *
> >> -   * Set to true if framebuffer reside in iomem.
> >> -   * When set to true memcpy_toio() is used when copying the framebuffer 
> >> in
> >> -   * drm_fb_helper.drm_fb_helper_dirty_blit_real().
> >> -   *
> >> -   * FIXME: This should be replaced with a per-mapping is_iomem
> >> -   * flag (like ttm does), and then used everywhere in fbdev code.
> >> -   */
> >> -  bool fbdev_use_iomem;
> >> -
> >>    /**
> >>     * @quirk_addfb_prefer_xbgr_30bpp:
> >>     *
> >> -- 
> >> 2.28.0
> >>
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch