Re: [PATCH v4 10/10] drm/fb_helper: Support framebuffers in I/O memory

[Sam Ravnborg <sam@xxxxxxxxxxxx>]

Hi Thomas.

On Thu, Oct 15, 2020 at 02:38:06PM +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.
> 
> 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.
> 
> v4:
>       * move dma_buf_map changes into separate patch (Daniel)
>       * TODO list: comment on fbdev updates (Daniel)

I have been offline for a while so have not followed all the threads on
this. So may comments below may well be addressed but I failed to see
it.

If the point about fb_sync is already addressed/considered then:
Reviewed-by: Sam Ravnborg <sam@xxxxxxxxxxxx>


> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> ---
>  Documentation/gpu/todo.rst        |  19 ++-
>  drivers/gpu/drm/bochs/bochs_kms.c |   1 -
>  drivers/gpu/drm/drm_fb_helper.c   | 217 ++++++++++++++++++++++++++++--
>  include/drm/drm_mode_config.h     |  12 --
>  4 files changed, 220 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;
Good to see this workaround gone again!

> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 6212cd7cde1d..462b0c130ebb 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);
> @@ -755,6 +754,136 @@ void drm_fb_helper_sys_imageblit(struct fb_info *info,
>  }
>  EXPORT_SYMBOL(drm_fb_helper_sys_imageblit);
>  
So far everything looks good.

> +static ssize_t drm_fb_helper_cfb_read(struct fb_info *info, char __user *buf,
> +                                   size_t count, loff_t *ppos)
> +{
> +     unsigned long p = *ppos;
> +     u8 *dst;
> +     u8 __iomem *src;
> +     int c, err = 0;
> +     unsigned long total_size;
> +     unsigned long alloc_size;
> +     ssize_t ret = 0;
> +
> +     if (info->state != FBINFO_STATE_RUNNING)
> +             return -EPERM;
> +
> +     total_size = info->screen_size;
> +
> +     if (total_size == 0)
> +             total_size = info->fix.smem_len;
> +
> +     if (p >= total_size)
> +             return 0;
> +
> +     if (count >= total_size)
> +             count = total_size;
> +
> +     if (count + p > total_size)
> +             count = total_size - p;
> +
> +     src = (u8 __iomem *)(info->screen_base + p);
screen_base is a char __iomem * - so this cast looks semi redundant.

> +
> +     alloc_size = min(count, PAGE_SIZE);
> +
> +     dst = kmalloc(alloc_size, GFP_KERNEL);
> +     if (!dst)
> +             return -ENOMEM;
> +
Same comment as below about fb_sync.


> +     while (count) {
> +             c = min(count, alloc_size);
> +
> +             memcpy_fromio(dst, src, c);
> +             if (copy_to_user(buf, dst, c)) {
> +                     err = -EFAULT;
> +                     break;
> +             }
> +
> +             src += c;
> +             *ppos += c;
> +             buf += c;
> +             ret += c;
> +             count -= c;
> +     }
> +
> +     kfree(dst);
> +
> +     if (err)
> +             return err;
> +
> +     return ret;
> +}
> +
> +static ssize_t drm_fb_helper_cfb_write(struct fb_info *info, const char 
> __user *buf,
> +                                    size_t count, loff_t *ppos)
> +{
> +     unsigned long p = *ppos;
> +     u8 *src;
> +     u8 __iomem *dst;
> +     int c, err = 0;
> +     unsigned long total_size;
> +     unsigned long alloc_size;
> +     ssize_t ret = 0;
> +
> +     if (info->state != FBINFO_STATE_RUNNING)
> +             return -EPERM;
> +
> +     total_size = info->screen_size;
> +
> +     if (total_size == 0)
> +             total_size = info->fix.smem_len;
> +
> +     if (p > total_size)
> +             return -EFBIG;
> +
> +     if (count > total_size) {
> +             err = -EFBIG;
> +             count = total_size;
> +     }
> +
> +     if (count + p > total_size) {
> +             /*
> +              * The framebuffer is too small. We do the
> +              * copy operation, but return an error code
> +              * afterwards. Taken from fbdev.
> +              */
> +             if (!err)
> +                     err = -ENOSPC;
> +             count = total_size - p;
> +     }
> +
> +     alloc_size = min(count, PAGE_SIZE);
> +
> +     src = kmalloc(alloc_size, GFP_KERNEL);
> +     if (!src)
> +             return -ENOMEM;
> +
> +     dst = (u8 __iomem *)(info->screen_base + p);
> +

The fbdev variant call the fb_sync callback here.
noveau and gma500 implments the fb_sync callback - but no-one else.


> +     while (count) {
> +             c = min(count, alloc_size);
> +
> +             if (copy_from_user(src, buf, c)) {
> +                     err = -EFAULT;
> +                     break;
> +             }
> +             memcpy_toio(dst, src, c);
When we rewrite this part to use dma_buf_map_memcpy_to() then we can
merge the two variants of helper_{sys,cfb}_read()?
Which is part of the todo - so OK
> +
> +             dst += c;
> +             *ppos += c;
> +             buf += c;
> +             ret += c;
> +             count -= c;
> +     }
> +
> +     kfree(src);
> +
> +     if (err)
> +             return err;
> +
> +     return ret;
> +}
> +
>  /**
>   * drm_fb_helper_cfb_fillrect - wrapper around cfb_fillrect
>   * @info: fbdev registered by the helper
> @@ -2027,6 +2156,66 @@ static int drm_fbdev_fb_mmap(struct fb_info *info, 
> struct vm_area_struct *vma)
>               return -ENODEV;
>  }
>  
> +static ssize_t drm_fbdev_fb_read(struct fb_info *info, char __user *buf,
> +                              size_t count, loff_t *ppos)
> +{
> +     struct drm_fb_helper *fb_helper = info->par;
> +     struct drm_client_buffer *buffer = fb_helper->buffer;
> +
> +     if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> +             return drm_fb_helper_sys_read(info, buf, count, ppos);
> +     else
> +             return drm_fb_helper_cfb_read(info, buf, count, ppos);
> +}
> +
> +static ssize_t drm_fbdev_fb_write(struct fb_info *info, const char __user 
> *buf,
> +                               size_t count, loff_t *ppos)
> +{
> +     struct drm_fb_helper *fb_helper = info->par;
> +     struct drm_client_buffer *buffer = fb_helper->buffer;
> +
> +     if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> +             return drm_fb_helper_sys_write(info, buf, count, ppos);
> +     else
> +             return drm_fb_helper_cfb_write(info, buf, count, ppos);
> +}
> +
> +static void drm_fbdev_fb_fillrect(struct fb_info *info,
> +                               const struct fb_fillrect *rect)
> +{
> +     struct drm_fb_helper *fb_helper = info->par;
> +     struct drm_client_buffer *buffer = fb_helper->buffer;
> +
> +     if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> +             drm_fb_helper_sys_fillrect(info, rect);
> +     else
> +             drm_fb_helper_cfb_fillrect(info, rect);
> +}
> +
> +static void drm_fbdev_fb_copyarea(struct fb_info *info,
> +                               const struct fb_copyarea *area)
> +{
> +     struct drm_fb_helper *fb_helper = info->par;
> +     struct drm_client_buffer *buffer = fb_helper->buffer;
> +
> +     if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> +             drm_fb_helper_sys_copyarea(info, area);
> +     else
> +             drm_fb_helper_cfb_copyarea(info, area);
> +}
> +
> +static void drm_fbdev_fb_imageblit(struct fb_info *info,
> +                                const struct fb_image *image)
> +{
> +     struct drm_fb_helper *fb_helper = info->par;
> +     struct drm_client_buffer *buffer = fb_helper->buffer;
> +
> +     if (drm_fbdev_use_shadow_fb(fb_helper) || !buffer->map.is_iomem)
> +             drm_fb_helper_sys_imageblit(info, image);
> +     else
> +             drm_fb_helper_cfb_imageblit(info, image);
> +}
> +
>  static const struct fb_ops drm_fbdev_fb_ops = {
>       .owner          = THIS_MODULE,
>       DRM_FB_HELPER_DEFAULT_OPS,
> @@ -2034,11 +2223,11 @@ 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