Re: [PATCH v5 4/8] drm/cma-helper: Use the generic fbdev emulation

[John Stultz <john.stultz@linaro.org>]

On Tue, Jul 3, 2018 at 9:03 AM, Noralf Trønnes <noralf@tronnes.org> wrote:
> This switches the CMA helper drivers that use its fbdev emulation over
> to the generic fbdev emulation. It's the first phase of using generic
> fbdev. A later phase will use DRM client callbacks for the
> lastclose/hotplug/remove callbacks.
>
> There are currently 2 fbdev init/fini functions:
> - drm_fb_cma_fbdev_init/drm_fb_cma_fbdev_fini
> - drm_fbdev_cma_init/drm_fbdev_cma_fini
>
> This is because the work on generic fbdev came up during a fbdev
> refactoring and thus wasn't completed. No point in completing that
> refactoring when drivers will soon move to drm_fb_helper_generic_probe().
>
> tinydrm uses drm_fb_cma_fbdev_init_with_funcs().
>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_fb_cma_helper.c | 360 +++++-------------------------------
>  include/drm/drm_fb_cma_helper.h     |   3 -
>  2 files changed, 42 insertions(+), 321 deletions(-)
...
> -static int drm_fbdev_cma_defio_init(struct fb_info *fbi,
> -                                   struct drm_gem_cma_object *cma_obj)
> -{
> -       struct fb_deferred_io *fbdefio;
> -       struct fb_ops *fbops;
> -
> -       /*
> -        * Per device structures are needed because:
> -        * fbops: fb_deferred_io_cleanup() clears fbops.fb_mmap
> -        * fbdefio: individual delays
> -        */
> -       fbdefio = kzalloc(sizeof(*fbdefio), GFP_KERNEL);
> -       fbops = kzalloc(sizeof(*fbops), GFP_KERNEL);
> -       if (!fbdefio || !fbops) {
> -               kfree(fbdefio);
> -               kfree(fbops);
> -               return -ENOMEM;
> -       }
> -
> -       /* can't be offset from vaddr since dirty() uses cma_obj */
> -       fbi->screen_buffer = cma_obj->vaddr;
> -       /* fb_deferred_io_fault() needs a physical address */
> -       fbi->fix.smem_start = page_to_phys(virt_to_page(fbi->screen_buffer));
> -
> -       *fbops = *fbi->fbops;
> -       fbi->fbops = fbops;
> -
> -       fbdefio->delay = msecs_to_jiffies(DEFAULT_FBDEFIO_DELAY_MS);
> -       fbdefio->deferred_io = drm_fb_helper_deferred_io;
> -       fbi->fbdefio = fbdefio;
> -       fb_deferred_io_init(fbi);
> -       fbi->fbops->fb_mmap = drm_fbdev_cma_deferred_io_mmap;
> -
> -       return 0;
> -}
> -
> -static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
> -{
> -       if (!fbi->fbdefio)
> -               return;
> -
> -       fb_deferred_io_cleanup(fbi);
> -       kfree(fbi->fbdefio);
> -       kfree(fbi->fbops);
> -}
> -
> -static int
> -drm_fbdev_cma_create(struct drm_fb_helper *helper,
> -       struct drm_fb_helper_surface_size *sizes)
> -{
> -       struct drm_fbdev_cma *fbdev_cma = to_fbdev_cma(helper);
> -       struct drm_device *dev = helper->dev;
> -       struct drm_gem_cma_object *obj;
> -       struct drm_framebuffer *fb;
> -       unsigned int bytes_per_pixel;
> -       unsigned long offset;
> -       struct fb_info *fbi;
> -       size_t size;
> -       int ret;
> -
> -       DRM_DEBUG_KMS("surface width(%d), height(%d) and bpp(%d)\n",
> -                       sizes->surface_width, sizes->surface_height,
> -                       sizes->surface_bpp);
> -
> -       bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
> -       size = sizes->surface_width * sizes->surface_height * bytes_per_pixel;
> -       obj = drm_gem_cma_create(dev, size);
> -       if (IS_ERR(obj))
> -               return -ENOMEM;
> -
> -       fbi = drm_fb_helper_alloc_fbi(helper);
> -       if (IS_ERR(fbi)) {
> -               ret = PTR_ERR(fbi);
> -               goto err_gem_free_object;
> -       }
> -
> -       fb = drm_gem_fbdev_fb_create(dev, sizes, 0, &obj->base,
> -                                    fbdev_cma->fb_funcs);
> -       if (IS_ERR(fb)) {
> -               dev_err(dev->dev, "Failed to allocate DRM framebuffer.\n");
> -               ret = PTR_ERR(fb);
> -               goto err_fb_info_destroy;
> -       }
> -
> -       helper->fb = fb;
> -
> -       fbi->par = helper;
> -       fbi->flags = FBINFO_FLAG_DEFAULT;
> -       fbi->fbops = &drm_fbdev_cma_ops;
> -
> -       drm_fb_helper_fill_fix(fbi, fb->pitches[0], fb->format->depth);
> -       drm_fb_helper_fill_var(fbi, helper, sizes->fb_width, sizes->fb_height);
> -
> -       offset = fbi->var.xoffset * bytes_per_pixel;
> -       offset += fbi->var.yoffset * fb->pitches[0];
> -
> -       dev->mode_config.fb_base = (resource_size_t)obj->paddr;
> -       fbi->screen_base = obj->vaddr + offset;
> -       fbi->fix.smem_start = (unsigned long)(obj->paddr + offset);

Hey Noralf, all,
  I've been digging for a bit on the regression that this patch has
tripped on the HiKey board as reported here:
https://lkml.org/lkml/2018/8/16/81

The first issue was that the kirin driver was setting
mode_config.max_width/height = 2048, which was causing errors as the
the requested resolution was 1920x2160 (due to surfaceflinger
requesting y*2 for page flipping).  This was relatively simple enough
to figure out and fix, but bumping the values up on its own didn't
seem to resolve the issue entirely, as I started to see hard hangs on
bootup when userspace started using the emulated fbdev device.

After confirming reverting the patch here worked around it, I started
digging through what might be different, and I think I've found it.
In the drm_fbdev_cma_create() function above, we set the
fbi->fix.smem_start value, where as in drm_fb_helper_generic_probe(),
which now replaces that, we don't set smem_start value at all.

Since we don't have a drm_gem_cma_object reference in
drm_fb_helper_generic_probe(), I instead added:
   fbi->fix.smem_start = page_to_phys(virt_to_page(fbi->screen_buffer));

And that got things working!

So yea, I wanted to figure out if we are just missing the line above
in drm_fb_helper_generic_probe()? Or if the kirin driver should be
setting the fix.smem_start in some other fashion?

thanks
-john
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