Panic booting qemu-system-sparc64 with bochs_drm

[Mark Cave-Ayland]

On 04/07/2020 14:41, Sam Ravnborg wrote:

> I think what is happening is that the bochs driver request a shadow copy
> for the frambuffer. And with the change to fbops we now use the cfb_
> functions to write to the shadow framebuffer - which is not in any IO
> space. So this does not work.
> 
> So maybe all we need is the fix in drm_fb_helper_dirty_blit_real().
> If you try to undo the change so fbops is set to &drm_fbdev_fb_ops,
> but keep the fix in drm_fb_helper_dirty_blit_real() how does it then
> behave?

Bingo! I just tried that and the framebuffer is now working under qemu-system-sparc64
again - thank you so much for the help! From what you said I guess
drm_fb_helper_dirty_blit_real() is responsible syncing the shadow copy?

Below is the current working diff based upon your previous one: it certainly feels
like the difference in memcpy() behaviour should be hidden away in fb_memcpy_tofb()
or similar.


diff --git a/drivers/gpu/drm/bochs/bochs_kms.c b/drivers/gpu/drm/bochs/bochs_kms.c
index 05d8373888e8..8dcc09f1ba1d 100644
--- a/drivers/gpu/drm/bochs/bochs_kms.c
+++ b/drivers/gpu/drm/bochs/bochs_kms.c
@@ -146,6 +146,7 @@ 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.use_cfb_for_fbdev = 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 5609e164805f..18d89388b125 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -398,8 +398,13 @@ static void drm_fb_helper_dirty_blit_real(struct drm_fb_helper
*fb_helper,
        size_t len = (clip->x2 - clip->x1) * cpp;
        unsigned int y;

+       // TODO
        for (y = clip->y1; y < clip->y2; y++) {
-               memcpy(dst, src, len);
+               if (fb_helper->dev->mode_config.use_cfb_for_fbdev)
+                       fb_memcpy_tofb(dst, src, len);
+               else
+                       memcpy(dst, src, len);
+
                src += fb->pitches[0];
                dst += fb->pitches[0];
        }
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 6c3ef49b46b3..dce9adf7d189 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -865,6 +865,15 @@ struct drm_mode_config {
         */
        bool prefer_shadow_fbdev;

+       /**
+        * @use_cfb_for_fbdev:
+        *
+        * Use cfb variants of drm_fb_helper_cfb_{fillrect,copyarea,imageblit}
+        * The cfb variants are required when the CPU do not allow direct
+        * access to the framebuffer (for example sparc64)
+        */
+       bool use_cfb_for_fbdev;
+
        /**
         * @quirk_addfb_prefer_xbgr_30bpp:
         *

> I did not find time to follow your instructions to test this myself with
> qemu - sorry.

No worries, I do appreciate that as a maintainer it can be hard to fit these things
around life, family, job etc.


ATB,

Mark.