Commit 4bba72b7 authored Jul 09, 2020 by Sam Ravnborg Committed by Greg Kroah-Hartman Aug 11, 2020

drm/drm_fb_helper: fix fbdev with sparc64



[ Upstream commit 2a1658bf922ffd9b7907e270a7d9cdc9643fc45d ]

Recent kernels have been reported to panic using the bochs_drm
framebuffer under qemu-system-sparc64 which was bisected to
commit 7a0483ac ("drm/bochs: switch to generic drm fbdev emulation").

The backtrace indicates that the shadow framebuffer copy in
drm_fb_helper_dirty_blit_real() is trying to access the real
framebuffer using a virtual address rather than use an IO access
typically implemented using a physical (ASI_PHYS) access on SPARC.

The fix is to replace the memcpy with memcpy_toio() from io.h.

memcpy_toio() uses writeb() where the original fbdev code
used sbus_memcpy_toio(). The latter uses sbus_writeb().

The difference between writeb() and sbus_memcpy_toio() is
that writeb() writes bytes in little-endian, where sbus_writeb() writes
bytes in big-endian. As endian does not matter for byte writes they are
the same. So we can safely use memcpy_toio() here.

Note that this only fixes bochs, in general fbdev helpers still have
issues with mixing up system memory and __iomem space. Fixing that will
require a lot more work.

v3:
  - Improved changelog (Daniel)
  - Added FIXME to fbdev_use_iomem (Daniel)

v2:
  - Added missing __iomem cast (kernel test robot)
  - Made changelog readable and fix typos (Mark)
  - Add flag to select iomem - and set it in the bochs driver

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reported-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200709193016.291267-1-sam@ravnborg.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200725191012.GA434957@ravnborg.org


Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 8e6af828

drivers/gpu/drm/bochs/bochs_kms.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -194,6 +194,7 @@ 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.fbdev_use_iomem = true;
		bochs->dev->mode_config.quirk_addfb_prefer_host_byte_order = true;

		bochs->dev->mode_config.funcs = &bochs_mode_funcs;

drivers/gpu/drm/drm_fb_helper.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -390,7 +390,11 @@ static void drm_fb_helper_dirty_blit_real(struct drm_fb_helper *fb_helper,
		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);

		src += fb->pitches[0];
		dst += fb->pitches[0];
		}

include/drm/drm_mode_config.h

+12 −0

Original line number	Diff line number	Diff line
		@@ -865,6 +865,18 @@ 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:
		*