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[ Upstream commit2a1658bf92] Recent kernels have been reported to panic using the bochs_drm framebuffer under qemu-system-sparc64 which was bisected to commit7a0483ac4f("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.