From 2a1658bf922ffd9b7907e270a7d9cdc9643fc45d Mon Sep 17 00:00:00 2001 From: Sam Ravnborg Date: Thu, 9 Jul 2020 21:30:16 +0200 Subject: drm/drm_fb_helper: fix fbdev with sparc64 Recent kernels have been reported to panic using the bochs_drm framebuffer under qemu-system-sparc64 which was bisected to commit 7a0483ac4ffc ("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 Reported-by: Mark Cave-Ayland Reported-by: kernel test robot Tested-by: Mark Cave-Ayland Reviewed-by: Daniel Vetter Cc: Mark Cave-Ayland Cc: Thomas Zimmermann Cc: Gerd Hoffmann Cc: "David S. Miller" 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 --- drivers/gpu/drm/bochs/bochs_kms.c | 1 + 1 file changed, 1 insertion(+) (limited to 'drivers/gpu/drm/bochs') diff --git a/drivers/gpu/drm/bochs/bochs_kms.c b/drivers/gpu/drm/bochs/bochs_kms.c index 05d8373888e8..079f46f5cdb6 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.fbdev_use_iomem = true; bochs->dev->mode_config.quirk_addfb_prefer_host_byte_order = true; bochs->dev->mode_config.funcs = &bochs_mode_funcs; -- cgit v1.2.3