drivers/gpu/drm/ast: Fix infinite loop if read fails

[ Upstream commit 298360af3dab45659810fdc51aba0c9f4097e4f6 ]

ast_get_dram_info() configures a window in order to access BMC memory.
A BMC register can be configured to disallow this, and if so, causes
an infinite loop in the ast driver which renders the system unusable.

Fix this by erroring out if an error is detected.  On powerpc systems with
EEH, this leads to the device being fenced and the system continuing to
operate.

Cc: <stable@vger.kernel.org> # 3.10+
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161215051241.20815-1-ruscur@russell.cc
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index fd5c5f3370f6b3577c0f8c191485291e1ca62415..e53dbc90fcb602a5e081d50b16bcca054362a67f 100644 (file)
--- a/drivers/gpu/drm/ast/ast_main.c
+++ b/drivers/gpu/drm/ast/ast_main.c
@@ -223,7 +223,8 @@ static int ast_get_dram_info(struct drm_device *dev)
        ast_write32(ast, 0x10000, 0xfc600309);
 
        do {
-               ;
+               if (pci_channel_offline(dev->pdev))
+                       return -EIO;
        } while (ast_read32(ast, 0x10000) != 0x01);
        data = ast_read32(ast, 0x10004);
 
@@ -429,7 +430,9 @@ int ast_driver_load(struct drm_device *dev, unsigned long flags)
        ast_detect_chip(dev, &need_post);
 
        if (ast->chip != AST1180) {
-               ast_get_dram_info(dev);
+               ret = ast_get_dram_info(dev);
+               if (ret)
+                       goto out_free;
                ast->vram_size = ast_get_vram_info(dev);
                DRM_INFO("dram %d %d %d %08x\n", ast->mclk, ast->dram_type, ast->dram_bus_width, ast->vram_size);
        }