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

[Russell Currey]

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 at vger.kernel.org> # 3.10+
Signed-off-by: Russell Currey <ruscur at russell.cc>
---
 drivers/gpu/drm/ast/ast_main.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index 904beaa..f75c642 100644
--- 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);
 
@@ -428,7 +429,9 @@ 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);
 	}
-- 
2.10.2