From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Russell Currey <ruscur@russell.cc>
Date: Thu, 15 Dec 2016 16:12:41 +1100
Subject: [PATCH 12/13] drivers/gpu/drm/ast: Fix infinite loop if read fails

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: Joel Stanley <joel@jms.id.au>
---
 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 e0b4586a26fd..9b8f0b975ca6 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);
 
@@ -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);
 	}
-- 
2.11.0