releases/4.8.17/drivers-gpu-drm-ast-fix-infinite-loop-if-read-fails.patch

From 298360af3dab45659810fdc51aba0c9f4097e4f6 Mon Sep 17 00:00:00 2001
From: Russell Currey <ruscur@russell.cc>
Date: Thu, 15 Dec 2016 16:12:41 +1100
Subject: drivers/gpu/drm/ast: Fix infinite loop if read fails

From: Russell Currey <ruscur@russell.cc>

commit 298360af3dab45659810fdc51aba0c9f4097e4f6 upstream.

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.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/ast/ast_main.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- 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_
 	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 *d
 	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);
 	}