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: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161215051241.20815-1-ruscur@russell.cc

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index 904beaa932d03f0b5ce7d89a13d16729582052e0..f75c6421db6239c9435ed39dc7d6244d13894920 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);
 
@@ -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);
        }