drm/ast: Handle configuration without P2A bridge

The ast driver configures a window to enable access into BMC
memory space in order to read some configuration registers.

If this window is disabled, which it can be from the BMC side,
the ast driver can't function.

Closing this window is a necessity for security if a machine's
host side and BMC side are controlled by different parties;
i.e. a cloud provider offering machines "bare metal".

A recent patch went in to try to check if that window is open
but it does so by trying to access the registers in question
and testing if the result is 0xffffffff.

This method will trigger a PCIe error when the window is closed
which on some systems will be fatal (it will trigger an EEH
for example on POWER which will take out the device).

This patch improves this in two ways:

 - First, if the firmware has put properties in the device-tree
containing the relevant configuration information, we use these.

 - Otherwise, a bit in one of the SCU scratch registers (which
are readable via the VGA register space and writeable by the BMC)
will indicate if the BMC has closed the window. This bit has been
defined by Y.C Chen from Aspeed.

If the window is closed and the configuration isn't available from
the device-tree, some sane defaults are used. Those defaults are
hopefully sufficient for standard video modes used on a server.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Acked-by: Joel Stanley <joel@jms.id.au>
Cc: <stable@vger.kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ast/ast_drv.h

@@ -114,7 +114,11 @@ struct ast_private {
 	struct ttm_bo_kmap_obj cache_kmap;
 	int next_cursor;
 	bool support_wide_screen;
-	bool DisableP2A;
+	enum {
+		ast_use_p2a,
+		ast_use_dt,
+		ast_use_defaults
+	} config_mode;
 
 	enum ast_tx_chip tx_chip_type;
 	u8 dp501_maxclk;

drivers/gpu/drm/ast/ast_main.c

@@ -62,13 +62,84 @@ uint8_t ast_get_index_reg_mask(struct ast_private *ast,
 	return ret;
 }
 
+static void ast_detect_config_mode(struct drm_device *dev, u32 *scu_rev)
+{
+	struct device_node *np = dev->pdev->dev.of_node;
+	struct ast_private *ast = dev->dev_private;
+	uint32_t data, jregd0, jregd1;
+
+	/* Defaults */
+	ast->config_mode = ast_use_defaults;
+	*scu_rev = 0xffffffff;
+
+	/* Check if we have device-tree properties */
+	if (np && !of_property_read_u32(np, "aspeed,scu-revision-id",
+					scu_rev)) {
+		/* We do, disable P2A access */
+		ast->config_mode = ast_use_dt;
+		DRM_INFO("Using device-tree for configuration\n");
+		return;
+	}
+
+	/* Not all families have a P2A bridge */
+	if (dev->pdev->device != PCI_CHIP_AST2000)
+		return;
+
+	/*
+	 * The BMC will set SCU 0x40 D[12] to 1 if the P2 bridge
+	 * is disabled. We force using P2A if VGA only mode bit
+	 * is set D[7]
+	 */
+	jregd0 = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xd0, 0xff);
+	jregd1 = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xd1, 0xff);
+	if (!(jregd0 & 0x80) || !(jregd1 & 0x10)) {
+		/* Double check it's actually working */
+		data = ast_read32(ast, 0xf004);
+		if (data != 0xFFFFFFFF) {
+			/* P2A works, grab silicon revision */
+			ast->config_mode = ast_use_p2a;
+
+			DRM_INFO("Using P2A bridge for configuration\n");
+
+			/* Read SCU7c (silicon revision register) */
+			ast_write32(ast, 0xf004, 0x1e6e0000);
+			ast_write32(ast, 0xf000, 0x1);
+			*scu_rev = ast_read32(ast, 0x1207c);
+			return;
+		}
+	}
+
+	/* We have a P2A bridge but it's disabled */
+	DRM_INFO("P2A bridge disabled, using default configuration\n");
+}
 
 static int ast_detect_chip(struct drm_device *dev, bool *need_post)
 {
 	struct ast_private *ast = dev->dev_private;
-	uint32_t data, jreg;
+	uint32_t jreg, scu_rev;
+
+	/*
+	 * If VGA isn't enabled, we need to enable now or subsequent
+	 * access to the scratch registers will fail. We also inform
+	 * our caller that it needs to POST the chip
+	 * (Assumption: VGA not enabled -> need to POST)
+	 */
+	if (!ast_is_vga_enabled(dev)) {
+		ast_enable_vga(dev);
+		DRM_INFO("VGA not enabled on entry, requesting chip POST\n");
+		*need_post = true;
+	} else
+		*need_post = false;
+
+
+	/* Enable extended register access */
+	ast_enable_mmio(dev);
 	ast_open_key(ast);
 
+	/* Find out whether P2A works or whether to use device-tree */
+	ast_detect_config_mode(dev, &scu_rev);
+
+	/* Identify chipset */
 	if (dev->pdev->device == PCI_CHIP_AST1180) {
 		ast->chip = AST1100;
 		DRM_INFO("AST 1180 detected\n");
@@ -80,12 +151,7 @@ static int ast_detect_chip(struct drm_device *dev, bool *need_post)
 			ast->chip = AST2300;
 			DRM_INFO("AST 2300 detected\n");
 		} else if (dev->pdev->revision >= 0x10) {
-			uint32_t data;
-			ast_write32(ast, 0xf004, 0x1e6e0000);
-			ast_write32(ast, 0xf000, 0x1);
-
-			data = ast_read32(ast, 0x1207c);
-			switch (data & 0x0300) {
+			switch (scu_rev & 0x0300) {
 			case 0x0200:
 				ast->chip = AST1100;
 				DRM_INFO("AST 1100 detected\n");
@@ -110,26 +176,6 @@ static int ast_detect_chip(struct drm_device *dev, bool *need_post)
 		}
 	}
 
-	/*
-	 * If VGA isn't enabled, we need to enable now or subsequent
-	 * access to the scratch registers will fail. We also inform
-	 * our caller that it needs to POST the chip
-	 * (Assumption: VGA not enabled -> need to POST)
-	 */
-	if (!ast_is_vga_enabled(dev)) {
-		ast_enable_vga(dev);
-		ast_enable_mmio(dev);
-		DRM_INFO("VGA not enabled on entry, requesting chip POST\n");
-		*need_post = true;
-	} else
-		*need_post = false;
-
-	/* Check P2A Access */
-	ast->DisableP2A = true;
-	data = ast_read32(ast, 0xf004);
-	if (data != 0xFFFFFFFF)
-		ast->DisableP2A = false;
-
 	/* Check if we support wide screen */
 	switch (ast->chip) {
 	case AST1180:
@@ -146,17 +192,12 @@ static int ast_detect_chip(struct drm_device *dev, bool *need_post)
 			ast->support_wide_screen = true;
 		else {
 			ast->support_wide_screen = false;
-			if (ast->DisableP2A == false) {
-				/* Read SCU7c (silicon revision register) */
-				ast_write32(ast, 0xf004, 0x1e6e0000);
-				ast_write32(ast, 0xf000, 0x1);
-				data = ast_read32(ast, 0x1207c);
-				data &= 0x300;
-				if (ast->chip == AST2300 && data == 0x0) /* ast1300 */
-					ast->support_wide_screen = true;
-				if (ast->chip == AST2400 && data == 0x100) /* ast1400 */
-					ast->support_wide_screen = true;
-			}
+			if (ast->chip == AST2300 &&
+			    (scu_rev & 0x300) == 0x0) /* ast1300 */
+				ast->support_wide_screen = true;
+			if (ast->chip == AST2400 &&
+			    (scu_rev & 0x300) == 0x100) /* ast1400 */
+				ast->support_wide_screen = true;
 		}
 		break;
 	}
@@ -220,85 +261,102 @@ static int ast_detect_chip(struct drm_device *dev, bool *need_post)
 
 static int ast_get_dram_info(struct drm_device *dev)
 {
+	struct device_node *np = dev->pdev->dev.of_node;
 	struct ast_private *ast = dev->dev_private;
-	uint32_t data, data2;
-	uint32_t denum, num, div, ref_pll;
+	uint32_t mcr_cfg, mcr_scu_mpll, mcr_scu_strap;
+	uint32_t denum, num, div, ref_pll, dsel;
 
-	if (ast->DisableP2A)
-	{
+	switch (ast->config_mode) {
+	case ast_use_dt:
+		/*
+		 * If some properties are missing, use reasonable
+		 * defaults for AST2400
+		 */
+		if (of_property_read_u32(np, "aspeed,mcr-configuration",
+					 &mcr_cfg))
+			mcr_cfg = 0x00000577;
+		if (of_property_read_u32(np, "aspeed,mcr-scu-mpll",
+					 &mcr_scu_mpll))
+			mcr_scu_mpll = 0x000050C0;
+		if (of_property_read_u32(np, "aspeed,mcr-scu-strap",
+					 &mcr_scu_strap))
+			mcr_scu_strap = 0;
+		break;
+	case ast_use_p2a:
+		ast_write32(ast, 0xf004, 0x1e6e0000);
+		ast_write32(ast, 0xf000, 0x1);
+		mcr_cfg = ast_read32(ast, 0x10004);
+		mcr_scu_mpll = ast_read32(ast, 0x10120);
+		mcr_scu_strap = ast_read32(ast, 0x10170);
+		break;
+	case ast_use_defaults:
+	default:
 		ast->dram_bus_width = 16;
 		ast->dram_type = AST_DRAM_1Gx16;
 		ast->mclk = 396;
+		return 0;
 	}
-	else
-	{
-		ast_write32(ast, 0xf004, 0x1e6e0000);
-		ast_write32(ast, 0xf000, 0x1);
-		data = ast_read32(ast, 0x10004);
-
-		if (data & 0x40)
-			ast->dram_bus_width = 16;
-		else
-			ast->dram_bus_width = 32;
 
-		if (ast->chip == AST2300 || ast->chip == AST2400) {
-			switch (data & 0x03) {
-			case 0:
-				ast->dram_type = AST_DRAM_512Mx16;
-				break;
-			default:
-			case 1:
-				ast->dram_type = AST_DRAM_1Gx16;
-				break;
-			case 2:
-				ast->dram_type = AST_DRAM_2Gx16;
-				break;
-			case 3:
-				ast->dram_type = AST_DRAM_4Gx16;
-				break;
-			}
-		} else {
-			switch (data & 0x0c) {
-			case 0:
-			case 4:
-				ast->dram_type = AST_DRAM_512Mx16;
-				break;
-			case 8:
-				if (data & 0x40)
-					ast->dram_type = AST_DRAM_1Gx16;
-				else
-					ast->dram_type = AST_DRAM_512Mx32;
-				break;
-			case 0xc:
-				ast->dram_type = AST_DRAM_1Gx32;
-				break;
-			}
-		}
+	if (mcr_cfg & 0x40)
+		ast->dram_bus_width = 16;
+	else
+		ast->dram_bus_width = 32;
 
-		data = ast_read32(ast, 0x10120);
-		data2 = ast_read32(ast, 0x10170);
-		if (data2 & 0x2000)
-			ref_pll = 14318;
-		else
-			ref_pll = 12000;
-
-		denum = data & 0x1f;
-		num = (data & 0x3fe0) >> 5;
-		data = (data & 0xc000) >> 14;
-		switch (data) {
-		case 3:
-			div = 0x4;
+	if (ast->chip == AST2300 || ast->chip == AST2400) {
+		switch (mcr_cfg & 0x03) {
+		case 0:
+			ast->dram_type = AST_DRAM_512Mx16;
 			break;
-		case 2:
+		default:
 		case 1:
-			div = 0x2;
+			ast->dram_type = AST_DRAM_1Gx16;
 			break;
-		default:
-			div = 0x1;
+		case 2:
+			ast->dram_type = AST_DRAM_2Gx16;
+			break;
+		case 3:
+			ast->dram_type = AST_DRAM_4Gx16;
+			break;
+		}
+	} else {
+		switch (mcr_cfg & 0x0c) {
+		case 0:
+		case 4:
+			ast->dram_type = AST_DRAM_512Mx16;
+			break;
+		case 8:
+			if (mcr_cfg & 0x40)
+				ast->dram_type = AST_DRAM_1Gx16;
+			else
+				ast->dram_type = AST_DRAM_512Mx32;
+			break;
+		case 0xc:
+			ast->dram_type = AST_DRAM_1Gx32;
 			break;
 		}
-		ast->mclk = ref_pll * (num + 2) / (denum + 2) * (div * 1000);
 	}
+
+	if (mcr_scu_strap & 0x2000)
+		ref_pll = 14318;
+	else
+		ref_pll = 12000;
+
+	denum = mcr_scu_mpll & 0x1f;
+	num = (mcr_scu_mpll & 0x3fe0) >> 5;
+	dsel = (mcr_scu_mpll & 0xc000) >> 14;
+	switch (dsel) {
+	case 3:
+		div = 0x4;
+		break;
+	case 2:
+	case 1:
+		div = 0x2;
+		break;
+	default:
+		div = 0x1;
+		break;
+	}
+	ast->mclk = ref_pll * (num + 2) / (denum + 2) * (div * 1000);
 	return 0;
 }
 

drivers/gpu/drm/ast/ast_post.c

@@ -379,17 +379,14 @@ void ast_post_gpu(struct drm_device *dev)
 	ast_open_key(ast);
 	ast_set_def_ext_reg(dev);
 
-	if (ast->DisableP2A == false)
-	{
+	if (ast->config_mode == ast_use_p2a) {
 		if (ast->chip == AST2300 || ast->chip == AST2400)
 			ast_init_dram_2300(dev);
 		else
 			ast_init_dram_reg(dev);
 
 		ast_init_3rdtx(dev);
-	}
-	else
-	{
+	} else {
 		if (ast->tx_chip_type != AST_TX_NONE)
 			ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xa3, 0xcf, 0x80);	/* Enable DVO */
 	}