[PATCH 4/4] iommu/mediatek: check 4GB mode by reading infracfg

[Miles Chen <miles.chen@mediatek.com>]

In previous disscusion [1] and [2], we found that it is risky to
use max_pfn or totalram_pages to tell if 4GB mode is enabled.

Check 4GB mode by reading infracfg register, remove the usage
of the unexported symbol max_pfn.

[1] https://lkml.org/lkml/2020/6/3/733
[2] https://lkml.org/lkml/2020/6/4/136

Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Yong Wu <yong.wu@mediatek.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
---
 drivers/iommu/mtk_iommu.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
index 2be96f1cdbd2..09be57bd8d74 100644
--- a/drivers/iommu/mtk_iommu.c
+++ b/drivers/iommu/mtk_iommu.c
@@ -3,7 +3,6 @@
  * Copyright (c) 2015-2016 MediaTek Inc.
  * Author: Yong Wu <yong.wu@mediatek.com>
  */
-#include <linux/memblock.h>
 #include <linux/bug.h>
 #include <linux/clk.h>
 #include <linux/component.h>
@@ -15,11 +14,13 @@
 #include <linux/iommu.h>
 #include <linux/iopoll.h>
 #include <linux/list.h>
+#include <linux/mfd/syscon.h>
 #include <linux/of_address.h>
 #include <linux/of_iommu.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/regmap.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <asm/barrier.h>
@@ -91,6 +92,9 @@
 #define F_MMU_INT_ID_LARB_ID(a)			(((a) >> 7) & 0x7)
 #define F_MMU_INT_ID_PORT_ID(a)			(((a) >> 2) & 0x1f)
 
+#define REG_INFRA_MISC				0xf00
+#define F_DDR_4GB_SUPPORT_EN			BIT(13)
+
 #define MTK_PROTECT_PA_ALIGN			128
 
 /*
@@ -599,8 +603,10 @@ static int mtk_iommu_probe(struct platform_device *pdev)
 	struct resource         *res;
 	resource_size_t		ioaddr;
 	struct component_match  *match = NULL;
+	struct regmap		*infracfg_regmap;
 	void                    *protect;
 	int                     i, larb_nr, ret;
+	u32			val;
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
@@ -614,10 +620,18 @@ static int mtk_iommu_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	data->protect_base = ALIGN(virt_to_phys(protect), MTK_PROTECT_PA_ALIGN);
 
-	/* Whether the current dram is over 4GB */
-	data->enable_4GB = !!(max_pfn > (BIT_ULL(32) >> PAGE_SHIFT));
-	if (!data->plat_data->has_4gb_mode)
+	if (data->plat_data->has_4gb_mode) {
+		infracfg_regmap = syscon_regmap_lookup_by_phandle(dev->of_node,
+				"mediatek,infracfg");
+		if (IS_ERR(infracfg_regmap))
+			return PTR_ERR(infracfg_regmap);
+		ret = regmap_read(infracfg_regmap, REG_INFRA_MISC, &val);
+		if (ret)
+			return ret;
+		data->enable_4GB = !!(val & F_DDR_4GB_SUPPORT_EN);
+	} else {
 		data->enable_4GB = false;
+	}
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	data->base = devm_ioremap_resource(dev, res);
-- 
2.18.0