iommu/mediatek: Check 4GB mode by reading infracfg

In previous discussion [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 un-exported symbol max_pfn.

This is a step towards building mtk_iommu as a kernel module.

[1] https://lore.kernel.org/lkml/20200603161132.2441-1-miles.chen@mediatek.com/
[2] https://lore.kernel.org/lkml/20200604080120.2628-1-miles.chen@mediatek.com/
[3] https://lore.kernel.org/lkml/20200715205120.GA778876@bogus/

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>
Cc: Rob Herring <robh@kernel.org>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Joerg Roedel <joro@8bytes.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Link: https://lore.kernel.org/r/20200904104038.4979-1-miles.chen@mediatek.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

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>
@@ -15,13 +14,16 @@
 #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 <linux/soc/mediatek/infracfg.h>
 #include <asm/barrier.h>
 #include <soc/mediatek/smi.h>
 
@@ -640,8 +642,11 @@ static int mtk_iommu_probe(struct platform_device *pdev)
 	struct resource         *res;
 	resource_size_t		ioaddr;
 	struct component_match  *match = NULL;
+	struct regmap		*infracfg;
 	void                    *protect;
 	int                     i, larb_nr, ret;
+	u32			val;
+	char                    *p;
 
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
@@ -655,10 +660,28 @@ 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 (!MTK_IOMMU_HAS_FLAG(data->plat_data, HAS_4GB_MODE))
-		data->enable_4GB = false;
+	if (MTK_IOMMU_HAS_FLAG(data->plat_data, HAS_4GB_MODE)) {
+		switch (data->plat_data->m4u_plat) {
+		case M4U_MT2712:
+			p = "mediatek,mt2712-infracfg";
+			break;
+		case M4U_MT8173:
+			p = "mediatek,mt8173-infracfg";
+			break;
+		default:
+			p = NULL;
+		}
+
+		infracfg = syscon_regmap_lookup_by_compatible(p);
+
+		if (IS_ERR(infracfg))
+			return PTR_ERR(infracfg);
+
+		ret = regmap_read(infracfg, REG_INFRA_MISC, &val);
+		if (ret)
+			return ret;
+		data->enable_4GB = !!(val & F_DDR_4GB_SUPPORT_EN);
+	}
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	data->base = devm_ioremap_resource(dev, res);

include/linux/soc/mediatek/infracfg.h

@@ -32,6 +32,9 @@
 #define MT7622_TOP_AXI_PROT_EN_WB		(BIT(2) | BIT(6) | \
 						 BIT(7) | BIT(8))
 
+#define REG_INFRA_MISC				0xf00
+#define F_DDR_4GB_SUPPORT_EN			BIT(13)
+
 int mtk_infracfg_set_bus_protection(struct regmap *infracfg, u32 mask,
 		bool reg_update);
 int mtk_infracfg_clear_bus_protection(struct regmap *infracfg, u32 mask,