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Subject: Re: [PATCH 4/4] iommu/mediatek: check 4GB mode by reading infracfg
To:     Miles Chen <miles.chen@mediatek.com>,
        Joerg Roedel <joro@8bytes.org>,
        Rob Herring <robh+dt@kernel.org>
Cc:     iommu@lists.linux-foundation.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
        Yong Wu <yong.wu@mediatek.com>,
        Chao Hao <chao.hao@mediatek.com>,
        Yingjoe Chen <yingjoe.chen@mediatek.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Christoph Hellwig <hch@lst.de>
References: <20200702093721.6063-1-miles.chen@mediatek.com>
 <20200702093721.6063-4-miles.chen@mediatek.com>
From:   Matthias Brugger <matthias.bgg@gmail.com>
Message-ID: <84333997-735c-4a91-6d47-1dcb5c4a6078@gmail.com>
Date:   Wed, 15 Jul 2020 23:05:09 +0200
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On 02/07/2020 11:37, Miles Chen wrote:
> 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)
> +

As this is used for infracfg, I think it would be good to add it to 
include/linux/soc/mediatek/infracfg.h and include that file here.

>   #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;

Maybe call it just infracfg.

>   	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);

Do we need to error out, or could we be conservative and set endable_4GB = false?

> +		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;

Move that before the if() and update enable_4GB only in case of has_4gb_mode.

> +	}
>   
>   	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>   	data->base = devm_ioremap_resource(dev, res);
>