Re: [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver

Will Deacon
2015-03-06T10:58:27Z

On Fri, Mar 06, 2015 at 10:48:17AM +0000, yong.wu@mediatek.com wrote:
> From: Yong Wu <yong.wu@mediatek.com>
>
> This patch adds support for mediatek m4u (MultiMedia Memory Management Unit).
> Currently this only supports m4u gen 2 with 2 levels of page table on mt8173.

[...]

> diff --git a/drivers/iommu/mtk_iommu_pagetable.c b/drivers/iommu/mtk_iommu_pagetable.c
> new file mode 100644
> index 0000000..5fe9640
> --- /dev/null
> +++ b/drivers/iommu/mtk_iommu_pagetable.c
> @@ -0,0 +1,439 @@
> +/*
> + * Copyright (c) 2014-2015 MediaTek Inc.
> + * Author: Yong Wu <yong.wu@mediatek.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +#include <linux/err.h>
> +#include <linux/mm.h>
> +#include <linux/iommu.h>
> +#include <linux/errno.h>
> +#include "asm/cacheflush.h"
> +
> +#include "mtk_iommu.h"
> +#include "mtk_iommu_pagetable.h"
> +
> +/* 2 level pagetable: pgd -> pte */
> +#define F_PTE_TYPE_GET(regval) (regval & 0x3)
> +#define F_PTE_TYPE_LARGE BIT(0)
> +#define F_PTE_TYPE_SMALL BIT(1)
> +#define F_PTE_B_BIT BIT(2)
> +#define F_PTE_C_BIT BIT(3)
> +#define F_PTE_BIT32_BIT BIT(9)
> +#define F_PTE_S_BIT BIT(10)
> +#define F_PTE_NG_BIT BIT(11)
> +#define F_PTE_PA_LARGE_MSK (~0UL << 16)
> +#define F_PTE_PA_LARGE_GET(regval) ((regval >> 16) & 0xffff)
> +#define F_PTE_PA_SMALL_MSK (~0UL << 12)
> +#define F_PTE_PA_SMALL_GET(regval) ((regval >> 12) & (~0))
> +#define F_PTE_TYPE_IS_LARGE_PAGE(pte) ((imu_pte_val(pte) & 0x3) == \
> + F_PTE_TYPE_LARGE)
> +#define F_PTE_TYPE_IS_SMALL_PAGE(pte) ((imu_pte_val(pte) & 0x3) == \
> + F_PTE_TYPE_SMALL)

This looks like the ARM short-descriptor format to me. Could you please
add a new page table format to the io-pgtable code, so that other IOMMU
drivers can make use of this? I know there was some interest in using
short descriptor for the ARM SMMU, for example.

Cheers,

Will