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

[Yong Wu <yong.wu@mediatek.com>]

Dear Will,

On Fri, 2015-03-06 at 10:58 +0000, Will Deacon wrote:
> 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.
    Currently I not familiar with the io-pgtable,I may need some time
for it and the ARM short-descriptor. 
    And there are some difference between mediatek's pagetable with the
standard short-descriptor, like bit 9. we use it for the dram over 4GB.
Then how should we do if there are some difference. 
> 
> Cheers,
> 
> Will