linux-kernel - Re: [PATCH 3/4] iommu/exynos: Use lookup based approach to access v7 registers

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Date:   Sun, 3 Jul 2022 21:29:24 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Janghyuck Kim <janghyuck.kim@...sung.com>,
        Cho KyongHo <pullip.cho@...sung.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        iommu@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] iommu/exynos: Use lookup based approach to access v7
 registers

On 02/07/2022 23:37, Sam Protsenko wrote:
> SysMMU v7 might have different register layouts (VM capable or non-VM
> capable). Check which layout is implemented in current SysMMU module and
> prepare the corresponding register table for futher usage. This way is
> faster and more elegant than checking corresponding condition (if it's
> VM or non-VM SysMMU) each time before accessing v7 registers. For now
> the register table contains only most basic registers needed to add the
> SysMMU v7 support.
> 
> This patch is based on downstream work of next authors:
>   - Janghyuck Kim <janghyuck.kim@...sung.com>
>   - Daniel Mentz <danielmentz@...gle.com>
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> ---
>  drivers/iommu/exynos-iommu.c | 46 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/drivers/iommu/exynos-iommu.c b/drivers/iommu/exynos-iommu.c
> index df6ddbebbe2b..47017e8945c5 100644
> --- a/drivers/iommu/exynos-iommu.c
> +++ b/drivers/iommu/exynos-iommu.c
> @@ -180,6 +180,47 @@ static u32 lv2ent_offset(sysmmu_iova_t iova)
>  
>  #define has_sysmmu(dev)		(dev_iommu_priv_get(dev) != NULL)
>  
> +#define MMU_REG(data, idx)		\
> +	((data)->sfrbase + (data)->regs[idx].off)

I would expect to see users of this - convert all existing regs.

> +#define MMU_VM_REG(data, idx, vmid)	\
> +	(MMU_REG(data, idx) + (vmid) * (data)->regs[idx].mult)
> +
> +enum {
> +	REG_SET_NON_VM,
> +	REG_SET_VM,
> +	MAX_REG_SET
> +};
> +
> +enum {
> +	IDX_CTRL_VM,
> +	IDX_CFG_VM,
> +	IDX_FLPT_BASE,

Isn't this called REG_MMU_FLUSH? If yes, it's a bit confusing to see
different name used.

> +	IDX_ALL_INV,

Isn't this called REG_MMU_FLUSH_ENTRY?

> +	MAX_REG_IDX
> +};
> +
> +struct sysmmu_vm_reg {
> +	unsigned int off;	/* register offset */
> +	unsigned int mult;	/* VM index offset multiplier */
> +};
> +
> +static const struct sysmmu_vm_reg sysmmu_regs[MAX_REG_SET][MAX_REG_IDX] = {
> +	/* Default register set (non-VM) */
> +	{
> +		/*
> +		 * SysMMUs without VM support do not have CTRL_VM and CFG_VM
> +		 * registers. Setting the offsets to 1 will trigger an unaligned
> +		 * access exception.

So why are you setting offset 1? To trigger unaligned access?

> +		 */
> +		{0x1}, {0x1}, {0x000c}, {0x0010},
> +	},
> +	/* VM capable register set */
> +	{
> +		{0x8000, 0x1000}, {0x8004, 0x1000}, {0x800c, 0x1000},
> +		{0x8010, 0x1000},
> +	},
You add here quite a bit of dead code and some hard-coded numbers.

> +};
> +
>  static struct device *dma_dev;
>  static struct kmem_cache *lv2table_kmem_cache;
>  static sysmmu_pte_t *zero_lv2_table;
> @@ -284,6 +325,7 @@ struct sysmmu_drvdata {
>  
>  	/* v7 fields */
>  	bool has_vcr;			/* virtual machine control register */
> +	const struct sysmmu_vm_reg *regs; /* register set */
>  };
>  
>  static struct exynos_iommu_domain *to_exynos_domain(struct iommu_domain *dom)
> @@ -407,6 +449,10 @@ static void sysmmu_get_hw_info(struct sysmmu_drvdata *data)
>  	__sysmmu_get_version(data);
>  	if (MMU_MAJ_VER(data->version) >= 7 && __sysmmu_has_capa1(data))
>  		__sysmmu_get_vcr(data);
> +	if (data->has_vcr)
> +		data->regs = sysmmu_regs[REG_SET_VM];
> +	else
> +		data->regs = sysmmu_regs[REG_SET_NON_VM];

This is set and not read.

>  
>  	__sysmmu_disable_clocks(data);
>  }


Best regards,
Krzysztof