linux-kernel - Re: [PATCH v3 6/6] iommu: mtk_iommu: Lookup phandle to retrieve syscon to pericfg

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Message-ID: <8b31b1d2-4ed7-11a1-2124-4641c8f3abcd@gmail.com>
Date:   Wed, 15 Jun 2022 14:09:49 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, yong.wu@...iatek.com
Cc:     joro@...tes.org, will@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        iommu@...ts.linux-foundation.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        krzysztof.kozlowski@...aro.org
Subject: Re: [PATCH v3 6/6] iommu: mtk_iommu: Lookup phandle to retrieve
 syscon to pericfg



On 09/06/2022 12:08, AngeloGioacchino Del Regno wrote:
> On some SoCs (of which only MT8195 is supported at the time of writing),
> the "R" and "W" (I/O) enable bits for the IOMMUs are in the pericfg_ao
> register space and not in the IOMMU space: as it happened already with
> infracfg, it is expected that this list will grow.
> 
> Instead of specifying pericfg compatibles on a per-SoC basis, following
> what was done with infracfg, let's lookup the syscon by phandle instead.
> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>   drivers/iommu/mtk_iommu.c | 23 +++++++++++++----------
>   1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 90685946fcbe..0ea0848581e9 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -138,6 +138,8 @@
>   /* PM and clock always on. e.g. infra iommu */
>   #define PM_CLK_AO			BIT(15)
>   #define IFA_IOMMU_PCIE_SUPPORT		BIT(16)
> +/* IOMMU I/O (r/w) is enabled using PERICFG_IOMMU_1 register */
> +#define HAS_PERI_IOMMU1_REG		BIT(17)

 From what I can see MTK_IOMMU_TYPE_INFRA is only set in MT8195 which uses 
pericfg. So we don't need a new flag here. For me the flag name 
MTK_IOMMU_TYPE_INFRA was confusing as it has nothing to do with the use of 
infracfg. I'll hijack this patch to provide some feedback on the actual code, 
please see below.

>   
>   #define MTK_IOMMU_HAS_FLAG_MASK(pdata, _x, mask)	\
>   				((((pdata)->flags) & (mask)) == (_x))
> @@ -187,7 +189,6 @@ struct mtk_iommu_plat_data {
>   	u32			flags;
>   	u32			inv_sel_reg;
>   
> -	char			*pericfg_comp_str;
>   	struct list_head	*hw_list;
>   	unsigned int		iova_region_nr;
>   	const struct mtk_iommu_iova_region	*iova_region;
> @@ -1218,14 +1219,16 @@ static int mtk_iommu_probe(struct platform_device *pdev)
>   			goto out_runtime_disable;
>   		}
>   	} else if (MTK_IOMMU_IS_TYPE(data->plat_data, MTK_IOMMU_TYPE_INFRA) &&
> -		   data->plat_data->pericfg_comp_str) {

Check for pericfg_comp_str is not needed, we only have one platform that uses 
MTK_IOMMU_TYPE_INFRA.

> -		infracfg = syscon_regmap_lookup_by_compatible(data->plat_data->pericfg_comp_str);

We can do something like this to make the code clearer:
data->pericfg = 
syscon_regmap_lookup_by_compatible(data->plat_data->pericfg_comp_str);
		if (IS_ERR(data->pericfg)) {

Using infracfg variable here is confusing as it has nothing to do with infracfg 
used with HAS_4GB_MODE flag.

Regards,
Matthias

> -		if (IS_ERR(infracfg)) {
> -			ret = PTR_ERR(infracfg);
> -			goto out_runtime_disable;
> +		   MTK_IOMMU_HAS_FLAG(data->plat_data, HAS_PERI_IOMMU1_REG)) {
> +		data->pericfg = syscon_regmap_lookup_by_phandle(dev->of_node, "mediatek,pericfg");
> +		if (IS_ERR(data->pericfg)) {
> +			p = "mediatek,mt8195-pericfg_ao";
> +			data->pericfg = syscon_regmap_lookup_by_compatible(p);
> +			if (IS_ERR(data->pericfg)) {
> +				ret = PTR_ERR(data->pericfg);
> +				goto out_runtime_disable;
> +			}
>   		}
> -
> -		data->pericfg = infracfg;
>   	}
>   
>   	platform_set_drvdata(pdev, data);
> @@ -1484,8 +1487,8 @@ static const struct mtk_iommu_plat_data mt8192_data = {
>   static const struct mtk_iommu_plat_data mt8195_data_infra = {
>   	.m4u_plat	  = M4U_MT8195,
>   	.flags            = WR_THROT_EN | DCM_DISABLE | STD_AXI_MODE | PM_CLK_AO |
> -			    MTK_IOMMU_TYPE_INFRA | IFA_IOMMU_PCIE_SUPPORT,
> -	.pericfg_comp_str = "mediatek,mt8195-pericfg_ao",
> +			    HAS_PERI_IOMMU1_REG | MTK_IOMMU_TYPE_INFRA |
> +			    IFA_IOMMU_PCIE_SUPPORT,
>   	.inv_sel_reg      = REG_MMU_INV_SEL_GEN2,
>   	.banks_num	  = 5,
>   	.banks_enable     = {true, false, false, false, true},