Re: [PATCH v3 2/3] memory: mtk-smi: Add enable IOMMU SMC command for MM master

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 27/07/22 12:45, Chengci.Xu ha scritto:
> For concerns about security, the register to enable/disable IOMMU of
> SMI LARB should only be configured in secure world. Thus, we add some
> SMC command for multimedia master to enable/disable MM IOMMU in ATF by
> setting the register of SMI LARB. This function is prepared for MT8188.
> 
> Signed-off-by: Chengci.Xu <chengci.xu@mediatek.com>
> ---
>   drivers/memory/mtk-smi.c                 | 11 +++++++++++
>   include/linux/soc/mediatek/mtk_sip_svc.h |  3 +++
>   include/soc/mediatek/smi.h               |  7 +++++++
>   3 files changed, 21 insertions(+)
> 
> diff --git a/drivers/memory/mtk-smi.c b/drivers/memory/mtk-smi.c
> index d7cb7ead2ac7..41ce66c39123 100644
> --- a/drivers/memory/mtk-smi.c
> +++ b/drivers/memory/mtk-smi.c
> @@ -3,6 +3,7 @@
>    * Copyright (c) 2015-2016 MediaTek Inc.
>    * Author: Yong Wu <yong.wu@mediatek.com>
>    */
> +#include <linux/arm-smccc.h>
>   #include <linux/clk.h>
>   #include <linux/component.h>
>   #include <linux/device.h>
> @@ -14,6 +15,7 @@
>   #include <linux/of_platform.h>
>   #include <linux/platform_device.h>
>   #include <linux/pm_runtime.h>
> +#include <linux/soc/mediatek/mtk_sip_svc.h>
>   #include <soc/mediatek/smi.h>
>   #include <dt-bindings/memory/mt2701-larb-port.h>
>   #include <dt-bindings/memory/mtk-memory-port.h>
> @@ -89,6 +91,7 @@
>   #define MTK_SMI_FLAG_THRT_UPDATE	BIT(0)
>   #define MTK_SMI_FLAG_SW_FLAG		BIT(1)
>   #define MTK_SMI_FLAG_SLEEP_CTL		BIT(2)
> +#define MTK_SMI_FLAG_SEC_REG		BIT(3)
>   #define MTK_SMI_CAPS(flags, _x)		(!!((flags) & (_x)))
>   
>   struct mtk_smi_reg_pair {
> @@ -235,6 +238,7 @@ static void mtk_smi_larb_config_port_gen2_general(struct device *dev)
>   	struct mtk_smi_larb *larb = dev_get_drvdata(dev);
>   	u32 reg, flags_general = larb->larb_gen->flags_general;
>   	const u8 *larbostd = larb->larb_gen->ostd ? larb->larb_gen->ostd[larb->larbid] : NULL;
> +	struct arm_smccc_res res;
>   	int i;
>   
>   	if (BIT(larb->larbid) & larb->larb_gen->larb_direct_to_common_mask)
> @@ -259,6 +263,13 @@ static void mtk_smi_larb_config_port_gen2_general(struct device *dev)
>   		reg |= BANK_SEL(larb->bank[i]);
>   		writel(reg, larb->base + SMI_LARB_NONSEC_CON(i));
>   	}
> +
> +	if (MTK_SMI_CAPS(flags_general, MTK_SMI_FLAG_SEC_REG)) {
> +		arm_smccc_smc(MTK_SIP_KERNEL_IOMMU_CONTROL, IOMMU_ATF_CMD_CONFIG_SMI_LARB,
> +			      larb->larbid, (u32)(*larb->mmu), 0, 0, 0, 0, &res);
> +		if (res.a0 != 0)
> +			dev_err(dev, "Enable iommu fail, ret %ld\n", res.a0);

This means that the system will eventually crash or anyway be unstable: in this
case, we should not allow further interaction with the IOMMUs and/or SMI.

So, if you place this here, you will have to change this function to return
something for the caller to take action.

> +	}
>   }
>   
>   static const u8 mtk_smi_larb_mt8195_ostd[][SMI_LARB_PORT_NR_MAX] = {
> diff --git a/include/linux/soc/mediatek/mtk_sip_svc.h b/include/linux/soc/mediatek/mtk_sip_svc.h
> index 082398e0cfb1..0761128b4354 100644
> --- a/include/linux/soc/mediatek/mtk_sip_svc.h
> +++ b/include/linux/soc/mediatek/mtk_sip_svc.h
> @@ -22,4 +22,7 @@
>   	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, MTK_SIP_SMC_CONVENTION, \
>   			   ARM_SMCCC_OWNER_SIP, fn_id)
>   
> +/* IOMMU related SMC call */
> +#define MTK_SIP_KERNEL_IOMMU_CONTROL	MTK_SIP_SMC_CMD(0x514)
> +
>   #endif
> diff --git a/include/soc/mediatek/smi.h b/include/soc/mediatek/smi.h
> index 11f7d6b59642..8c781b7bd88d 100644
> --- a/include/soc/mediatek/smi.h
> +++ b/include/soc/mediatek/smi.h
> @@ -9,6 +9,13 @@
>   #include <linux/bitops.h>
>   #include <linux/device.h>
>   
> +/* IOMMU & SMI ATF CMD */
> +
> +enum IOMMU_ATF_CMD {

Why do you have an enumeration when you're defining just one command?
Is it expected to have more?

Besides, the enum name should be lower case, and...

> +	IOMMU_ATF_CMD_CONFIG_SMI_LARB,		/* For mm master to en/disable iommu */
> +	IOMMU_ATF_CMD_COUNT,

if IOMMU_ATF_CMD_COUNT means "end of this enumeration", please call it
IOMMU_ATF_CMD_MAX instead.

> +};
> +
>   #if IS_ENABLED(CONFIG_MTK_SMI)
>   
>   #define MTK_SMI_MMU_EN(port)	BIT(port)