Re: [PATCH v5 5/8] iommu/arm-smmu-v3: Add bypass flag to arm_smmu_write_strtab_ent()

[Robin Murphy]

On 2021-05-24 12:02, Shameer Kolothum wrote:
> By default, disable_bypass is set and any dev without an iommu domain
> installs STE with CFG_ABORT during arm_smmu_init_bypass_stes(). Introduce
> a "bypass" flag to arm_smmu_write_strtab_ent() so that we can force it to
> install CFG_BYPASS STE for specific SIDs. This will be useful in follow
> up patch to install bypass for IORT RMR SIDs.
> 
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi at huawei.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 754bad6092c1..f9195b740f48 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -1174,7 +1174,7 @@ static void arm_smmu_sync_ste_for_sid(struct arm_smmu_device *smmu, u32 sid)
>   }
>   
>   static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
> -				      __le64 *dst)
> +				      __le64 *dst, bool bypass)
>   {
>   	/*
>   	 * This is hideously complicated, but we only really care about
> @@ -1245,7 +1245,7 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>   
>   	/* Bypass/fault */
>   	if (!smmu_domain || !(s1_cfg || s2_cfg)) {
> -		if (!smmu_domain && disable_bypass)
> +		if (!smmu_domain && disable_bypass && !bypass)

Umm...

>   			val |= FIELD_PREP(STRTAB_STE_0_CFG, STRTAB_STE_0_CFG_ABORT);
>   		else
>   			val |= FIELD_PREP(STRTAB_STE_0_CFG, STRTAB_STE_0_CFG_BYPASS);
> @@ -1320,7 +1320,7 @@ static void arm_smmu_init_bypass_stes(__le64 *strtab, unsigned int nent)
>   	unsigned int i;
>   
>   	for (i = 0; i < nent; ++i) {
> -		arm_smmu_write_strtab_ent(NULL, -1, strtab);
> +		arm_smmu_write_strtab_ent(NULL, -1, strtab, false);

...and in particular, an operation named "init_bypass_stes" passing 
bypass=false is just breaking my brain. Can we pull the logic for 
default bypass/fault out to here as part of the refactoring so that it 
actually makes sense?

Robin.

>   		strtab += STRTAB_STE_DWORDS;
>   	}
>   }
> @@ -2097,7 +2097,7 @@ static void arm_smmu_install_ste_for_dev(struct arm_smmu_master *master)
>   		if (j < i)
>   			continue;
>   
> -		arm_smmu_write_strtab_ent(master, sid, step);
> +		arm_smmu_write_strtab_ent(master, sid, step, false);
>   	}
>   }
>   
>