linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: fixed check process for disable

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Date:   Wed, 3 Aug 2022 10:25:37 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Shuuichirou Ishii <ishii.shuuichir@...itsu.com>, will@...nel.org,
        joro@...tes.org, thunder.leizhen@...wei.com, jgg@...pe.ca,
        tglx@...utronix.de, chenxiang66@...ilicon.com,
        christophe.jaillet@...adoo.fr, john.garry@...wei.com,
        baolu.lu@...ux.intel.com, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/arm-smmu-v3: fixed check process for disable_bypass
 module parameter

On 2022-08-03 00:42, Shuuichirou Ishii wrote:
> The current process does not enable the bypass setting regardless of
> the value of the disable_bypass module parameter when ACPI is enabled,
> so the value of the disable_bypass module parameter has been corrected
> so that it is handled correctly.
> 
> Signed-off-by: Shuuichirou Ishii <ishii.shuuichir@...itsu.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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 88817a3376ef..256d7b2a83a7 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3396,7 +3396,7 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass)
>   		enables &= ~(CR0_EVTQEN | CR0_PRIQEN);
>   
>   	/* Enable the SMMU interface, or ensure bypass */
> -	if (!bypass || disable_bypass) {
> +	if (!bypass && disable_bypass) {

This change looks obviously wrong - if bypass is false here then we 
definitely want to enable the SMMU, so disable_bypass is irrelevant. It 
shouldn't even be possible to get here with bypass==true under ACPI, 
since arm_smmu_device_acpi_probe() cannot fail :/

Robin.

>   		enables |= CR0_SMMUEN;
>   	} else {
>   		ret = arm_smmu_update_gbpa(smmu, 0, GBPA_ABORT);