Re: [PATCH v4 4/5] iommu/arm-smmu-qcom: Make set_stall work when the device is on

[Will Deacon <will@kernel.org>]

On Tue, Mar 04, 2025 at 11:56:50AM -0500, Connor Abbott wrote:
> Up until now we have only called the set_stall callback during
> initialization when the device is off. But we will soon start calling it
> to temporarily disable stall-on-fault when the device is on, so handle
> that by checking if the device is on and writing SCTLR.
> 
> Signed-off-by: Connor Abbott <cwabbott0@gmail.com>
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> index a428e53add08d451fb2152e3ab80e0fba936e214..d34a0d917013bb3d5a24b3ce72f48e3b38474da2 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
> @@ -77,12 +77,36 @@ static void qcom_adreno_smmu_set_stall(const void *cookie, bool enabled)
>  {
>  	struct arm_smmu_domain *smmu_domain = (void *)cookie;
>  	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
> -	struct qcom_smmu *qsmmu = to_qcom_smmu(smmu_domain->smmu);
> +	struct arm_smmu_device *smmu = smmu_domain->smmu;
> +	struct qcom_smmu *qsmmu = to_qcom_smmu(smmu);
> +	u32 mask = BIT(cfg->cbndx);
> +	bool stall_changed = !!(qsmmu->stall_enabled & mask) != enabled;
> +	unsigned long flags;
>  
>  	if (enabled)
> -		qsmmu->stall_enabled |= BIT(cfg->cbndx);
> +		qsmmu->stall_enabled |= mask;
>  	else
> -		qsmmu->stall_enabled &= ~BIT(cfg->cbndx);
> +		qsmmu->stall_enabled &= ~mask;
> +
> +	/*
> +	 * If the device is on and we changed the setting, update the register.
> +	 */
> +	if (stall_changed && pm_runtime_get_if_active(smmu->dev) > 0) {
> +		spin_lock_irqsave(&smmu_domain->cb_lock, flags);
> +
> +		u32 reg = arm_smmu_cb_read(smmu, cfg->cbndx, ARM_SMMU_CB_SCTLR);
> +
> +		if (enabled)
> +			reg |= ARM_SMMU_SCTLR_CFCFG;
> +		else
> +			reg &= ~ARM_SMMU_SCTLR_CFCFG;
> +
> +		arm_smmu_cb_write(smmu, cfg->cbndx, ARM_SMMU_CB_SCTLR, reg);

Are you sure you don't need TLB invalidation for this to take effect? I
think some fields in the SCTLR can be cached in the TLB but you'll need
to check whether or not that applies to CFCFG.

Will