Re: [PATCH v3 6/8] iommu/arm-smmu: Add impl hook for inherit boot mappings

From: Robin Murphy <robin.murphy@arm.com>
To: Bjorn Andersson <bjorn.andersson@linaro.org>,
	Will Deacon <will@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	Jordan Crouse <jcrouse@codeaurora.org>,
	Rob Clark <robdclark@chromium.org>
Cc: linux-arm-msm@vger.kernel.org, iommu@lists.linux-foundation.org,
	Sibi Sankar <sibis@codeaurora.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 6/8] iommu/arm-smmu: Add impl hook for inherit boot mappings
Date: Fri, 11 Sep 2020 18:13:01 +0100	[thread overview]
Message-ID: <0bfcc8f7-d054-616b-834b-319461b1ecb9@arm.com> (raw)
In-Reply-To: <20200904155513.282067-7-bjorn.andersson@linaro.org>

On 2020-09-04 16:55, Bjorn Andersson wrote:
> Add a new operation to allow platform implementations to inherit any
> stream mappings from the boot loader.

Is there a reason we need an explicit step for this? The aim of the 
cfg_probe hook is that the SMMU software state should all be set up by 
then, and you can mess about with it however you like before 
arm_smmu_reset() actually commits anything to hardware. I would have 
thought you could permanently steal a context bank, configure it as your 
bypass hole, read out the previous SME configuration and tweak 
smmu->smrs and smmu->s2crs appropriately all together "invisibly" at 
that point. If that can't work, I'm very curious as to what I've overlooked.

Robin.

> Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> ---
> 
> Changes since v2:
> - New patch/interface
> 
>   drivers/iommu/arm/arm-smmu/arm-smmu.c | 11 ++++++-----
>   drivers/iommu/arm/arm-smmu/arm-smmu.h |  6 ++++++
>   2 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index eb5c6ca5c138..4c4d302cd747 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -85,11 +85,6 @@ static inline void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
>   		pm_runtime_put_autosuspend(smmu->dev);
>   }
>   
> -static struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> -{
> -	return container_of(dom, struct arm_smmu_domain, domain);
> -}
> -
>   static struct platform_driver arm_smmu_driver;
>   static struct iommu_ops arm_smmu_ops;
>   
> @@ -2188,6 +2183,12 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>   	if (err)
>   		return err;
>   
> +	if (smmu->impl->inherit_mappings) {
> +		err = smmu->impl->inherit_mappings(smmu);
> +		if (err)
> +			return err;
> +	}
> +
>   	if (smmu->version == ARM_SMMU_V2) {
>   		if (smmu->num_context_banks > smmu->num_context_irqs) {
>   			dev_err(dev,
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> index 235d9a3a6ab6..f58164976e74 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> @@ -378,6 +378,11 @@ struct arm_smmu_domain {
>   	struct iommu_domain		domain;
>   };
>   
> +static inline struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> +{
> +	return container_of(dom, struct arm_smmu_domain, domain);
> +}
> +
>   struct arm_smmu_master_cfg {
>   	struct arm_smmu_device		*smmu;
>   	s16				smendx[];
> @@ -442,6 +447,7 @@ struct arm_smmu_impl {
>   	int (*alloc_context_bank)(struct arm_smmu_domain *smmu_domain,
>   				  struct arm_smmu_device *smmu,
>   				  struct device *dev, int start);
> +	int (*inherit_mappings)(struct arm_smmu_device *smmu);
>   };
>   
>   #define INVALID_SMENDX			-1
> 
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