Re: [PATCH 2/2] iommu/arm-smmu: Allow client devices to select direct mapping

[Robin Murphy]

On 2020-01-22 11:48 am, Sai Prakash Ranjan wrote:
> From: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
>
> Some client devices want to directly map the IOMMU themselves instead
> of using the DMA domain. Allow those devices to opt in to direct
> mapping by way of a list of compatible strings.
>
> Signed-off-by: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
> Co-developed-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> ---
>   drivers/iommu/arm-smmu-qcom.c | 39 +++++++++++++++++++++++++++++++++++
>   drivers/iommu/arm-smmu.c      |  3 +++
>   drivers/iommu/arm-smmu.h      |  5 +++++
>   3 files changed, 47 insertions(+)
>
> diff --git a/drivers/iommu/arm-smmu-qcom.c b/drivers/iommu/arm-smmu-qcom.c
> index 64a4ab270ab7..ff746acd1c81 100644
> --- a/drivers/iommu/arm-smmu-qcom.c
> +++ b/drivers/iommu/arm-smmu-qcom.c
> @@ -3,6 +3,7 @@
>    * Copyright (c) 2019, The Linux Foundation. All rights reserved.
>    */
>   
> +#include <linux/of_device.h>
>   #include <linux/qcom_scm.h>
>   
>   #include "arm-smmu.h"
> @@ -11,6 +12,43 @@ struct qcom_smmu {
>   	struct arm_smmu_device smmu;
>   };
>   
> +static const struct arm_smmu_client_match_data qcom_adreno = {
> +	.direct_mapping = true,
> +};
> +
> +static const struct arm_smmu_client_match_data qcom_mdss = {
> +	.direct_mapping = true,
> +};

Might it make sense to group these by the desired SMMU behaviour rather 
than (apparently) what kind of device the client happens to be, which 
seems like a completely arbitrary distinction from the SMMU driver's PoV?

> +
> +static const struct of_device_id qcom_smmu_client_of_match[] = {
> +	{ .compatible = "qcom,adreno", .data = &qcom_adreno },
> +	{ .compatible = "qcom,mdp4", .data = &qcom_mdss },
> +	{ .compatible = "qcom,mdss", .data = &qcom_mdss },
> +	{ .compatible = "qcom,sc7180-mdss", .data = &qcom_mdss },
> +	{ .compatible = "qcom,sdm845-mdss", .data = &qcom_mdss },
> +	{},
> +};
> +
> +static const struct arm_smmu_client_match_data *
> +qcom_smmu_client_data(struct device *dev)
> +{
> +	const struct of_device_id *match =
> +		of_match_device(qcom_smmu_client_of_match, dev);
> +
> +	return match ? match->data : NULL;

of_device_get_match_data() is your friend.

> +}
> +
> +static int qcom_smmu_request_domain(struct device *dev)
> +{
> +	const struct arm_smmu_client_match_data *client;
> +
> +	client = qcom_smmu_client_data(dev);
> +	if (client)
> +		iommu_request_dm_for_dev(dev);
> +
> +	return 0;
> +}
> +
>   static int qcom_sdm845_smmu500_reset(struct arm_smmu_device *smmu)
>   {
>   	int ret;
> @@ -41,6 +79,7 @@ static int qcom_smmu500_reset(struct arm_smmu_device *smmu)
>   }
>   
>   static const struct arm_smmu_impl qcom_smmu_impl = {
> +	.req_domain = qcom_smmu_request_domain,
>   	.reset = qcom_smmu500_reset,
>   };
>   
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 16c4b87af42b..67dd9326247a 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1448,6 +1448,9 @@ static int arm_smmu_add_device(struct device *dev)
>   	device_link_add(dev, smmu->dev,
>   			DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_SUPPLIER);
>   
> +	if (smmu->impl && smmu->impl->req_domain)
> +		return smmu->impl->req_domain(dev);
> +

There are about 5 different patchsets flying around at the moment that 
all touch default domain allocation, so this is a fast-moving target, 
but I think where the dust should settle is with arm_smmu_ops forwarding 
.def_domain_type (or whatever it ends up as) calls to arm_smmu_impl as 
appropriate.

>   	return 0;
>   
>   out_cfg_free:
> diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> index 8d1cd54d82a6..059dc9c39f64 100644
> --- a/drivers/iommu/arm-smmu.h
> +++ b/drivers/iommu/arm-smmu.h
> @@ -244,6 +244,10 @@ enum arm_smmu_arch_version {
>   	ARM_SMMU_V2,
>   };
>   
> +struct arm_smmu_client_match_data {
> +	bool direct_mapping;
> +};

Does this need to be public? I don't see the other users...

Robin.

> +
>   enum arm_smmu_implementation {
>   	GENERIC_SMMU,
>   	ARM_MMU500,
> @@ -386,6 +390,7 @@ struct arm_smmu_impl {
>   	int (*init_context)(struct arm_smmu_domain *smmu_domain);
>   	void (*tlb_sync)(struct arm_smmu_device *smmu, int page, int sync,
>   			 int status);
> +	int (*req_domain)(struct device *dev);
>   };
>   
>   static inline void __iomem *arm_smmu_page(struct arm_smmu_device *smmu, int n)