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

From: Sai Prakash Ranjan <[email-masked]>
Date: Thu, 16 Apr 2020 21:53:58 +0530

Hi Robin,

On 2020-04-16 19:28, Robin Murphy wrote:
> On 2020-01-22 11:48 am, Sai Prakash Ranjan wrote:
>> From: Jordan Crouse <[email-masked]>
>> 
>> 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 <[email-masked]>
>> Co-developed-by: Sai Prakash Ranjan <[email-masked]>
>> Signed-off-by: Sai Prakash Ranjan <[email-masked]>
>> ---
>>   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?
> 

Sorry, I did not get the "grouping by the desired SMMU behaviour" thing.
Could you please give some more details?

>> +
>> +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.
> 

Ok will use it.

>> +}
>> +
>> +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.
> 

I'll wait till the dust settles down and then post the next version.

>>   	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...
> 

Will move this out.

Thanks,
Sai

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