linux-kernel - Re: [PATCH v13 06/10] iommu/arm-smmu-v3: Add acpi_smmu_acpi_probe

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Message-ID: <3256d9ce-2c10-4cdd-b4c4-358f2c30a9a3@arm.com>
Date: Tue, 27 Aug 2024 16:57:48 +0100
From: Robin Murphy <robin.murphy@....com>
To: Will Deacon <will@...nel.org>, Nicolin Chen <nicolinc@...dia.com>
Cc: joro@...tes.org, jgg@...dia.com, thierry.reding@...il.com,
 vdumpa@...dia.com, jonathanh@...dia.com, linux-kernel@...r.kernel.org,
 iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-tegra@...r.kernel.org
Subject: Re: [PATCH v13 06/10] iommu/arm-smmu-v3: Add
 acpi_smmu_acpi_probe_model for impl

On 27/08/2024 2:02 pm, Will Deacon wrote:
> On Fri, Aug 23, 2024 at 05:10:40PM -0700, Nicolin Chen wrote:
>> For model-specific implementation, repurpose the acpi_smmu_get_options()
>> to a wider acpi_smmu_acpi_probe_model(). A new model can add to the list
>> in this new function.
>>
>> Suggested-by: Will Deacon <will@...nel.org>
>> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
>> ---
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 18 +++++++++++++-----
>>   1 file changed, 13 insertions(+), 5 deletions(-)
>>
>> 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 afdb8a76a72a..ceb31d63f79b 100644
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> @@ -4341,18 +4341,28 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
>>   }
>>   
>>   #ifdef CONFIG_ACPI
>> -static void acpi_smmu_get_options(u32 model, struct arm_smmu_device *smmu)
>> +static int acpi_smmu_iort_probe_model(struct acpi_iort_node *node,
>> +				      struct arm_smmu_device *smmu)
>>   {
>> -	switch (model) {
>> +	struct acpi_iort_smmu_v3 *iort_smmu =
>> +		(struct acpi_iort_smmu_v3 *)node->node_data;
>> +
>> +	switch (iort_smmu->model) {
>>   	case ACPI_IORT_SMMU_V3_CAVIUM_CN99XX:
>>   		smmu->options |= ARM_SMMU_OPT_PAGE0_REGS_ONLY;
>>   		break;
>>   	case ACPI_IORT_SMMU_V3_HISILICON_HI161X:
>>   		smmu->options |= ARM_SMMU_OPT_SKIP_PREFETCH;
>>   		break;
>> +	case ACPI_IORT_SMMU_V3_GENERIC:
>> +		break;
>> +	default:
>> +		dev_err(smmu->dev, "Unknown/unsupported IORT model!\n");
>> +		return -ENXIO;
> 
> We probably don't want this 'default' case, otherwise the driver will
> need to be updated every time there's a new model.

...although the intent is very strongly that there should never be any 
new models, because by now hardware should really not be failing to 
implement SMMU_IIDR correctly. In some ways, having this might help 
further discourage people from abusing the mechanism and making random 
stuff up in their firmware :/

Cheers,
Robin.