linux-kernel - Re: [PATCH v3 01/10] iommu: Add helper to get minimal page size of domain

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Message-ID: <48ac694e-4551-40e2-f914-6942da810489@linux.intel.com>
Date:   Tue, 30 Apr 2019 08:40:20 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, pengfei.xu@...el.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/10] iommu: Add helper to get minimal page size of
 domain

Hi Robin,

On 4/29/19 6:55 PM, Robin Murphy wrote:
> On 21/04/2019 02:17, Lu Baolu wrote:
>> This makes it possible for other modules to know the minimal
>> page size supported by a domain without the knowledge of the
>> structure details.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   include/linux/iommu.h | 13 +++++++++++++
>>   1 file changed, 13 insertions(+)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index a5007d035218..46679ef19b7e 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -377,6 +377,14 @@ static inline void iommu_tlb_sync(struct 
>> iommu_domain *domain)
>>           domain->ops->iotlb_sync(domain);
>>   }
>> +static inline unsigned long domain_minimal_pgsize(struct iommu_domain 
>> *domain)
>> +{
>> +    if (domain && domain->pgsize_bitmap)
>> +        return 1 << __ffs(domain->pgsize_bitmap);
> 
> Nit: this would probably be more efficient on most architectures as:
> 
>      if (domain)
>          return domain->pgsize_bitmap & -domain->pgsize_bitmap;
> 

It looks reasonable to me.

> 
> I'd also suggest s/minimal/min/ in the name, just to stop it getting too 
> long. Otherwise, though, I like the idea, and there's at least one other 
> place (in iommu-dma) that can make use of it straight away.

Okay, I will change the name to domain_min_pgsize().

> 
> Robin.
> 

Best regards,
Lu Baolu

>> +
>> +    return 0;
>> +}
>> +
>>   /* PCI device grouping function */
>>   extern struct iommu_group *pci_device_group(struct device *dev);
>>   /* Generic device grouping function */
>> @@ -704,6 +712,11 @@ const struct iommu_ops 
>> *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
>>       return NULL;
>>   }
>> +static inline unsigned long domain_minimal_pgsize(struct iommu_domain 
>> *domain)
>> +{
>> +    return 0;
>> +}
>> +
>>   #endif /* CONFIG_IOMMU_API */
>>   #ifdef CONFIG_IOMMU_DEBUGFS
>>
>