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

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Date:   Mon, 29 Apr 2019 11:55:54 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>
Cc:     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

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;


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.

Robin.

> +
> +	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
>