linux-kernel - Re: [PATCH] iommu/iova: Fix module config properly

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Message-ID: <4740744e-2e12-520d-8598-188b8d2ebd6b@huawei.com>
Date:   Tue, 13 Sep 2022 14:01:36 +0100
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, <joro@...tes.org>
CC:     <will@...nel.org>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH] iommu/iova: Fix module config properly

On 13/09/2022 12:47, Robin Murphy wrote:
> IOMMU_IOVA is intended to be an optional library for users to select as
> and when they desire. Since it can be a module now, this means that
> built-in code which has chosen not to select it should not fail to link
> if it happens to have selected as a module by someone else. Replace
> IS_ENABLED() with IS_REACHABLE() to do the right thing.

Hi Robin,

Recently you mentioned "I wonder if we couldn't replace the IS_ENABLED() 
with IS_REACHABLE() and restore some of the previously-conditional 
selects", and pointed me to 84db889e6d82 as an example of when a 
conditional select was made unconditional.

So will you also restore some previously-conditional selects next?

To me, it seems that any user of IOVA API selects IOMMU_IOVA always.

thanks,
John

> 
> CC: Thierry Reding <thierry.reding@...il.com>
> Reported-by: John Garry <john.garry@...wei.com>
> Fixes: 15bbdec3931e ("iommu: Make the iova library a module")
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> 
> Phrased as a fix for the sake of complete honesty, but it seems
> everyone's been making do for years already so by now it's really
> just more of an enhancement.
> 
>   include/linux/iova.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index 8f97a43be834..fe18c3e6a725 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -75,7 +75,7 @@ static inline unsigned long iova_pfn(struct iova_domain *iovad, dma_addr_t iova)
>   	return iova >> iova_shift(iovad);
>   }
>   
> -#if IS_ENABLED(CONFIG_IOMMU_IOVA)
> +#if IS_REACHABLE(CONFIG_IOMMU_IOVA)
>   int iova_cache_get(void);
>   void iova_cache_put(void);
>