linux-kernel - Re: [PATCH v2] swiotlb: Make SWIOTLB_NO

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Date:   Mon, 22 Mar 2021 08:46:27 +0100
From:   Christoph Hellwig <hch@....de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "open list:SWIOTLB SUBSYSTEM" <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH v2] swiotlb: Make SWIOTLB_NO_FORCE perform no allocation

On Sat, Mar 20, 2021 at 08:37:40PM -0700, Florian Fainelli wrote:
> -	if (!strcmp(str, "force")) {
> +	if (!strcmp(str, "force"))
>  		swiotlb_force = SWIOTLB_FORCE;
> -	} else if (!strcmp(str, "noforce")) {
> +	else if (!strcmp(str, "noforce"))
>  		swiotlb_force = SWIOTLB_NO_FORCE;
> -		default_nslabs = 1;
> -	}
>  
>  	return 0;
>  }
> @@ -211,6 +209,9 @@ swiotlb_init(int verbose)
>  	size_t bytes = PAGE_ALIGN(default_nslabs << IO_TLB_SHIFT);
>  	void *tlb;
>  
> +	if (swiotlb_force == SWIOTLB_NO_FORCE)
> +		return;

We'll also need this in the other callers of swiotlb_init_with_tbl
and swiotlb_late_init_with_tbl.

I actually had a plan to mostly kill them, but that can better
way until more support for multiple io_tlb structures is merged.