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Date:   Fri, 19 Mar 2021 01:01:11 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     linux-kernel@vger.kernel.org, opendmb@gmail.com,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        "open list:SWIOTLB SUBSYSTEM" <iommu@lists.linux-foundation.org>
Subject: Re: [PATCH] swiotlb: Make SWIOTLB_NO_FORCE perform no allocation
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References: <20210318191816.4185226-1-f.fainelli@gmail.com>
 <20210319040055.183433-1-f.fainelli@gmail.com>
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On Thu, Mar 18, 2021 at 09:00:54PM -0700, Florian Fainelli wrote:
> When SWIOTLB_NO_FORCE is used, there should really be no allocations of
> io_tlb_nslabs to occur since we are not going to use those slabs. If a
> platform was somehow setting swiotlb_no_force and a later call to
> swiotlb_init() was to be made we would still be proceeding with
> allocating the default SWIOTLB size (64MB), whereas if swiotlb=noforce
> was set on the kernel command line we would have only allocated 2KB.
> 
> This would be inconsistent and the point of initializing io_tlb_nslabs
> to 1, was to avoid hitting the test for io_tlb_nslabs being 0/not
> initialized.

Could you rebase this on devel/for-linus-5.13 in

git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb.git

please?
> 
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
>  kernel/dma/swiotlb.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index c10e855a03bc..526c8321b76f 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -121,12 +121,10 @@ setup_io_tlb_npages(char *str)
>  	}
>  	if (*str == ',')
>  		++str;
> -	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;
> -		io_tlb_nslabs = 1;
> -	}
>  
>  	return 0;
>  }
> @@ -284,6 +282,9 @@ swiotlb_init(int verbose)
>  	unsigned char *vstart;
>  	unsigned long bytes;
>  
> +	if (swiotlb_force == SWIOTLB_NO_FORCE)
> +		goto out;
> +
>  	if (!io_tlb_nslabs) {
>  		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
>  		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
> @@ -302,6 +303,7 @@ swiotlb_init(int verbose)
>  		io_tlb_start = 0;
>  	}
>  	pr_warn("Cannot allocate buffer");
> +out:
>  	no_iotlb_memory = true;
>  }
>  
> -- 
> 2.25.1
>