linux-kernel - Re: [PATCH] ARM: Qualify enabling of swiotlb

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Date:   Fri, 19 Mar 2021 14:07:31 +0100
From:   Christoph Hellwig <hch@....de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.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>,
        open list <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Catalin Marinas <catalin.marinas@....com>, opendmb@...il.com
Subject: Re: [PATCH] ARM: Qualify enabling of swiotlb_init()

On Thu, Mar 18, 2021 at 09:03:33PM -0700, Florian Fainelli wrote:
>  #ifdef CONFIG_ARM_LPAE
> +	if (swiotlb_force == SWIOTLB_FORCE ||
> +	    max_pfn > arm_dma_pfn_limit)

Does arm_dma_pfn_limit do the right thing even with the weirdest
remapping ranges?  Maybe a commen here would be useful.

> +		swiotlb_init(1);
> +	else
> +		swiotlb_force = SWIOTLB_NO_FORCE;

Konrad: what do you think of setting swiotlb_force to SWIOTLB_NO_FORCE
and only switching it to SWIOTLB_NORMAL when swiotlb_init* is called?
That kind makes more sense than forcing the callers to do it.

While we're at it, I think swiotlb_force should probably be renamed to
swiotlb_mode or somethng like that.