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

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Message-ID: <20210319195929.GA1346384@konrad-char-us-oracle-com.allregionaliads.osdevelopmeniad.oraclevcn.com>
Date:   Fri, 19 Mar 2021 19:59:36 +0000
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Christoph Hellwig <hch@....de>, xen-devel@...ts.xensource.com,
        sstabellini@...nel.org
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        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 Fri, Mar 19, 2021 at 02:07:31PM +0100, Christoph Hellwig wrote:
> 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.

swiotlb_mode sounds good.

Also it got me thinking - ARM on Xen at some point was a bit strange, so not sure how
the logic works here, Stefano?