linux-kernel - Re: [PATCH 15/15] dma-mapping: bypass indirect calls for dma-direct

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Message-ID: <20181220164608.GA20000@lst.de>
Date:   Thu, 20 Dec 2018 17:46:08 +0100
From:   Christoph Hellwig <hch@....de>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Keith Busch <keith.busch@...el.com>,
        Jonathan Derrick <jonathan.derrick@...el.com>,
        linux-pci@...r.kernel.org, linux-ia64@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/15] dma-mapping: bypass indirect calls for dma-direct

On Thu, Dec 20, 2018 at 05:44:18PM +0100, Thierry Reding wrote:
> On Fri, Dec 07, 2018 at 11:07:20AM -0800, Christoph Hellwig wrote:
> [...]
> > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> > index 0b18cfbdde95..fc84c81029d9 100644
> > --- a/kernel/dma/mapping.c
> > +++ b/kernel/dma/mapping.c
> [...]
> > @@ -397,9 +404,9 @@ int dma_supported(struct device *dev, u64 mask)
> >  {
> >  	const struct dma_map_ops *ops = get_dma_ops(dev);
> >  
> > -	if (!ops)
> > -		return 0;
> > -	if (!ops->dma_supported)
> > +	if (dma_is_direct(ops))
> > +		return dma_direct_supported(dev, mask);
> > +	if (ops->dma_supported)
> >  		return 1;
> >  	return ops->dma_supported(dev, mask);
> >  }
> 
> Hi Christoph,
> 
> This hunk causes a crash on boot for me. It looks like a ! got lost in
> the rework here. The following patch fixes the crash for me and restores
> the logic of the op->dma_supported check.
> 
> Feel free to squash this patch into the above if you prefer that.

I don't want to rebase, so I'll pick this up ASAP.