linux-kernel - Re: [PATCH] Revert "ARM: dma-mapping: Set proper DMA ops in arm_iommu_detach

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Message-ID: <20190114160902.GB9218@ulmo>
Date:   Mon, 14 Jan 2019 17:09:03 +0100
From:   Thierry Reding <treding@...dia.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
CC:     <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Ben Skeggs <bskeggs@...hat.com>,
        Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH] Revert "ARM: dma-mapping: Set proper DMA ops in
 arm_iommu_detach_device()"

On Mon, Jan 14, 2019 at 02:22:40PM +0100, Marek Szyprowski wrote:
> This reverts commit 1874619a7df4b14b23b14877e705ae15325773e3.
> 
> That patch broke IOMMU support for devices, which fails to probe for the
> first time and use deferred probe approach. When non-NULL dma_ops is set
> in arm_iommu_detach_device(), the given device later ignored by
> arch_setup_dma_ops() and stays with non-IOMMU dma_ops.
> 
> Reported-by: Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
> Fixes: 1874619a7df4 "ARM: dma-mapping: Set proper DMA ops in arm_iommu_detach_device()"
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  arch/arm/mm/dma-mapping.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)

Can you point out exactly what drivers break because of this change? We
need to find a solution that works for everyone. Reverting is only
marginally useful because somebody will just end up wanting to revert
the revert because a different driver is now broken.

Thierry

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