linux-kernel - Re: [PATCH 07/21] dma-iommu: move the arm64 wrappers to common code

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Message-ID: <20190409171511.GC14679@lst.de>
Date:   Tue, 9 Apr 2019 19:15:11 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/21] dma-iommu: move the arm64 wrappers to common code

On Tue, Apr 09, 2019 at 04:07:02PM +0100, Robin Murphy wrote:
>> +static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
>> +		size_t size, enum dma_data_direction dir, unsigned long attrs)
>> +{
>> +	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
>> +		iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir);
>> +	__iommu_dma_unmap(iommu_get_domain_for_dev(dev), dma_handle, size);
>
> That wants to be iommu_get_dma_domain() there to minimise the overhead. In 
> fact, I guess this could now be streamlined a bit in the style of 
> iommu_dma_map_page() above - i.e. avoid doing a second domain lookup in the 
> sync case - but that can happen later (if indeed you haven't already).

Yes, this should be iommu_get_dma_domain - this got lost during
a rebase to the kernel version that changed to the iommu_get_dma_domain
calls.

I don't think I've optimized to remove the additional call, but
I can easily throw in another patch to do that.