linux-kernel - RE: [PATCH v2 7/9] dpaa_eth: fix iova handling for contiguous frames

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Message-ID: <VI1PR04MB513490961A52D86E46C02B49EC340@VI1PR04MB5134.eurprd04.prod.outlook.com>
Date:   Thu, 2 May 2019 09:10:38 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Madalin-cristian Bucur <madalin.bucur@....com>,
        Roy Pledge <roy.pledge@....com>,
        Camelia Alexandra Groza <camelia.groza@....com>,
        Leo Li <leoyang.li@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v2 7/9] dpaa_eth: fix iova handling for contiguous frames



> -----Original Message-----
> From: Christoph Hellwig <hch@...radead.org>
> Sent: Saturday, April 27, 2019 7:46 PM
> 
> On Sat, Apr 27, 2019 at 10:10:29AM +0300, laurentiu.tudor@....com wrote:
> > From: Laurentiu Tudor <laurentiu.tudor@....com>
> >
> > The driver relies on the no longer valid assumption that dma addresses
> > (iovas) are identical to physical addressees and uses phys_to_virt() to
> > make iova -> vaddr conversions. Fix this by adding a function that does
> > proper iova -> phys conversions using the iommu api and update the code
> > to use it.
> > Also, a dma_unmap_single() call had to be moved further down the code
> > because iova -> vaddr conversions were required before the unmap.
> > For now only the contiguous frame case is handled and the SG case is
> > split in a following patch.
> > While at it, clean-up a redundant dpaa_bpid2pool() and pass the bp
> > as parameter.
> 
> Err, this is broken.  A driver using the DMA API has no business
> call IOMMU APIs.  Just save the _virtual_ address used for the mapping
> away and use that again.  We should not go through crazy gymnastics
> like this.

I think that due to the particularity of this hardware we don't have a way of saving the VA, but I'd let my colleagues maintaining this driver to comment more on why we need to do this.

---
Best Regards, Laurentiu