linux-kernel - Re: [PATCH v2 2/2] x86/PCI: sta2x11: use default DMA address translation

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Message-ID: <51101de0f3b0fc5a3678c1ee0c723b131471f1b6.camel@suse.de>
Date:   Thu, 31 Oct 2019 11:43:40 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Christoph Hellwig <hch@...radead.org>, rubini <rubini@...dd.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, helgaas@...nel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 2/2] x86/PCI: sta2x11: use default DMA address
 translation

On Wed, 2019-10-30 at 14:45 -0700, Christoph Hellwig wrote:
> On Fri, Oct 18, 2019 at 01:00:44PM +0200, Nicolas Saenz Julienne wrote:
> > The devices found behind this PCIe chip have unusual DMA mapping
> > constraints as there is an AMBA interconnect placed in between them and
> > the different PCI endpoints. The offset between physical memory
> > addresses and AMBA's view is provided by reading a PCI config register,
> > which is saved and used whenever DMA mapping is needed.
> > 
> > It turns out that this DMA setup can be represented by properly setting
> > 'dma_pfn_offset', 'dma_bus_mask' and 'dma_mask' during the PCI device
> > enable fixup. And ultimately allows us to get rid of this device's
> > custom DMA functions.
> > 
> > Aside from the code deletion and DMA setup, sta2x11_pdev_to_mapping() is
> > moved to avoid warnings whenever CONFIG_PM is not enabled.
> 
> Looks sensible to me:
> 
> Reviewed-by: Christoph Hellwig <hch@....de>
> 
> But I can't tested it either, and kinda wonder if this code is actually
> still used by anyone..

Maybe Alessandro can shine some light on this (though I wonder his mail is stil
valid).


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