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

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Message-ID: <20191030214548.GC25515@infradead.org>
Date:   Wed, 30 Oct 2019 14:45:48 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     rubini@...dd.com, hch@...radead.org, 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 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..