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Date:   Fri, 9 Sep 2022 06:29:50 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Will McVicker <willmcvicker@google.com>
Cc:     Jingoo Han <jingoohan1@gmail.com>,
        Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
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Subject: Re: [PATCH v5 2/2] PCI: dwc: Add support for 64-bit MSI target
 address
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 <20220825185026.3816331-3-willmcvicker@google.com>
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On Thu, Aug 25, 2022 at 06:50:25PM +0000, Will McVicker wrote:
> Since not all devices require a 32-bit MSI address, add support to the
> PCIe host driver to allow setting the DMA mask to 64-bits if the 32-bit
> allocation fails. This allows kernels to disable ZONE_DMA32 and bounce
> buffering (swiotlb) without risking not being able to get a 32-bit address
> during DMA allocation.

Umm.  You can't just disable ZONE_DMA32.  Linux absolutely requires a
32-bit dma mask to work, it is in fact the implicit default.