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Date: Thu, 21 Dec 2023 21:05:49 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Ajay Agarwal <ajayagarwal@google.com>
Cc: Jingoo Han <jingoohan1@gmail.com>,
	Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
	Rob Herring <robh@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	Manu Gautam <manugautam@google.com>,
	Sajid Dalvi <sdalvi@google.com>,
	William McVicker <willmcvicker@google.com>,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH] PCI: dwc: Set DMA mask to 32 only if ZONE_DMA32 is
 enabled
Message-ID: <ZYUZLRczqgzO7Gf4@infradead.org>
References: <20231221174051.35420-1-ajayagarwal@google.com>
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On Thu, Dec 21, 2023 at 11:10:51PM +0530, Ajay Agarwal wrote:
> If CONFIG_ZONE_DMA32 is disabled, then the dmam_alloc_coherent
> will fail to allocate the memory if there are no 32-bit addresses
> available. This will lead to the PCIe RC probe failure.
> Fix this by setting the DMA mask to 32 bits only if the kernel
> configuration enables DMA32 zone. Else, leave the mask as is.

And that's why you never must disable ZONE_DMA32 on devices that
can have more than >32bit memory and don't use an iommu for
everything.

NAK.