From: santosh.shilimkar@oracle.com
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Christoph Hellwig <hch@lst.de>
Cc: devicetree@vger.kernel.org,
Florian Fainelli <f.fainelli@gmail.com>,
linux-sh@vger.kernel.org, Frank Rowand <frowand.list@gmail.com>,
linux-usb@vger.kernel.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org,
iommu@lists.linux-foundation.org,
Rob Herring <robh+dt@kernel.org>,
Jim Quinlan <james.quinlan@broadcom.com>,
Santosh Shilimkar <ssantosh@kernel.org>,
Nathan Chancellor <natechancellor@gmail.com>,
Robin Murphy <robin.murphy@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/3] ARM/keystone: move the DMA offset handling under ifdef CONFIG_ARM_LPAE
Date: Fri, 11 Sep 2020 11:00:52 -0700 [thread overview]
Message-ID: <f13c72b9-9efa-7b9d-6c23-19f87b151bc4@oracle.com> (raw)
In-Reply-To: <20200911111551.GG1551@shell.armlinux.org.uk>
On 9/11/20 4:15 AM, Russell King - ARM Linux admin wrote:
> On Thu, Sep 10, 2020 at 07:40:37AM +0200, Christoph Hellwig wrote:
>> The DMA offset notifier can only be used if PHYS_OFFSET is at least
>> KEYSTONE_HIGH_PHYS_START, which can't be represented by a 32-bit
>> phys_addr_t. Currently the code compiles fine despite that, a pending
>> change to the DMA offset handling would create a compiler warning for
>> this case. Add an ifdef to not compile the code except for LPAE
>> configs.
>
> However, to have use of the high physical offset, LPAE needs to be
> enabled, which ensures that phys_addr_t is 64-bit.
>
> I believe that DMA is non-coherent on this platform unless the high
> physical address is used. Or something like that.
>
Exactly. Higher address ranges needs to be used for DMA coherency.
Regards,
Santosh
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next prev parent reply other threads:[~2020-09-11 18:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 5:40 support range based offsets in dma-direct Christoph Hellwig
2020-09-10 5:40 ` [PATCH 1/3] ARM/dma-mapping: move various helpers from dma-mapping.h to dma-direct.h Christoph Hellwig
2020-09-10 18:02 ` Robin Murphy
2020-09-11 6:25 ` Christoph Hellwig
2020-09-10 5:40 ` [PATCH 2/3] ARM/keystone: move the DMA offset handling under ifdef CONFIG_ARM_LPAE Christoph Hellwig
2020-09-11 11:12 ` Robin Murphy
2020-09-11 11:15 ` Russell King - ARM Linux admin
2020-09-11 11:27 ` Robin Murphy
2020-09-11 18:00 ` santosh.shilimkar [this message]
2020-09-10 5:40 ` [PATCH 3/3] dma-mapping: introduce DMA range map, supplanting dma_pfn_offset Christoph Hellwig
2020-09-10 7:53 ` Greg KH
2020-09-10 9:13 ` Christoph Hellwig
2020-09-10 16:12 ` Greg KH
2020-09-11 16:12 ` Robin Murphy
2020-09-12 6:46 ` Christoph Hellwig
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