linux-kernel - RE: [PATCH] ata: ahci_platform: add 32-bit quirk for dwc-ahci

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Date:   Wed, 12 Feb 2020 11:56:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Robin Murphy' <robin.murphy@....com>,
        Hans de Goede <hdegoede@...hat.com>,
        Roger Quadros <rogerq@...com>,
        "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "vigneshr@...com" <vigneshr@...com>,
        "nsekhar@...com" <nsekhar@...com>,
        "linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Péter Ujfalusi <peter.ujfalusi@...com>
Subject: RE: [PATCH] ata: ahci_platform: add 32-bit quirk for dwc-ahci

From: Robin Murphy
> Sent: 12 February 2020 11:43
...
> If the device *is* inherently 64-bit capable, then setting 64-bit masks
> in the driver is correct - if a 64-bit IP block happens to have been
> integrated with only 32 address bits wired up, but the system has memory
> above the 32-bit boundary, then that should be described via
> "dma-ranges", which should then end up being used to further constrain
> the device masks internally to the DMA API.

Given how often this happens (please can I shoot some more
hardware engineers - he says while compiling some VHDL)
is it possible to allocate some memory pages that are
aliases if the address bits over 31 are ignored?

Then (at least some) drivers could to a run-time probe
reading to the high address and checking the data didn't
appear in the low address.

Only one such set of pages is needed - access can be locked.
But they'd need to be reserved early on.

	David

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