linux-kernel - Re: [PATCH v3 0/4] PCI: get DMA configuration from parent device

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Message-ID: <54AF08C7.2010100@ti.com>
Date:	Thu, 8 Jan 2015 17:46:31 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<bhelgaas@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
	<joro@...tes.org>, <grant.likely@...aro.org>, <robh+dt@...nel.org>,
	<iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<will.deacon@....com>, <linux@....linux.org.uk>
Subject: Re: [PATCH v3 0/4] PCI: get DMA configuration from parent device

On 01/08/2015 05:27 PM, Arnd Bergmann wrote:
> On Thursday 08 January 2015 09:56:39 Arnd Bergmann wrote:
>> There is another interesting case, which is a USB host controller or
>> something similar behind a PCI bus. These are quite common and also
>> need to be handled in some form. Let's do just PCI first for now, but
>> be aware that this will come next. Should we assume that the ID that
>> is required for a device is either known from the device node, or
>> that it comes from a PCI device? That means for the USB case, we will
>> likely need to have some custom logic. There seems to be an implicit
>> assumption all over the kernel that all devices have the same IOMMU
>> instance, but we can't really rely on that here.
>>
>
> Update: I've checked the USB implementation and we are lucky because
> these interactions are all done by the USB host controller, and a
> USB device is not itself DMA capable. We don't have to do anything
> for USB.

Ok Thanks.

Murali
>
> 	Arnd
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-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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