* question about dma-ranges
@ 2010-10-27 0:48 Yoder Stuart-B08248
[not found] ` <9696D7A991D0824DBA8DFAC74A9C5FA306911C5F-ofAVchDyotYzzZk0BCvKg5jmvxFtTJ+o0e7PPNI6Mm0@public.gmane.org>
0 siblings, 1 reply; 6+ messages in thread
From: Yoder Stuart-B08248 @ 2010-10-27 0:48 UTC (permalink / raw)
To: Mitch Bradley; +Cc: devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ
Mitch,
In the dma-ranges proposal:
http://playground.sun.com/1275/proposals/Closed/Accepted/410-it.txt
...there is the following special case described:
As a special case, a "dma-ranges" property may be present in the
root node of the device tree. In this case, the property value
describes the ranges of DMA addresses that the system bus can
accept. In this case, the length of the parent-address portion
of each entry in the property value is 0 (because the root node
has no parent), so the format reduces to...
A few of us in the ePAPR committee were discussing this and
were wondering what the use case for a dma-ranges on the
root is. Is this special case really needed?
Thanks,
Stuart Yoder
^ permalink raw reply [flat|nested] 6+ messages in thread[parent not found: <9696D7A991D0824DBA8DFAC74A9C5FA306911C5F-ofAVchDyotYzzZk0BCvKg5jmvxFtTJ+o0e7PPNI6Mm0@public.gmane.org>]
* Re: question about dma-ranges [not found] ` <9696D7A991D0824DBA8DFAC74A9C5FA306911C5F-ofAVchDyotYzzZk0BCvKg5jmvxFtTJ+o0e7PPNI6Mm0@public.gmane.org> @ 2010-10-27 0:51 ` Mitch Bradley [not found] ` <4CC77784.2070701-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org> 0 siblings, 1 reply; 6+ messages in thread From: Mitch Bradley @ 2010-10-27 0:51 UTC (permalink / raw) To: Yoder Stuart-B08248; +Cc: devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ It's probably unnecessary on modern machines, but old PCs were fairly restrictive about DMA addresses due to short counters. The buses on which such restrictions applied are no longer at the root level, but they were once there... On 10/27/2010 8:48 AM, Yoder Stuart-B08248 wrote: > Mitch, > > In the dma-ranges proposal: > > http://playground.sun.com/1275/proposals/Closed/Accepted/410-it.txt > > ...there is the following special case described: > > As a special case, a "dma-ranges" property may be present in the > root node of the device tree. In this case, the property value > describes the ranges of DMA addresses that the system bus can > accept. In this case, the length of the parent-address portion > of each entry in the property value is 0 (because the root node > has no parent), so the format reduces to... > > A few of us in the ePAPR committee were discussing this and > were wondering what the use case for a dma-ranges on the > root is. Is this special case really needed? > > Thanks, > Stuart Yoder > > > ^ permalink raw reply [flat|nested] 6+ messages in thread
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* Re: question about dma-ranges [not found] ` <4CC77784.2070701-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org> @ 2010-10-27 1:37 ` Timur Tabi [not found] ` <AANLkTikTu_p0-Uk7=FuUay4mvCEEU0e9V5eY6bjuK5RQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 0 siblings, 1 reply; 6+ messages in thread From: Timur Tabi @ 2010-10-27 1:37 UTC (permalink / raw) To: Mitch Bradley Cc: Yoder Stuart-B08248, devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ On Tue, Oct 26, 2010 at 7:51 PM, Mitch Bradley <wmb-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org> wrote: > It's probably unnecessary on modern machines, but old PCs were fairly > restrictive about DMA addresses due to short counters. The buses on which > such restrictions applied are no longer at the root level, but they were > once there... It's still necessary. The QE, which we ship on several of our current parts, can only DMA to/from 32-bit addresses, even on SOCs that support 36-bit addressing for everything else. -- Timur Tabi Linux kernel developer at Freescale ^ permalink raw reply [flat|nested] 6+ messages in thread
[parent not found: <AANLkTikTu_p0-Uk7=FuUay4mvCEEU0e9V5eY6bjuK5RQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>]
* Re: question about dma-ranges [not found] ` <AANLkTikTu_p0-Uk7=FuUay4mvCEEU0e9V5eY6bjuK5RQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> @ 2010-10-27 2:42 ` David Gibson 2010-10-27 19:46 ` Scott Wood 0 siblings, 1 reply; 6+ messages in thread From: David Gibson @ 2010-10-27 2:42 UTC (permalink / raw) To: Timur Tabi; +Cc: Yoder Stuart-B08248, devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ On Tue, Oct 26, 2010 at 08:37:55PM -0500, Timur Tabi wrote: > On Tue, Oct 26, 2010 at 7:51 PM, Mitch Bradley <wmb-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org> wrote: > > It's probably unnecessary on modern machines, but old PCs were fairly > > restrictive about DMA addresses due to short counters. The buses on which > > such restrictions applied are no longer at the root level, but they were > > once there... > > It's still necessary. The QE, which we ship on several of our current > parts, can only DMA to/from 32-bit addresses, even on SOCs that > support 36-bit addressing for everything else. But the QE is not at the top-level, IIRC, so its restrictions can be encoded in the dma-ranges on its own bus. We're talking specifically about the special case of dma-ranges in the root node, not the utility of dma-ranges in general which is clear. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: question about dma-ranges 2010-10-27 2:42 ` David Gibson @ 2010-10-27 19:46 ` Scott Wood [not found] ` <20101027144602.2c5ef098-N/eSCTBpGwP7j4BuCOFQISmX4OfbXNuMKnGXBo5VDl8@public.gmane.org> 0 siblings, 1 reply; 6+ messages in thread From: Scott Wood @ 2010-10-27 19:46 UTC (permalink / raw) To: David Gibson Cc: Yoder Stuart-B08248, devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ, Timur Tabi On Wed, 27 Oct 2010 13:42:27 +1100 David Gibson <david@gibson.dropbear.id.au> wrote: > On Tue, Oct 26, 2010 at 08:37:55PM -0500, Timur Tabi wrote: > > On Tue, Oct 26, 2010 at 7:51 PM, Mitch Bradley <wmb@firmworks.com> wrote: > > > It's probably unnecessary on modern machines, but old PCs were fairly > > > restrictive about DMA addresses due to short counters. The buses on which > > > such restrictions applied are no longer at the root level, but they were > > > once there... > > > > It's still necessary. The QE, which we ship on several of our current > > parts, can only DMA to/from 32-bit addresses, even on SOCs that > > support 36-bit addressing for everything else. > > But the QE is not at the top-level, IIRC, so its restrictions can be > encoded in the dma-ranges on its own bus. We're talking specifically > about the special case of dma-ranges in the root node, not the utility > of dma-ranges in general which is clear. Plus, in this case does that need to be expressed in the device tree? Or can the QE code just know about that because it only has 32-bit registers/descriptor fields for DMA addresses? I.e. it is a limitation of all instances of QE, not just as integrated in this system. -Scott _______________________________________________ devicetree-discuss mailing list devicetree-discuss@lists.ozlabs.org https://lists.ozlabs.org/listinfo/devicetree-discuss ^ permalink raw reply [flat|nested] 6+ messages in thread
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* Re: question about dma-ranges [not found] ` <20101027144602.2c5ef098-N/eSCTBpGwP7j4BuCOFQISmX4OfbXNuMKnGXBo5VDl8@public.gmane.org> @ 2010-10-27 19:47 ` Timur Tabi 0 siblings, 0 replies; 6+ messages in thread From: Timur Tabi @ 2010-10-27 19:47 UTC (permalink / raw) To: Scott Wood; +Cc: Yoder Stuart-B08248, devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ Scott Wood wrote: > Or can the QE code just know about that because it only has 32-bit > registers/descriptor fields for DMA addresses? I.e. it is a limitation > of all instances of QE, not just as integrated in this system. It's a limitation of the QE registers -- they're only 32-bit. If we ever produce a new QE that has bigger registers, we can use the compatible property to distinguish between them. -- Timur Tabi Linux kernel developer at Freescale ^ permalink raw reply [flat|nested] 6+ messages in thread
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2010-10-27 0:48 question about dma-ranges Yoder Stuart-B08248
[not found] ` <9696D7A991D0824DBA8DFAC74A9C5FA306911C5F-ofAVchDyotYzzZk0BCvKg5jmvxFtTJ+o0e7PPNI6Mm0@public.gmane.org>
2010-10-27 0:51 ` Mitch Bradley
[not found] ` <4CC77784.2070701-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org>
2010-10-27 1:37 ` Timur Tabi
[not found] ` <AANLkTikTu_p0-Uk7=FuUay4mvCEEU0e9V5eY6bjuK5RQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-10-27 2:42 ` David Gibson
2010-10-27 19:46 ` Scott Wood
[not found] ` <20101027144602.2c5ef098-N/eSCTBpGwP7j4BuCOFQISmX4OfbXNuMKnGXBo5VDl8@public.gmane.org>
2010-10-27 19:47 ` Timur Tabi
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