Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Christoph Hellwig]

On Thu, Jan 04, 2018 at 09:49:30AM +0100, Christoph Hellwig wrote:
> On Tue, Jan 02, 2018 at 08:45:30PM +1100, Michael Ellerman wrote:
> > Christoph Hellwig  writes:
> > 
> > > We want to use the dma_direct_ namespace for a generic implementation,
> > > so rename powerpc to the second best choice: dma_nommu_.
> > 
> > I'm not a fan of "nommu". Some of the users of direct ops *are* using an
> > IOMMU, they're just setting up a 1:1 mapping once at init time, rather
> > than mapping dynamically.
> > 
> > Though I don't have a good idea for a better name, maybe "1to1",
> > "linear", "premapped" ?
> 
> It seems like a nice counter part to the dma_iommu_ops used just about
> anywhere else in ppc.
> 
> But I'll happily take any maintainer bike shed decision for the next
> series.  Remember that in a merge window or two it will hopefully
> go away in favor of the new generic dma_direct ops.

Michael, please suggest what name you want for the next iteration,
I don't want to hold up the series on a naming bikeshed.
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Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Christoph Hellwig]

On Tue, Jan 02, 2018 at 08:45:30PM +1100, Michael Ellerman wrote:
> Christoph Hellwig  writes:
> 
> > We want to use the dma_direct_ namespace for a generic implementation,
> > so rename powerpc to the second best choice: dma_nommu_.
> 
> I'm not a fan of "nommu". Some of the users of direct ops *are* using an
> IOMMU, they're just setting up a 1:1 mapping once at init time, rather
> than mapping dynamically.
> 
> Though I don't have a good idea for a better name, maybe "1to1",
> "linear", "premapped" ?

It seems like a nice counter part to the dma_iommu_ops used just about
anywhere else in ppc.

But I'll happily take any maintainer bike shed decision for the next
series.  Remember that in a merge window or two it will hopefully
go away in favor of the new generic dma_direct ops.
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Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Christoph Hellwig]

On Wed, Jan 03, 2018 at 07:19:46PM +1100, Julian Calaby wrote:
> If this is indeed a linear mapping, can we just remove this and
> replace it with the new "generic" mapping being introduced by this
> patchset?

That is the long-term plan.  But as the powerpc one includes support
for non-coherent DMA it will have to wait for the next batch.
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Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Julian Calaby]

Hi All,

On Wed, Jan 3, 2018 at 6:49 PM, Geert Uytterhoeven  wrote:
> Hi Michael,
>
> On Wed, Jan 3, 2018 at 7:24 AM, Michael Ellerman  wrote:
>> Geert Uytterhoeven  writes:
>>
>>> On Tue, Jan 2, 2018 at 10:45 AM, Michael Ellerman  
>>> wrote:
 Christoph Hellwig  writes:

> We want to use the dma_direct_ namespace for a generic implementation,
> so rename powerpc to the second best choice: dma_nommu_.

 I'm not a fan of "nommu". Some of the users of direct ops *are* using an
 IOMMU, they're just setting up a 1:1 mapping once at init time, rather
 than mapping dynamically.

 Though I don't have a good idea for a better name, maybe "1to1",
 "linear", "premapped" ?
>>>
>>> "identity"?
>>
>> I think that would be wrong, but thanks for trying to help :)
>>
>> The address on the device side is sometimes (often?) offset from the CPU
>> address. So eg. the device can DMA to RAM address 0x0 using address
>> 0x800.
>>
>> Identity would imply 0 == 0 etc.
>>
>> I think "bijective" is the correct term, but that's probably a bit
>> esoteric.
>
> OK, didn't know about the offset.
> Then "linear" is what we tend to use, right?

If this is indeed a linear mapping, can we just remove this and
replace it with the new "generic" mapping being introduced by this
patchset?

Thanks,

-- 
Julian Calaby

Email: julian.cal...@gmail.com
Profile: http://www.google.com/profiles/julian.calaby/
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Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Geert Uytterhoeven]

Hi Michael,

On Wed, Jan 3, 2018 at 7:24 AM, Michael Ellerman  wrote:
> Geert Uytterhoeven  writes:
>
>> On Tue, Jan 2, 2018 at 10:45 AM, Michael Ellerman  
>> wrote:
>>> Christoph Hellwig  writes:
>>>
 We want to use the dma_direct_ namespace for a generic implementation,
 so rename powerpc to the second best choice: dma_nommu_.
>>>
>>> I'm not a fan of "nommu". Some of the users of direct ops *are* using an
>>> IOMMU, they're just setting up a 1:1 mapping once at init time, rather
>>> than mapping dynamically.
>>>
>>> Though I don't have a good idea for a better name, maybe "1to1",
>>> "linear", "premapped" ?
>>
>> "identity"?
>
> I think that would be wrong, but thanks for trying to help :)
>
> The address on the device side is sometimes (often?) offset from the CPU
> address. So eg. the device can DMA to RAM address 0x0 using address
> 0x800.
>
> Identity would imply 0 == 0 etc.
>
> I think "bijective" is the correct term, but that's probably a bit
> esoteric.

OK, didn't know about the offset.
Then "linear" is what we tend to use, right?

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Michael Ellerman]

Geert Uytterhoeven  writes:

> On Tue, Jan 2, 2018 at 10:45 AM, Michael Ellerman  wrote:
>> Christoph Hellwig  writes:
>>
>>> We want to use the dma_direct_ namespace for a generic implementation,
>>> so rename powerpc to the second best choice: dma_nommu_.
>>
>> I'm not a fan of "nommu". Some of the users of direct ops *are* using an
>> IOMMU, they're just setting up a 1:1 mapping once at init time, rather
>> than mapping dynamically.
>>
>> Though I don't have a good idea for a better name, maybe "1to1",
>> "linear", "premapped" ?
>
> "identity"?

I think that would be wrong, but thanks for trying to help :)

The address on the device side is sometimes (often?) offset from the CPU
address. So eg. the device can DMA to RAM address 0x0 using address
0x800.

Identity would imply 0 == 0 etc.

I think "bijective" is the correct term, but that's probably a bit
esoteric.

cheers
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Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Michael Ellerman]

Christoph Hellwig  writes:

> We want to use the dma_direct_ namespace for a generic implementation,
> so rename powerpc to the second best choice: dma_nommu_.

I'm not a fan of "nommu". Some of the users of direct ops *are* using an
IOMMU, they're just setting up a 1:1 mapping once at init time, rather
than mapping dynamically.

Though I don't have a good idea for a better name, maybe "1to1",
"linear", "premapped" ?

cheers
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