Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory()

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory()

[Guennadi Liakhovetski]

On Thu, 26 Aug 2010, FUJITA Tomonori wrote:

> On Thu, 26 Aug 2010 09:04:14 +0300
> Marin Mitov <mitov@issp.bas.bg> wrote:
> 
> > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote:
> > > On Fri, 20 Aug 2010 14:50:12 +0300
> > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > 
> > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote:
> > > > > On Fri, 20 Aug 2010 11:13:45 +0300
> > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > 
> > > > > > > > This tric is already used in drivers/staging/dt3155v4l.c
> > > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent()
> > > > > > > > 
> > > > > > > > Here proposed for general use by popular demand from video4linux folks.
> > > > > > > > Helps for videobuf-dma-contig framework.
> > > > > > > 
> > > > > > > What you guys exactly want to do? If you just want to pre-allocate
> > > > > > > coherent memory for latter usage,
> > > > > > 
> > > > > > Yes, just to preallocate not coherent, but rather contiguous memory for latter usage.
> > > > > > We use coherent memory because it turns out to be contiguous.
> > > > > 
> > > > > Hmm, you don't care about coherency? You just need contiguous memory?
> > > > 
> > > > Yes. We just need contiguous memory. Coherency is important as far as when dma
> > > > transfer finishes user land is able to see the new data. Could be done by something like
> > > > dma_{,un}map_single()
> > > 
> > > Then, we should avoid using coherent memory as I exaplained before. In
> > > addition, dma_alloc_coherent can't provide large enough contigous
> > > memory for some drivers so this patch doesn't help much.
> > 
> > Please, look at drivers/media/video/videobuf-dma-contig.c. Using coherent memory
> > is inavoidable for now, there is no alternative for it for now. The two new functions,
> > which I propose are just helpers for those of us who already use coherent memory
> > (via videobuf-dma-contig API). May be adding these two functions to 
> > drivers/media/video/videobuf-dma-contig.c will be better solution?
> 
> If you add something to the videobuf-dma-contig API, that's fine by me
> because drivers/media/video/videobuf-dma-contig.c uses the own
> structure and plays with dma_alloc_coherent. As long as a driver
> doesn't touch device->dma_mem directly, it's fine, I think (that is,
> dt3155v4l driver is broken). There are already some workarounds for
> contigous memory in several drivers anyway.

No, this will not work - this API has to be used from board code and 
videobuf can be built modular.

> We will have the proper API for contiguous memory. I don't think that
> adding such workaround to the DMA API is a good idea.

We have currently a number of boards broken in the mainline. They must be 
fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
as I suggested earlier, we need either this or my patch series

http://thread.gmane.org/gmane.linux.ports.sh.devel/8595

for 2.6.36.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Re: [RFC][PATCH] add

[@ 2010-08-26 9:17 UTC (permalink / raw)]

Hello,

On Thu, Aug 26, 2010 at 11:06:20AM +0200, Guennadi Liakhovetski wrote:
> On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> 
> > On Thu, 26 Aug 2010 09:04:14 +0300
> > Marin Mitov <mitov@issp.bas.bg> wrote:
> > 
> > > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote:
> > > > On Fri, 20 Aug 2010 14:50:12 +0300
> > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > 
> > > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote:
> > > > > > On Fri, 20 Aug 2010 11:13:45 +0300
> > > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > > 
> > > > > > > > > This tric is already used in drivers/staging/dt3155v4l.c
> > > > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent()
> > > > > > > > > 
> > > > > > > > > Here proposed for general use by popular demand from video4linux folks.
> > > > > > > > > Helps for videobuf-dma-contig framework.
> > > > > > > > 
> > > > > > > > What you guys exactly want to do? If you just want to pre-allocate
> > > > > > > > coherent memory for latter usage,
> > > > > > > 
> > > > > > > Yes, just to preallocate not coherent, but rather contiguous memory for latter usage.
> > > > > > > We use coherent memory because it turns out to be contiguous.
> > > > > > 
> > > > > > Hmm, you don't care about coherency? You just need contiguous memory?
> > > > > 
> > > > > Yes. We just need contiguous memory. Coherency is important as far as when dma
> > > > > transfer finishes user land is able to see the new data. Could be done by something like
> > > > > dma_{,un}map_single()
> > > > 
> > > > Then, we should avoid using coherent memory as I exaplained before. In
> > > > addition, dma_alloc_coherent can't provide large enough contigous
> > > > memory for some drivers so this patch doesn't help much.
> > > 
> > > Please, look at drivers/media/video/videobuf-dma-contig.c. Using coherent memory
> > > is inavoidable for now, there is no alternative for it for now. The two new functions,
> > > which I propose are just helpers for those of us who already use coherent memory
> > > (via videobuf-dma-contig API). May be adding these two functions to 
> > > drivers/media/video/videobuf-dma-contig.c will be better solution?
> > 
> > If you add something to the videobuf-dma-contig API, that's fine by me
> > because drivers/media/video/videobuf-dma-contig.c uses the own
> > structure and plays with dma_alloc_coherent. As long as a driver
> > doesn't touch device->dma_mem directly, it's fine, I think (that is,
> > dt3155v4l driver is broken). There are already some workarounds for
> > contigous memory in several drivers anyway.
> 
> No, this will not work - this API has to be used from board code and 
> videobuf can be built modular.
> 
> > We will have the proper API for contiguous memory. I don't think that
> > adding such workaround to the DMA API is a good idea.
> 
> We have currently a number of boards broken in the mainline. They must be 
> fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> as I suggested earlier, we need either this or my patch series
> 
> http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
this seems to be more mature to me.  The original patch in this thread
uses a symbol DT3155_COH_FLAGS which seems misplaced in generic code and
doesn't put the new functions in a header.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Marin Mitov]

On Thursday, August 26, 2010 12:17:25 pm Uwe Kleine-König wrote:
> Hello,
> 
> On Thu, Aug 26, 2010 at 11:06:20AM +0200, Guennadi Liakhovetski wrote:
> > On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> > 
> > > On Thu, 26 Aug 2010 09:04:14 +0300
> > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > 
> > > > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote:
> > > > > On Fri, 20 Aug 2010 14:50:12 +0300
> > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > 
> > > > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote:
> > > > > > > On Fri, 20 Aug 2010 11:13:45 +0300
> > > > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > > > 
> > > > > > > > > > This tric is already used in drivers/staging/dt3155v4l.c
> > > > > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent()
> > > > > > > > > > 
> > > > > > > > > > Here proposed for general use by popular demand from video4linux folks.
> > > > > > > > > > Helps for videobuf-dma-contig framework.
> > > > > > > > > 
> > > > > > > > > What you guys exactly want to do? If you just want to pre-allocate
> > > > > > > > > coherent memory for latter usage,
> > > > > > > > 
> > > > > > > > Yes, just to preallocate not coherent, but rather contiguous memory for latter usage.
> > > > > > > > We use coherent memory because it turns out to be contiguous.
> > > > > > > 
> > > > > > > Hmm, you don't care about coherency? You just need contiguous memory?
> > > > > > 
> > > > > > Yes. We just need contiguous memory. Coherency is important as far as when dma
> > > > > > transfer finishes user land is able to see the new data. Could be done by something like
> > > > > > dma_{,un}map_single()
> > > > > 
> > > > > Then, we should avoid using coherent memory as I exaplained before. In
> > > > > addition, dma_alloc_coherent can't provide large enough contigous
> > > > > memory for some drivers so this patch doesn't help much.
> > > > 
> > > > Please, look at drivers/media/video/videobuf-dma-contig.c. Using coherent memory
> > > > is inavoidable for now, there is no alternative for it for now. The two new functions,
> > > > which I propose are just helpers for those of us who already use coherent memory
> > > > (via videobuf-dma-contig API). May be adding these two functions to 
> > > > drivers/media/video/videobuf-dma-contig.c will be better solution?
> > > 
> > > If you add something to the videobuf-dma-contig API, that's fine by me
> > > because drivers/media/video/videobuf-dma-contig.c uses the own
> > > structure and plays with dma_alloc_coherent. As long as a driver
> > > doesn't touch device->dma_mem directly, it's fine, I think (that is,
> > > dt3155v4l driver is broken). There are already some workarounds for
> > > contigous memory in several drivers anyway.
> > 
> > No, this will not work - this API has to be used from board code and 
> > videobuf can be built modular.
> > 
> > > We will have the proper API for contiguous memory. I don't think that
> > > adding such workaround to the DMA API is a good idea.
> > 
> > We have currently a number of boards broken in the mainline. They must be 
> > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > as I suggested earlier, we need either this or my patch series
> > 
> > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> this seems to be more mature to me.  The original patch in this thread
> uses a symbol DT3155_COH_FLAGS which seems misplaced in generic code and
> doesn't put the new functions in a header.

You are right. DT3155_COH_FLAGS should be defined, and a declaration should be 
put in the headers.

But it is just RFC :-)

Marin Mitov

> 
> Best regards
> Uwe
> 
> 

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Thu, 26 Aug 2010 11:06:20 +0200 (CEST)
Guennadi Liakhovetski <g.liakhovetski@gmx.de> wrote:

> On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> 
> > On Thu, 26 Aug 2010 09:04:14 +0300
> > Marin Mitov <mitov@issp.bas.bg> wrote:
> > 
> > > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote:
> > > > On Fri, 20 Aug 2010 14:50:12 +0300
> > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > 
> > > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote:
> > > > > > On Fri, 20 Aug 2010 11:13:45 +0300
> > > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > > 
> > > > > > > > > This tric is already used in drivers/staging/dt3155v4l.c
> > > > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent()
> > > > > > > > > 
> > > > > > > > > Here proposed for general use by popular demand from video4linux folks.
> > > > > > > > > Helps for videobuf-dma-contig framework.
> > > > > > > > 
> > > > > > > > What you guys exactly want to do? If you just want to pre-allocate
> > > > > > > > coherent memory for latter usage,
> > > > > > > 
> > > > > > > Yes, just to preallocate not coherent, but rather contiguous memory for latter usage.
> > > > > > > We use coherent memory because it turns out to be contiguous.
> > > > > > 
> > > > > > Hmm, you don't care about coherency? You just need contiguous memory?
> > > > > 
> > > > > Yes. We just need contiguous memory. Coherency is important as far as when dma
> > > > > transfer finishes user land is able to see the new data. Could be done by something like
> > > > > dma_{,un}map_single()
> > > > 
> > > > Then, we should avoid using coherent memory as I exaplained before. In
> > > > addition, dma_alloc_coherent can't provide large enough contigous
> > > > memory for some drivers so this patch doesn't help much.
> > > 
> > > Please, look at drivers/media/video/videobuf-dma-contig.c. Using coherent memory
> > > is inavoidable for now, there is no alternative for it for now. The two new functions,
> > > which I propose are just helpers for those of us who already use coherent memory
> > > (via videobuf-dma-contig API). May be adding these two functions to 
> > > drivers/media/video/videobuf-dma-contig.c will be better solution?
> > 
> > If you add something to the videobuf-dma-contig API, that's fine by me
> > because drivers/media/video/videobuf-dma-contig.c uses the own
> > structure and plays with dma_alloc_coherent. As long as a driver
> > doesn't touch device->dma_mem directly, it's fine, I think (that is,
> > dt3155v4l driver is broken). There are already some workarounds for
> > contigous memory in several drivers anyway.
> 
> No, this will not work - this API has to be used from board code and 
> videobuf can be built modular.
> 
> > We will have the proper API for contiguous memory. I don't think that
> > adding such workaround to the DMA API is a good idea.
> 
> We have currently a number of boards broken in the mainline. They must be 
> fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> as I suggested earlier, we need either this or my patch series
> 
> http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> 
> for 2.6.36.

Why can't you revert a commit that causes the regression?

The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
responsible for the regression. And the patchset even exnteds the
definition of the DMA API (dma_declare_coherent_memory). Such change
shouldn't applied after rc1. I think that DMA-API.txt says that
dma_declare_coherent_memory() handles coherent memory for a particular
device. It's not for the API that reserves coherent memory that can be
used for any device for a single device.

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory()

[Guennadi Liakhovetski]

On Thu, 26 Aug 2010, FUJITA Tomonori wrote:

> Why can't you revert a commit that causes the regression?

See this reply, and the complete thread too.

http://marc.info/?l=linux-sh&m\x128130485208262&w=2

> The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> responsible for the regression. And the patchset even exnteds the
> definition of the DMA API (dma_declare_coherent_memory). Such change
> shouldn't applied after rc1. I think that DMA-API.txt says that
> dma_declare_coherent_memory() handles coherent memory for a particular
> device. It's not for the API that reserves coherent memory that can be
> used for any device for a single device.

Anyway, we need a way to fix the regression.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Thu, 26 Aug 2010 11:45:58 +0200 (CEST)
Guennadi Liakhovetski <g.liakhovetski@gmx.de> wrote:

> On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> 
> > Why can't you revert a commit that causes the regression?
> 
> See this reply, and the complete thread too.
> 
> http://marc.info/?l=linux-sh&m\x128130485208262&w=2
> 
> > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > responsible for the regression. And the patchset even exnteds the
> > definition of the DMA API (dma_declare_coherent_memory). Such change
> > shouldn't applied after rc1. I think that DMA-API.txt says that
> > dma_declare_coherent_memory() handles coherent memory for a particular
> > device. It's not for the API that reserves coherent memory that can be
> > used for any device for a single device.
> 
> Anyway, we need a way to fix the regression.

Needs to find a different way.

Re: [RFC][PATCH] add

[Russell King - ARM Linux]

On Thu, Aug 26, 2010 at 06:51:48PM +0900, FUJITA Tomonori wrote:
> On Thu, 26 Aug 2010 11:45:58 +0200 (CEST)
> Guennadi Liakhovetski <g.liakhovetski@gmx.de> wrote:
> 
> > On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> > 
> > > Why can't you revert a commit that causes the regression?
> > 
> > See this reply, and the complete thread too.
> > 
> > http://marc.info/?l=linux-sh&m\x128130485208262&w=2
> > 
> > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > responsible for the regression. And the patchset even exnteds the
> > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > device. It's not for the API that reserves coherent memory that can be
> > > used for any device for a single device.
> > 
> > Anyway, we need a way to fix the regression.
> 
> Needs to find a different way.

No.  ioremap on memory mapped by the kernel is just plain not permitted
with ARMv6 and ARMv7 architectures.

It's not something you can say "oh, need to find another way" because there
is _no_ software solution to having physical regions mapped multiple times
with different attributes.  It's an architectural restriction.

We can't unmap the kernel's memory mapping either, as I've already explained
several times this month - and I'm getting frustrated at having to keep
on explaining that point.

Just accept the plain fact that multiple mappings of the same physical
regions have become illegal.

What we need is another alternative other than using ioremap on memory
already mapped by the kernel - eg, by reserving a certain chunk of
memory for this purpose at boot time which his _never_ mapped by the
kernel, except via ioremap.

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Marin Mitov]

On Thursday, August 26, 2010 08:49:09 pm Russell King - ARM Linux wrote:
> On Thu, Aug 26, 2010 at 06:51:48PM +0900, FUJITA Tomonori wrote:
> > On Thu, 26 Aug 2010 11:45:58 +0200 (CEST)
> > Guennadi Liakhovetski <g.liakhovetski@gmx.de> wrote:
> > 
> > > On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> > > 
> > > > Why can't you revert a commit that causes the regression?
> > > 
> > > See this reply, and the complete thread too.
> > > 
> > > http://marc.info/?l=linux-sh&m\x128130485208262&w=2
> > > 
> > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > responsible for the regression. And the patchset even exnteds the
> > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > device. It's not for the API that reserves coherent memory that can be
> > > > used for any device for a single device.
> > > 
> > > Anyway, we need a way to fix the regression.
> > 
> > Needs to find a different way.
> 
> No.  ioremap on memory mapped by the kernel is just plain not permitted
> with ARMv6 and ARMv7 architectures.

Hi Russell,

Just because ioremap on memory mapped by the kernel is just plain not permitted
I have proposed a new pair of functions: dma_reserve_coherent_memory()/dma_free_reserved_memory()

http://lkml.org/lkml/2010/8/19/200

but it is not quite well accepted from the community.
What is your opinion?

Thanks,

Marin Mitov

> 
> It's not something you can say "oh, need to find another way" because there
> is _no_ software solution to having physical regions mapped multiple times
> with different attributes.  It's an architectural restriction.
> 
> We can't unmap the kernel's memory mapping either, as I've already explained
> several times this month - and I'm getting frustrated at having to keep
> on explaining that point.
> 
> Just accept the plain fact that multiple mappings of the same physical
> regions have become illegal.
> 
> What we need is another alternative other than using ioremap on memory
> already mapped by the kernel - eg, by reserving a certain chunk of
> memory for this purpose at boot time which his _never_ mapped by the
> kernel, except via ioremap.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [RFC][PATCH] add

[@ 2010-08-26 9:53 UTC (permalink / raw)]

On Thu, Aug 26, 2010 at 06:30:02PM +0900, FUJITA Tomonori wrote:
> On Thu, 26 Aug 2010 11:06:20 +0200 (CEST)
> Guennadi Liakhovetski <g.liakhovetski@gmx.de> wrote:
> 
> > On Thu, 26 Aug 2010, FUJITA Tomonori wrote:
> > 
> > > On Thu, 26 Aug 2010 09:04:14 +0300
> > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > 
> > > > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote:
> > > > > On Fri, 20 Aug 2010 14:50:12 +0300
> > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > 
> > > > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote:
> > > > > > > On Fri, 20 Aug 2010 11:13:45 +0300
> > > > > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > > > > > 
> > > > > > > > > > This tric is already used in drivers/staging/dt3155v4l.c
> > > > > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent()
> > > > > > > > > > 
> > > > > > > > > > Here proposed for general use by popular demand from video4linux folks.
> > > > > > > > > > Helps for videobuf-dma-contig framework.
> > > > > > > > > 
> > > > > > > > > What you guys exactly want to do? If you just want to pre-allocate
> > > > > > > > > coherent memory for latter usage,
> > > > > > > > 
> > > > > > > > Yes, just to preallocate not coherent, but rather contiguous memory for latter usage.
> > > > > > > > We use coherent memory because it turns out to be contiguous.
> > > > > > > 
> > > > > > > Hmm, you don't care about coherency? You just need contiguous memory?
> > > > > > 
> > > > > > Yes. We just need contiguous memory. Coherency is important as far as when dma
> > > > > > transfer finishes user land is able to see the new data. Could be done by something like
> > > > > > dma_{,un}map_single()
> > > > > 
> > > > > Then, we should avoid using coherent memory as I exaplained before. In
> > > > > addition, dma_alloc_coherent can't provide large enough contigous
> > > > > memory for some drivers so this patch doesn't help much.
> > > > 
> > > > Please, look at drivers/media/video/videobuf-dma-contig.c. Using coherent memory
> > > > is inavoidable for now, there is no alternative for it for now. The two new functions,
> > > > which I propose are just helpers for those of us who already use coherent memory
> > > > (via videobuf-dma-contig API). May be adding these two functions to 
> > > > drivers/media/video/videobuf-dma-contig.c will be better solution?
> > > 
> > > If you add something to the videobuf-dma-contig API, that's fine by me
> > > because drivers/media/video/videobuf-dma-contig.c uses the own
> > > structure and plays with dma_alloc_coherent. As long as a driver
> > > doesn't touch device->dma_mem directly, it's fine, I think (that is,
> > > dt3155v4l driver is broken). There are already some workarounds for
> > > contigous memory in several drivers anyway.
> > 
> > No, this will not work - this API has to be used from board code and 
> > videobuf can be built modular.
> > 
> > > We will have the proper API for contiguous memory. I don't think that
> > > adding such workaround to the DMA API is a good idea.
> > 
> > We have currently a number of boards broken in the mainline. They must be 
> > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > as I suggested earlier, we need either this or my patch series
> > 
> > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > 
> > for 2.6.36.
> 
> Why can't you revert a commit that causes the regression?
> 
> The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> responsible for the regression. And the patchset even exnteds the
> definition of the DMA API (dma_declare_coherent_memory). Such change
> shouldn't applied after rc1. I think that DMA-API.txt says that
> dma_declare_coherent_memory() handles coherent memory for a particular
> device. It's not for the API that reserves coherent memory that can be
> used for any device for a single device.
The patch that made the problem obvious for ARM is
309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
So this went in before v2.6.36-rc1.  One of the "architectures which
similar restrictions" is x86 BTW.

And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
addresses a hardware restriction.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Thu, 26 Aug 2010 11:53:11 +0200
Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:

> > > We have currently a number of boards broken in the mainline. They must be 
> > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > as I suggested earlier, we need either this or my patch series
> > > 
> > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > 
> > > for 2.6.36.
> > 
> > Why can't you revert a commit that causes the regression?
> > 
> > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > responsible for the regression. And the patchset even exnteds the
> > definition of the DMA API (dma_declare_coherent_memory). Such change
> > shouldn't applied after rc1. I think that DMA-API.txt says that
> > dma_declare_coherent_memory() handles coherent memory for a particular
> > device. It's not for the API that reserves coherent memory that can be
> > used for any device for a single device.
> The patch that made the problem obvious for ARM is
> 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> So this went in before v2.6.36-rc1.  One of the "architectures which
> similar restrictions" is x86 BTW.
> 
> And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> addresses a hardware restriction.

How these drivers were able to work without hitting the hardware restriction?

Re: [RFC][PATCH] add

[Russell King - ARM Linux]

On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> On Thu, 26 Aug 2010 11:53:11 +0200
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> 
> > > > We have currently a number of boards broken in the mainline. They must be 
> > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > as I suggested earlier, we need either this or my patch series
> > > > 
> > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > 
> > > > for 2.6.36.
> > > 
> > > Why can't you revert a commit that causes the regression?
> > > 
> > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > responsible for the regression. And the patchset even exnteds the
> > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > device. It's not for the API that reserves coherent memory that can be
> > > used for any device for a single device.
> > The patch that made the problem obvious for ARM is
> > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > So this went in before v2.6.36-rc1.  One of the "architectures which
> > similar restrictions" is x86 BTW.
> > 
> > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > addresses a hardware restriction.
> 
> How these drivers were able to work without hitting the hardware restriction?

Well, OMAP processors have experienced lock-ups due to multiple mappings of
memory, so the restriction in the architecture manual is for real.

But more the issue is that the behaviour you get from a region is _totally_
unpredictable (as the arch manual says).  With the VIPT caches, they can
be searched irrespective of whether the page tabkes indicate that it's
supposed to be cached or not - which means you can still hit cache lines
for an ioremap'd region.

And if you do, how do you know that the cached data is still valid - what
if it's some critical data that results in corruption - how do you know
whether that's happened or not?  It might not even cause a kernel
exception.

We have to adhere to the restrictions placed upon us by the architecture
at hand, and if that means device drivers break, so be it - at least we
get to know what needs to be fixed for these restrictions.

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Thu, 26 Aug 2010 18:54:40 +0100
Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > On Thu, 26 Aug 2010 11:53:11 +0200
> > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > 
> > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > as I suggested earlier, we need either this or my patch series
> > > > > 
> > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > 
> > > > > for 2.6.36.
> > > > 
> > > > Why can't you revert a commit that causes the regression?
> > > > 
> > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > responsible for the regression. And the patchset even exnteds the
> > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > device. It's not for the API that reserves coherent memory that can be
> > > > used for any device for a single device.
> > > The patch that made the problem obvious for ARM is
> > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > similar restrictions" is x86 BTW.
> > > 
> > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > addresses a hardware restriction.
> > 
> > How these drivers were able to work without hitting the hardware restriction?
> 
> Well, OMAP processors have experienced lock-ups due to multiple mappings of
> memory, so the restriction in the architecture manual is for real.
> 
> But more the issue is that the behaviour you get from a region is _totally_
> unpredictable (as the arch manual says).  With the VIPT caches, they can
> be searched irrespective of whether the page tabkes indicate that it's
> supposed to be cached or not - which means you can still hit cache lines
> for an ioremap'd region.
> 
> And if you do, how do you know that the cached data is still valid - what
> if it's some critical data that results in corruption - how do you know
> whether that's happened or not?  It might not even cause a kernel
> exception.
> 
> We have to adhere to the restrictions placed upon us by the architecture
> at hand, and if that means device drivers break, so be it - at least we
> get to know what needs to be fixed for these restrictions.

I didn't say the commit is technically wrong. I simply meant that the
commit broke some of working systems (so some complain, I guess).

As I wrote, the related DMA API wasn't changed in 2.6.36-rc1. It's not
related with the regression at all. As long as nobody tries to extend
the API wrongly after rc2, I have no complaint.

btw, Marin Mitov said that these drivers don't need coherent memory,
they just want contiguous memory. Telling the page allocater to
reserve some memory at boot time is enough, I guess.

Re: [RFC][PATCH] add

[@ 2010-08-27 4:41 UTC (permalink / raw)]

Hello,

On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> On Thu, 26 Aug 2010 11:53:11 +0200
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> 
> > > > We have currently a number of boards broken in the mainline. They must be 
> > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > as I suggested earlier, we need either this or my patch series
> > > > 
> > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > 
> > > > for 2.6.36.
> > > 
> > > Why can't you revert a commit that causes the regression?
> > > 
> > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > responsible for the regression. And the patchset even exnteds the
> > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > device. It's not for the API that reserves coherent memory that can be
> > > used for any device for a single device.
> > The patch that made the problem obvious for ARM is
> > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > So this went in before v2.6.36-rc1.  One of the "architectures which
> > similar restrictions" is x86 BTW.
> > 
> > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > addresses a hardware restriction.
> 
> How these drivers were able to work without hitting the hardware restriction?
In my case the machine in question is an ARMv5, the hardware restriction
is on ARMv6+ only.  You could argue that so the breaking patch for arm
should only break ARMv6, but I don't think this is sensible from a
maintainers POV.  We need an API that works independant of the machine
that runs the code.  And it's good to let developers that don't have the full
range of machines supported by the kernel at hand notice when they
introduce an incompatibility.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Fri, 27 Aug 2010 06:41:42 +0200
Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:

> Hello,
> 
> On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > On Thu, 26 Aug 2010 11:53:11 +0200
> > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > 
> > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > as I suggested earlier, we need either this or my patch series
> > > > > 
> > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > 
> > > > > for 2.6.36.
> > > > 
> > > > Why can't you revert a commit that causes the regression?
> > > > 
> > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > responsible for the regression. And the patchset even exnteds the
> > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > device. It's not for the API that reserves coherent memory that can be
> > > > used for any device for a single device.
> > > The patch that made the problem obvious for ARM is
> > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > similar restrictions" is x86 BTW.
> > > 
> > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > addresses a hardware restriction.
> > 
> > How these drivers were able to work without hitting the hardware restriction?
> In my case the machine in question is an ARMv5, the hardware restriction
> is on ARMv6+ only.  You could argue that so the breaking patch for arm
> should only break ARMv6, but I don't think this is sensible from a
> maintainers POV.  We need an API that works independant of the machine
> that runs the code.

Agreed. But insisting that the DMA API needs to be extended wrongly
after rc2 to fix the regression is not sensible too. The related DMA
API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
regression at all.

Re: [RFC][PATCH] add

[@ 2010-08-27 5:19 UTC (permalink / raw)]

Hey,

On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> On Fri, 27 Aug 2010 06:41:42 +0200
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > 
> > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > 
> > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > 
> > > > > > for 2.6.36.
> > > > > 
> > > > > Why can't you revert a commit that causes the regression?
> > > > > 
> > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > responsible for the regression. And the patchset even exnteds the
> > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > used for any device for a single device.
> > > > The patch that made the problem obvious for ARM is
> > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > similar restrictions" is x86 BTW.
> > > > 
> > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > addresses a hardware restriction.
> > > 
> > > How these drivers were able to work without hitting the hardware restriction?
> > In my case the machine in question is an ARMv5, the hardware restriction
> > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > should only break ARMv6, but I don't think this is sensible from a
> > maintainers POV.  We need an API that works independant of the machine
> > that runs the code.
> 
> Agreed. But insisting that the DMA API needs to be extended wrongly
> after rc2 to fix the regression is not sensible too. The related DMA
> API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> regression at all.
I think this isn't about "responsiblity".  Someone in arm-land found
that the way dma memory allocation worked for some time doesn't work
anymore on new generation chips.  As pointing out this problem was
expected to find some matches it was merged in the merge window.  One
such match is the current usage of the DMA API that doesn't currently
offer a way to do it right, so it needs a patch, no?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Fri, 27 Aug 2010 07:19:07 +0200
Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:

> Hey,
> 
> On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > On Fri, 27 Aug 2010 06:41:42 +0200
> > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > 
> > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > 
> > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > 
> > > > > > > for 2.6.36.
> > > > > > 
> > > > > > Why can't you revert a commit that causes the regression?
> > > > > > 
> > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > used for any device for a single device.
> > > > > The patch that made the problem obvious for ARM is
> > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > similar restrictions" is x86 BTW.
> > > > > 
> > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > addresses a hardware restriction.
> > > > 
> > > > How these drivers were able to work without hitting the hardware restriction?
> > > In my case the machine in question is an ARMv5, the hardware restriction
> > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > should only break ARMv6, but I don't think this is sensible from a
> > > maintainers POV.  We need an API that works independant of the machine
> > > that runs the code.
> > 
> > Agreed. But insisting that the DMA API needs to be extended wrongly
> > after rc2 to fix the regression is not sensible too. The related DMA
> > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > regression at all.
> I think this isn't about "responsiblity".  Someone in arm-land found
> that the way dma memory allocation worked for some time doesn't work
> anymore on new generation chips.  As pointing out this problem was
> expected to find some matches it was merged in the merge window.  One
> such match is the current usage of the DMA API that doesn't currently
> offer a way to do it right, so it needs a patch, no?

No, I don't think so. We are talking about a regression, right?

On new generation chips, something often doesn't work (which have
worked on old chips for some time). It's not a regresiion. I don't
think that it's sensible to make large change (especially after rc1)
to fix such issue. If you say that the DMA API doesn't work on new
chips and proposes a patch for the next merge window, it's sensible, I
suppose.

Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
API (and IMO in the wrong way). In addition, the patch might break the
current code. I really don't think that applying such patch after rc1
is senseble.

Re: [RFC][PATCH] add

[@ 2010-08-27 6:13 UTC (permalink / raw)]

Hello,

On Fri, Aug 27, 2010 at 02:57:59PM +0900, FUJITA Tomonori wrote:
> On Fri, 27 Aug 2010 07:19:07 +0200
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> 
> > Hey,
> > 
> > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > 
> > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > 
> > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > 
> > > > > > > > for 2.6.36.
> > > > > > > 
> > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > 
> > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > used for any device for a single device.
> > > > > > The patch that made the problem obvious for ARM is
> > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > similar restrictions" is x86 BTW.
> > > > > > 
> > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > addresses a hardware restriction.
> > > > > 
> > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > should only break ARMv6, but I don't think this is sensible from a
> > > > maintainers POV.  We need an API that works independant of the machine
> > > > that runs the code.
> > > 
> > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > after rc2 to fix the regression is not sensible too. The related DMA
> > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > regression at all.
> > I think this isn't about "responsiblity".  Someone in arm-land found
> > that the way dma memory allocation worked for some time doesn't work
> > anymore on new generation chips.  As pointing out this problem was
> > expected to find some matches it was merged in the merge window.  One
> > such match is the current usage of the DMA API that doesn't currently
> > offer a way to do it right, so it needs a patch, no?
> 
> No, I don't think so. We are talking about a regression, right?
> 
> On new generation chips, something often doesn't work (which have
> worked on old chips for some time). It's not a regresiion. I don't
> think that it's sensible to make large change (especially after rc1)
> to fix such issue. If you say that the DMA API doesn't work on new
> chips and proposes a patch for the next merge window, it's sensible, I
> suppose.
> 
> Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> API (and IMO in the wrong way). In addition, the patch might break the
> current code. I really don't think that applying such patch after rc1
> is senseble.
So you suggest to revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 or at
least restrict it to ARMv6+ and fix the problem during the next merge
window?  Russell?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Marin Mitov]

On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> On Fri, 27 Aug 2010 07:19:07 +0200
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> 
> > Hey,
> > 
> > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > 
> > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > 
> > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > 
> > > > > > > > for 2.6.36.
> > > > > > > 
> > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > 
> > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > used for any device for a single device.
> > > > > > The patch that made the problem obvious for ARM is
> > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > similar restrictions" is x86 BTW.
> > > > > > 
> > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > addresses a hardware restriction.
> > > > > 
> > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > should only break ARMv6, but I don't think this is sensible from a
> > > > maintainers POV.  We need an API that works independant of the machine
> > > > that runs the code.
> > > 
> > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > after rc2 to fix the regression is not sensible too. The related DMA
> > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > regression at all.
> > I think this isn't about "responsiblity".  Someone in arm-land found
> > that the way dma memory allocation worked for some time doesn't work
> > anymore on new generation chips.  As pointing out this problem was
> > expected to find some matches it was merged in the merge window.  One
> > such match is the current usage of the DMA API that doesn't currently
> > offer a way to do it right, so it needs a patch, no?
> 
> No, I don't think so. We are talking about a regression, right?
> 
> On new generation chips, something often doesn't work (which have
> worked on old chips for some time). It's not a regresiion. I don't
> think that it's sensible to make large change (especially after rc1)
> to fix such issue. If you say that the DMA API doesn't work on new
> chips and proposes a patch for the next merge window, it's sensible, I
> suppose.
> 
> Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> API (and IMO in the wrong way). 
> In addition, the patch might break the
> current code. 

To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
"extend the DMA API", so if you do not use the new API (and no current code is using it)
you cannot "break the current code". 

Thanks,

Marin Mitov

> I really don't think that applying such patch after rc1
> is senseble.
> 

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Fri, 27 Aug 2010 09:23:21 +0300
Marin Mitov <mitov@issp.bas.bg> wrote:

> On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> > On Fri, 27 Aug 2010 07:19:07 +0200
> > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > 
> > > Hey,
> > > 
> > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > 
> > > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > > 
> > > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > > 
> > > > > > > > > for 2.6.36.
> > > > > > > > 
> > > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > > 
> > > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > > used for any device for a single device.
> > > > > > > The patch that made the problem obvious for ARM is
> > > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > > similar restrictions" is x86 BTW.
> > > > > > > 
> > > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > > addresses a hardware restriction.
> > > > > > 
> > > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > > should only break ARMv6, but I don't think this is sensible from a
> > > > > maintainers POV.  We need an API that works independant of the machine
> > > > > that runs the code.
> > > > 
> > > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > > after rc2 to fix the regression is not sensible too. The related DMA
> > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > > regression at all.
> > > I think this isn't about "responsiblity".  Someone in arm-land found
> > > that the way dma memory allocation worked for some time doesn't work
> > > anymore on new generation chips.  As pointing out this problem was
> > > expected to find some matches it was merged in the merge window.  One
> > > such match is the current usage of the DMA API that doesn't currently
> > > offer a way to do it right, so it needs a patch, no?
> > 
> > No, I don't think so. We are talking about a regression, right?
> > 
> > On new generation chips, something often doesn't work (which have
> > worked on old chips for some time). It's not a regresiion. I don't
> > think that it's sensible to make large change (especially after rc1)
> > to fix such issue. If you say that the DMA API doesn't work on new
> > chips and proposes a patch for the next merge window, it's sensible, I
> > suppose.
> > 
> > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> > API (and IMO in the wrong way). 
> > In addition, the patch might break the
> > current code. 
> 
> To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
> "extend the DMA API", so if you do not use the new API (and no current code is using it)
> you cannot "break the current code". 

Looks like that the patch adds the new API that touches the exisitng
code. It means the existing code could break. So the exsising API
could break too.

http://thread.gmane.org/gmane.linux.ports.sh.devel/8595

Re: [RFC][PATCH] add

[@ 2010-08-27 6:38 UTC (permalink / raw)]

Hello,

On Fri, Aug 27, 2010 at 03:32:14PM +0900, FUJITA Tomonori wrote:
> On Fri, 27 Aug 2010 09:23:21 +0300
> Marin Mitov <mitov@issp.bas.bg> wrote:
> 
> > On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> > > On Fri, 27 Aug 2010 07:19:07 +0200
> > > Uwe Kleine-K^[$(D+S^[(Bnig <u.kleine-koenig@pengutronix.de> wrote:
> > > 
> > > > Hey,
> > > > 
> > > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > > > Uwe Kleine-K^[$(D+S^[(Bnig <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > > > Uwe Kleine-K^[$(D+S^[(Bnig <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > 
> > > > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > > > 
> > > > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > > > 
> > > > > > > > > > for 2.6.36.
> > > > > > > > > 
> > > > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > > > 
> > > > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > > > used for any device for a single device.
> > > > > > > > The patch that made the problem obvious for ARM is
> > > > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > > > similar restrictions" is x86 BTW.
> > > > > > > > 
> > > > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > > > addresses a hardware restriction.
> > > > > > > 
> > > > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > > > should only break ARMv6, but I don't think this is sensible from a
> > > > > > maintainers POV.  We need an API that works independant of the machine
> > > > > > that runs the code.
> > > > > 
> > > > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > > > after rc2 to fix the regression is not sensible too. The related DMA
> > > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > > > regression at all.
> > > > I think this isn't about "responsiblity".  Someone in arm-land found
> > > > that the way dma memory allocation worked for some time doesn't work
> > > > anymore on new generation chips.  As pointing out this problem was
> > > > expected to find some matches it was merged in the merge window.  One
> > > > such match is the current usage of the DMA API that doesn't currently
> > > > offer a way to do it right, so it needs a patch, no?
> > > 
> > > No, I don't think so. We are talking about a regression, right?
> > > 
> > > On new generation chips, something often doesn't work (which have
> > > worked on old chips for some time). It's not a regresiion. I don't
> > > think that it's sensible to make large change (especially after rc1)
> > > to fix such issue. If you say that the DMA API doesn't work on new
> > > chips and proposes a patch for the next merge window, it's sensible, I
> > > suppose.
> > > 
> > > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> > > API (and IMO in the wrong way). 
> > > In addition, the patch might break the
> > > current code. 
> > 
> > To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
> > "extend the DMA API", so if you do not use the new API (and no current code is using it)
> > you cannot "break the current code". 
> 
> Looks like that the patch adds the new API that touches the exisitng
> code. It means the existing code could break. So the exsising API
> could break too.
> 
> http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
I'm still trying to find out what you actually suggest we should do now.
Maybe this is a request for a minimal "fix" without the cleanups
Guennadi did?  That is only patches 2(?), 4 and 5 of the series?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Marin Mitov]

On Friday, August 27, 2010 09:32:14 am FUJITA Tomonori wrote:
> On Fri, 27 Aug 2010 09:23:21 +0300
> Marin Mitov <mitov@issp.bas.bg> wrote:
> 
> > On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> > > On Fri, 27 Aug 2010 07:19:07 +0200
> > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > 
> > > > Hey,
> > > > 
> > > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > 
> > > > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > > > 
> > > > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > > > 
> > > > > > > > > > for 2.6.36.
> > > > > > > > > 
> > > > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > > > 
> > > > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > > > used for any device for a single device.
> > > > > > > > The patch that made the problem obvious for ARM is
> > > > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > > > similar restrictions" is x86 BTW.
> > > > > > > > 
> > > > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > > > addresses a hardware restriction.
> > > > > > > 
> > > > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > > > should only break ARMv6, but I don't think this is sensible from a
> > > > > > maintainers POV.  We need an API that works independant of the machine
> > > > > > that runs the code.
> > > > > 
> > > > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > > > after rc2 to fix the regression is not sensible too. The related DMA
> > > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > > > regression at all.
> > > > I think this isn't about "responsiblity".  Someone in arm-land found
> > > > that the way dma memory allocation worked for some time doesn't work
> > > > anymore on new generation chips.  As pointing out this problem was
> > > > expected to find some matches it was merged in the merge window.  One
> > > > such match is the current usage of the DMA API that doesn't currently
> > > > offer a way to do it right, so it needs a patch, no?
> > > 
> > > No, I don't think so. We are talking about a regression, right?
> > > 
> > > On new generation chips, something often doesn't work (which have
> > > worked on old chips for some time). It's not a regresiion. I don't
> > > think that it's sensible to make large change (especially after rc1)
> > > to fix such issue. If you say that the DMA API doesn't work on new
> > > chips and proposes a patch for the next merge window, it's sensible, I
> > > suppose.
> > > 
> > > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> > > API (and IMO in the wrong way). 
> > > In addition, the patch might break the
> > > current code. 
> > 
> > To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
> > "extend the DMA API", so if you do not use the new API (and no current code is using it)
> > you cannot "break the current code". 
> 
> Looks like that the patch adds the new API that touches the exisitng
> code. It means the existing code could break. So the exsising API
> could break too.
> 
> http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Marin Mitov]

On Friday, August 27, 2010 09:32:14 am FUJITA Tomonori wrote:
> On Fri, 27 Aug 2010 09:23:21 +0300
> Marin Mitov <mitov@issp.bas.bg> wrote:
> 
> > On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> > > On Fri, 27 Aug 2010 07:19:07 +0200
> > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > 
> > > > Hey,
> > > > 
> > > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > 
> > > > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > > > 
> > > > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > > > 
> > > > > > > > > > for 2.6.36.
> > > > > > > > > 
> > > > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > > > 
> > > > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > > > used for any device for a single device.
> > > > > > > > The patch that made the problem obvious for ARM is
> > > > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > > > similar restrictions" is x86 BTW.
> > > > > > > > 
> > > > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > > > addresses a hardware restriction.
> > > > > > > 
> > > > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > > > should only break ARMv6, but I don't think this is sensible from a
> > > > > > maintainers POV.  We need an API that works independant of the machine
> > > > > > that runs the code.
> > > > > 
> > > > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > > > after rc2 to fix the regression is not sensible too. The related DMA
> > > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > > > regression at all.
> > > > I think this isn't about "responsiblity".  Someone in arm-land found
> > > > that the way dma memory allocation worked for some time doesn't work
> > > > anymore on new generation chips.  As pointing out this problem was
> > > > expected to find some matches it was merged in the merge window.  One
> > > > such match is the current usage of the DMA API that doesn't currently
> > > > offer a way to do it right, so it needs a patch, no?
> > > 
> > > No, I don't think so. We are talking about a regression, right?
> > > 
> > > On new generation chips, something often doesn't work (which have
> > > worked on old chips for some time). It's not a regresiion. I don't
> > > think that it's sensible to make large change (especially after rc1)
> > > to fix such issue. If you say that the DMA API doesn't work on new
> > > chips and proposes a patch for the next merge window, it's sensible, I
> > > suppose.
> > > 
> > > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> > > API (and IMO in the wrong way). 
> > > In addition, the patch might break the
> > > current code. 
> > 
> > To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
> > "extend the DMA API", so if you do not use the new API (and no current code is using it)
> > you cannot "break the current code". 
> 
> Looks like that the patch adds the new API that touches the exisitng
> code. It means the existing code could break. So the exsising API
> could break too.
> 
> http://thread.gmane.org/gmane.linux.ports.sh.devel/8595

The above reference is not my patch. I am speaking for my patch:

http://lkml.org/lkml/2010/8/19/200

The only point my patch touches the existing code is struct device's member dma_mem
and that is in condition you __use__ the new API, so you could decide yourself if it 
could break the current code. As far as one does not use the new API - nothing is touched,
nothing can break. If one uses the new API, only the user can suffer if the new API have
bugs.

Thanks,

Marin Mitov

Re: [RFC][PATCH] add

[FUJITA Tomonori]

On Sat, 28 Aug 2010 09:14:25 +0300
Marin Mitov <mitov@issp.bas.bg> wrote:

> On Friday, August 27, 2010 09:32:14 am FUJITA Tomonori wrote:
> > On Fri, 27 Aug 2010 09:23:21 +0300
> > Marin Mitov <mitov@issp.bas.bg> wrote:
> > 
> > > On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> > > > On Fri, 27 Aug 2010 07:19:07 +0200
> > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > 
> > > > > Hey,
> > > > > 
> > > > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > > > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > > 
> > > > > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > > > > 
> > > > > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > > > > 
> > > > > > > > > > > for 2.6.36.
> > > > > > > > > > 
> > > > > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > > > > 
> > > > > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > > > > used for any device for a single device.
> > > > > > > > > The patch that made the problem obvious for ARM is
> > > > > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > > > > similar restrictions" is x86 BTW.
> > > > > > > > > 
> > > > > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > > > > addresses a hardware restriction.
> > > > > > > > 
> > > > > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > > > > should only break ARMv6, but I don't think this is sensible from a
> > > > > > > maintainers POV.  We need an API that works independant of the machine
> > > > > > > that runs the code.
> > > > > > 
> > > > > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > > > > after rc2 to fix the regression is not sensible too. The related DMA
> > > > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > > > > regression at all.
> > > > > I think this isn't about "responsiblity".  Someone in arm-land found
> > > > > that the way dma memory allocation worked for some time doesn't work
> > > > > anymore on new generation chips.  As pointing out this problem was
> > > > > expected to find some matches it was merged in the merge window.  One
> > > > > such match is the current usage of the DMA API that doesn't currently
> > > > > offer a way to do it right, so it needs a patch, no?
> > > > 
> > > > No, I don't think so. We are talking about a regression, right?
> > > > 
> > > > On new generation chips, something often doesn't work (which have
> > > > worked on old chips for some time). It's not a regresiion. I don't
> > > > think that it's sensible to make large change (especially after rc1)
> > > > to fix such issue. If you say that the DMA API doesn't work on new
> > > > chips and proposes a patch for the next merge window, it's sensible, I
> > > > suppose.
> > > > 
> > > > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> > > > API (and IMO in the wrong way). 
> > > > In addition, the patch might break the
> > > > current code. 
> > > 
> > > To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
> > > "extend the DMA API", so if you do not use the new API (and no current code is using it)
> > > you cannot "break the current code". 
> > 
> > Looks like that the patch adds the new API that touches the exisitng
> > code. It means the existing code could break. So the exsising API
> > could break too.
> > 
> > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> 
> The above reference is not my patch. I am speaking for my patch:
> 
> http://lkml.org/lkml/2010/8/19/200

I think that I already NACK'ed the patch.

1) drivers/media/videobuf-dma-contig.c should not use
dma_alloc_coherent. We shouldn't support the proposed API.

2) I don't think that the DMA API (drivers/base/dma-mapping.c) is not
for creating "cache". Generally, the kernel uses "pool" concept for
something like that.

IMHO, reverting the commit 309caa9cc6ff39d261264ec4ff10e29489afc8f8
temporary (or temporary disabling it for systems that had worked) is
the most reasonable approach. I don't think that breaking systems that
had worked is a good idea even if the patch does the right thing. I
believe that we need to fix the broken solution
(videobuf-dma-contig.c) before the commit.

Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Marin Mitov]

On Saturday, August 28, 2010 10:10:28 am FUJITA Tomonori wrote:
> On Sat, 28 Aug 2010 09:14:25 +0300
> Marin Mitov <mitov@issp.bas.bg> wrote:
> 
> > On Friday, August 27, 2010 09:32:14 am FUJITA Tomonori wrote:
> > > On Fri, 27 Aug 2010 09:23:21 +0300
> > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > 
> > > > On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote:
> > > > > On Fri, 27 Aug 2010 07:19:07 +0200
> > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > 
> > > > > > Hey,
> > > > > > 
> > > > > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote:
> > > > > > > On Fri, 27 Aug 2010 06:41:42 +0200
> > > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote:
> > > > > > > > > On Thu, 26 Aug 2010 11:53:11 +0200
> > > > > > > > > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> > > > > > > > > 
> > > > > > > > > > > > We have currently a number of boards broken in the mainline. They must be 
> > > > > > > > > > > > fixed for 2.6.36. I don't think the mentioned API will do this for us. So, 
> > > > > > > > > > > > as I suggested earlier, we need either this or my patch series
> > > > > > > > > > > > 
> > > > > > > > > > > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > > > > > > > > > > > 
> > > > > > > > > > > > for 2.6.36.
> > > > > > > > > > > 
> > > > > > > > > > > Why can't you revert a commit that causes the regression?
> > > > > > > > > > > 
> > > > > > > > > > > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not
> > > > > > > > > > > responsible for the regression. And the patchset even exnteds the
> > > > > > > > > > > definition of the DMA API (dma_declare_coherent_memory). Such change
> > > > > > > > > > > shouldn't applied after rc1. I think that DMA-API.txt says that
> > > > > > > > > > > dma_declare_coherent_memory() handles coherent memory for a particular
> > > > > > > > > > > device. It's not for the API that reserves coherent memory that can be
> > > > > > > > > > > used for any device for a single device.
> > > > > > > > > > The patch that made the problem obvious for ARM is
> > > > > > > > > > 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12.
> > > > > > > > > > So this went in before v2.6.36-rc1.  One of the "architectures which
> > > > > > > > > > similar restrictions" is x86 BTW.
> > > > > > > > > > 
> > > > > > > > > > And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it
> > > > > > > > > > addresses a hardware restriction.
> > > > > > > > > 
> > > > > > > > > How these drivers were able to work without hitting the hardware restriction?
> > > > > > > > In my case the machine in question is an ARMv5, the hardware restriction
> > > > > > > > is on ARMv6+ only.  You could argue that so the breaking patch for arm
> > > > > > > > should only break ARMv6, but I don't think this is sensible from a
> > > > > > > > maintainers POV.  We need an API that works independant of the machine
> > > > > > > > that runs the code.
> > > > > > > 
> > > > > > > Agreed. But insisting that the DMA API needs to be extended wrongly
> > > > > > > after rc2 to fix the regression is not sensible too. The related DMA
> > > > > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the
> > > > > > > regression at all.
> > > > > > I think this isn't about "responsiblity".  Someone in arm-land found
> > > > > > that the way dma memory allocation worked for some time doesn't work
> > > > > > anymore on new generation chips.  As pointing out this problem was
> > > > > > expected to find some matches it was merged in the merge window.  One
> > > > > > such match is the current usage of the DMA API that doesn't currently
> > > > > > offer a way to do it right, so it needs a patch, no?
> > > > > 
> > > > > No, I don't think so. We are talking about a regression, right?
> > > > > 
> > > > > On new generation chips, something often doesn't work (which have
> > > > > worked on old chips for some time). It's not a regresiion. I don't
> > > > > think that it's sensible to make large change (especially after rc1)
> > > > > to fix such issue. If you say that the DMA API doesn't work on new
> > > > > chips and proposes a patch for the next merge window, it's sensible, I
> > > > > suppose.
> > > > > 
> > > > > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA
> > > > > API (and IMO in the wrong way). 
> > > > > In addition, the patch might break the
> > > > > current code. 
> > > > 
> > > > To "break the current code" is simply not possible. Sorry to oppose. As you have written it 
> > > > "extend the DMA API", so if you do not use the new API (and no current code is using it)
> > > > you cannot "break the current code". 
> > > 
> > > Looks like that the patch adds the new API that touches the exisitng
> > > code. It means the existing code could break. So the exsising API
> > > could break too.
> > > 
> > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595
> > 
> > The above reference is not my patch. I am speaking for my patch:
> > 
> > http://lkml.org/lkml/2010/8/19/200
> 
> I think that I already NACK'ed the patch.

OK.

Thanks,

Marin Mitov

> 
> 1) drivers/media/videobuf-dma-contig.c should not use
> dma_alloc_coherent. We shouldn't support the proposed API.
> 
> 2) I don't think that the DMA API (drivers/base/dma-mapping.c) is not
> for creating "cache". Generally, the kernel uses "pool" concept for
> something like that.
> 
> IMHO, reverting the commit 309caa9cc6ff39d261264ec4ff10e29489afc8f8
> temporary (or temporary disabling it for systems that had worked) is
> the most reasonable approach. I don't think that breaking systems that
> had worked is a good idea even if the patch does the right thing. I
> believe that we need to fix the broken solution
> (videobuf-dma-contig.c) before the commit.
> --
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