[RFC,0/5] ARM: Raspberry Pi 4 DMA support

Message

Nicolas Saenz Julienne Oct. 14, 2019, 6:31 p.m. UTC

Hi all,
the Raspberry Pi 4 offers up to 4GB of memory, of which only the first
is DMA capable device wide. This forces us to use of bounce buffers,
which are currently not very well supported by ARM's custom DMA ops.
Among other things the current mechanism (see dmabounce.c) isn't
suitable for high memory. Instead of fixing it, this series introduces a
way of selecting dma-direct as the default DMA ops provider which allows
for the Raspberry Pi to make use of swiotlb.

Regards,
Nicolas

---

Nicolas Saenz Julienne (5):
  dma/direct: turn ARCH_ZONE_DMA_BITS into a variable
  ARM: introduce arm_dma_direct
  ARM: let machines select dma-direct over arch's DMA implementation
  dma/direct: check for overflows in ARM's dma_capable()
  ARM: bcm2711: use dma-direct

 arch/arm/include/asm/dma-direct.h  |  6 ++++++
 arch/arm/include/asm/dma-mapping.h |  3 ++-
 arch/arm/include/asm/dma.h         |  2 ++
 arch/arm/include/asm/mach/arch.h   |  1 +
 arch/arm/mach-bcm/Kconfig          |  1 +
 arch/arm/mach-bcm/bcm2711.c        |  1 +
 arch/arm/mm/dma-mapping.c          | 10 ++--------
 arch/arm/mm/init.c                 | 21 ++++++++++++++++++++-
 arch/arm64/include/asm/page.h      |  2 --
 arch/arm64/mm/init.c               |  9 +++++++--
 arch/powerpc/include/asm/page.h    |  9 ---------
 arch/powerpc/mm/mem.c              | 20 +++++++++++++++-----
 arch/s390/include/asm/page.h       |  2 --
 arch/s390/mm/init.c                |  1 +
 include/linux/dma-direct.h         |  2 ++
 kernel/dma/direct.c                | 13 ++++++-------
 16 files changed, 66 insertions(+), 37 deletions(-)

Comments

Catalin Marinas Oct. 14, 2019, 8:59 p.m. UTC | #1

On Mon, Oct 14, 2019 at 08:31:02PM +0200, Nicolas Saenz Julienne wrote:
> the Raspberry Pi 4 offers up to 4GB of memory, of which only the first
> is DMA capable device wide. This forces us to use of bounce buffers,
> which are currently not very well supported by ARM's custom DMA ops.
> Among other things the current mechanism (see dmabounce.c) isn't
> suitable for high memory. Instead of fixing it, this series introduces a
> way of selecting dma-direct as the default DMA ops provider which allows
> for the Raspberry Pi to make use of swiotlb.

I presume these patches go on top of this series:

http://lkml.kernel.org/r/[e-mail]

which I queued here:

https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/zone-dma

Nicolas Saenz Julienne Oct. 15, 2019, 7:48 a.m. UTC | #2

On Mon, 2019-10-14 at 21:59 +0100, Catalin Marinas wrote:
> On Mon, Oct 14, 2019 at 08:31:02PM +0200, Nicolas Saenz Julienne wrote:
> > the Raspberry Pi 4 offers up to 4GB of memory, of which only the first
> > is DMA capable device wide. This forces us to use of bounce buffers,
> > which are currently not very well supported by ARM's custom DMA ops.
> > Among other things the current mechanism (see dmabounce.c) isn't
> > suitable for high memory. Instead of fixing it, this series introduces a
> > way of selecting dma-direct as the default DMA ops provider which allows
> > for the Raspberry Pi to make use of swiotlb.
> 
> I presume these patches go on top of this series:
> 
> http://lkml.kernel.org/r/[e-mail]

Yes, forgot to mention it. It's relevant for the first patch.

> 
> which I queued here:
> 
> 
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/zone-dma

Thanks!

A little off topic but I was wondering if you have a preferred way to refer to
the arm architecture in a way that it unambiguously excludes arm64 (for example
arm32 would work).

Regards,
Nicolas

Catalin Marinas Oct. 15, 2019, 5:46 p.m. UTC | #3

On Tue, Oct 15, 2019 at 09:48:22AM +0200, Nicolas Saenz Julienne wrote:
> A little off topic but I was wondering if you have a preferred way to refer to
> the arm architecture in a way that it unambiguously excludes arm64 (for example
> arm32 would work).

arm32 should be fine. Neither arm64 nor arm32 are officially endorsed
ARM Ltd names (officially the exception model is AArch32 while the
instruction set is one of A32/T32/T16).