[PATCH 0/3] arm64: dts: r8a7796: Add CAN/CAN FD support

[Chris Paterson]

Hello Simon,

From: Simon Horman [mailto:horms at verge.net.au]
Sent: 24 November 2016 10:18
> Hi Chris,
> 
> On Thu, Nov 24, 2016 at 10:05:08AM +0000, Chris Paterson wrote:
> > Hello Simon,
> >
> > From: Simon Horman [mailto:horms at verge.net.au]
> > Sent: 23 November 2016 14:30
> > > On Wed, Nov 23, 2016 at 02:18:13PM +0100, Marc Kleine-Budde wrote:
> > > > On 11/23/2016 01:14 PM, Chris Paterson wrote:
> > > > > This patch series adds CAN and CAN FD support to the r8a7796.
> > > > >
> > > > > Based on renesas-devel-20161122-v4.9-rc6.
> > > > >
> > > > > Chris Paterson (3):
> > > > >   arm64: dts: r8a7796: Add CAN external clock support
> > > > >   arm64: dts: r8a7796: Add CAN support
> > > > >   arm64: dts: r8a7796: Add CAN FD support
> > > > >
> > > > >  .../devicetree/bindings/net/can/rcar_can.txt       | 12 +++--
> > > > >  .../devicetree/bindings/net/can/rcar_canfd.txt     | 12 +++--
> > > > >  arch/arm64/boot/dts/renesas/r8a7796.dtsi           | 61
> > > ++++++++++++++++++++++
> > > > >  3 files changed, 75 insertions(+), 10 deletions(-)
> > > >
> > > > For all three:
> > > >
> > > > Acked-by: Marc Kleine-Budde <mkl at pengutronix.de>
> > > >
> > > > Who takes this series?
> > >
> > > I would like to see these patches split up so that the
> > > .../devicetree/bindings/ portions can go through you whole the
> > > arch/arm64/boot/dts/renesas/ portions go thorugh my renesas tree.
> >
> > Okay, will do.
> 
> Thanks.
> 
> > > Regarding the arch/arm64/boot/dts/renesas/ portion, I would like
> > > some consideration given to what effect enabling memory above 4Gb
> > > (64bit
> > > addressing) would have.
> >
> > Can you give me some guidance here? I'm not sure what you're referring
> > to. As far as I know the DT reg definition here is 64-bit, or are you
> > referring to DMA usage? If the later, neither CAN driver uses DMA.
> 
> Sorry for not being clearer.
> 
> What I would like to know is if there are any problems in the CAN driver or
> hardware that would prevent it from functioning with memory that requires
> 64bit addressing present.
> 
> If the CAN hardware cannot use DMA then DMA doesn't need to be taken
> into account. But if it DMA could be enabled in future for CAN, for example
> after some driver enhancements, then it would be good to know if 64bit
> memory can be supported - if not it would imply DMA cannot be enabled.

Thank you for the clarification.

The CAN interface for r8a7795/6 does not support DMA.

With CAN FD there is currently a H/W issue that means DMA is unusable. Potentially this issue could be fixed in the future and DMA support could be added to the driver. If this happens I can see no reason why the CAN FD IP wouldn't be able to handle DMA transfers when using 64bit addressing.

> 
> As for non-DMA mode, will this function if memory above 4G is present?
> If not then in theory such memory couldn't be enabled if the CAN driver is
> enabled. This is my main concern.

Yes, it functions fine. We have already tested this with the Renesas v3.3.2 BSP with >4Gb memory.

If this is explanation okay for you, I'll proceed with a v2 splitting off the DT bindings documentation.

Kind regards, Chris

> 
> Does the above help?