Hi Chris,

On Thu, Nov 24, 2016 at 02:25:06PM +0000, Chris Paterson wrote:

Hello Simon,

From: Simon Horman [mailto:horms at verge.net.au]
Sent: 24 November 2016 10:18

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Hi Chris,

On Thu, Nov 24, 2016 at 10:05:08AM +0000, Chris Paterson wrote:

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Hello Simon,

From: Simon Horman [mailto:horms at verge.net.au]
Sent: 23 November 2016 14:30

quoted

On Wed, Nov 23, 2016 at 02:18:13PM +0100, Marc Kleine-Budde wrote:

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On 11/23/2016 01:14 PM, Chris Paterson wrote:

...

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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.

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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.

Thanks for the explanation. I think it would be good to proceed with a v2.