Hi Chris,

On Thu, Nov 24, 2016 at 3:25 PM, Chris Paterson
[off-list ref] wrote:

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

quoted

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

quoted

From: Simon Horman [mailto:horms at verge.net.au]

quoted

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.

Is that issue present on R-Car M3-W, or only on R-Car H3 ES1.x?

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.

Yep, AFAIK it uses SYS-DMAC, which supports 64-bit addressing.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds