Hi Chris, On Thu, Nov 24, 2016 at 3:25 PM, Chris Paterson <Chris.Paterson2@xxxxxxxxxxx> wrote: > From: Simon Horman [mailto:horms@xxxxxxxxxxxx] > Sent: 24 November 2016 10:18 >> On Thu, Nov 24, 2016 at 10:05:08AM +0000, Chris Paterson wrote: >> > From: Simon Horman [mailto:horms@xxxxxxxxxxxx] >> > > 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@xxxxxxxxxxxxxx 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 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
