Hello Geert, From: geert.uytterhoeven@xxxxxxxxx Sent: 24 November 2016 16:42 > 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? Both > > > 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. Yep > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@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 ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
