Hi Chris, On Thu, Nov 24, 2016 at 02:25:06PM +0000, Chris Paterson wrote: > Hello Simon, > > From: Simon Horman [mailto:horms@xxxxxxxxxxxx] > 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@xxxxxxxxxxxx] > > > 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: ... > > > > 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. Thanks for the explanation. I think it would be good to proceed with a v2. -- 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
