[PATCH 0/3] arm64: dts: r8a7796: Add CAN/CAN FD support

[Simon Horman]

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
> > Hi Chris,
> > 
> > On Thu, Nov 24, 2016 at 10:05:08AM +0000, Chris Paterson wrote:
> > > Hello Simon,
> > >
> > > From: Simon Horman [mailto:horms at verge.net.au]
> > > 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.