Re: CoreSight framework and drivers

[Pratik Patel <pratikp@codeaurora.org>]

On Thu, Dec 20, 2012 at 11:40:11PM +0000, Russell King - ARM Linux wrote:
> On Thu, Dec 20, 2012 at 04:54:38PM -0600, Jon Hunter wrote:
> > On 12/20/2012 01:51 PM, Pratik Patel wrote:
> > > Ok, so are you referring to making CoreSight devices register
> > > with AMBA bus instead of platform bus keeping everything else
> > > intact?
> > 
> > Yes exactly. However, please note I am not saying that we should do
> > this, and I asking what direction does the community want us to take
> > here? Platform bus or AMBA bus?
> 
> One of the issues which worries me about mixing peripheral drivers on
> random different buses is... what happens when we end up with a SoC
> which gates the APB clock at bus level (there are SoCs which gate the
> APB clock at peripheral level.)  In other words, an APB bus only gets
> clocked upon request.
> 
> We can deal with that with the infrastructure we have in place in the
> AMBA bus layer, but not with the platform bus - we'd have to teach the
> platform bus driver about the special APB clock instead of having it
> handled primerily at the bus layer.
> 
> At least the coresight ETM peripherals make use of the APB bus.  They
> have a whole pile of registers on the APB bus, and they have the
> primecell IDs stored in the last words of the peripheral, again just
> like the other primecell devices we have using the AMBA bus layer.
> 
> What I'd say is... why stick it on a different bus type from the other
> peripherals which might make things harder in the future?

Thanks for the info. I will look into using the AMBA bus instead
of the platform bus but one issue I notice is that AMBA framework
seems to support one contiguous register space.

CoreSight STM typically has a config register space and a
stimulus port/channel register space and these can be
non-contiguous in the chip memory map.

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