linux-kernel - Re: CoreSight framework and drivers

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Date:	Thu, 20 Dec 2012 16:54:38 -0600
From:	Jon Hunter <jon-hunter@...com>
To:	Pratik Patel <pratikp@...eaurora.org>
CC:	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	<linux-arm-msm@...r.kernel.org>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	Will Deacon <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>,
	"magnus.p.persson@...ricsson.com" <magnus.p.persson@...ricsson.com>,
	"david.rusling@...aro.org" <david.rusling@...aro.org>,
	"arve@...roid.com" <arve@...roid.com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"d-deao@...com" <d-deao@...com>,
	"christian.bejram@...ricsson.com" <christian.bejram@...ricsson.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: CoreSight framework and drivers


On 12/20/2012 01:51 PM, Pratik Patel wrote:
> On Thu, Dec 20, 2012 at 11:46:13AM -0600, Jon Hunter wrote:
>>
>> On 12/19/2012 03:24 PM, Pratik Patel wrote:
>>
>> [snip]
>>
>>> Currently we use the CoreSight virtual bus to conveniently list
>>> sysfs configuration attributes for all the registered CoreSight
>>> devices.
>>>
>>> For eg:
>>> /sys/bus/coresight/devices/coresight-etm0/<attribute>
>>> /sys/bus/coresight/devices/coresight-etm1/<attribute>
>>> /sys/bus/coresight/devices/coresight-stm/<attribute>
>>> /sys/bus/coresight/devices/coresight-tmc-etf/<attribute>
>>> ...
>>> ...
>>>
>>> Some of the attributes are based on device type (i.e. source,
>>> link or sink) so they will exist for all devices of that type
>>> while some are device specific.
>>>
>>> Maybe I am misunderstanding the question but are you suggesting
>>> to register CoreSight devices to the AMBA bus instead of the
>>> CoreSight core layer code?
>>
>> Yes exactly.
>>
>>> Will Deacon mentioned earlier that AMBA framework can be changed
>>> to accomodate devices with a different class but I am more
>>> concerned with losing some of the stuff that the core layer code
>>> does (eg. coresight_register, coresight_enable, coresight_disable
>>> in coresight.c) if we register CoreSight drivers to the AMBA bus
>>> without letting the core layer know about the device connections.
>>
>> I may be missing something, but couldn't you keep all the
>> register/enable/disable stuff but just register the device with the amba
>> bus? Obviously some changes would need to be made.
>>
> 
> 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?

>> Personally, I don't have strong feeling either way, but we have ETM/ETB
>> drivers using AMBA today and so I am hoping we can come to agreement on
>> this going forward.
>>
>> Russell, Will, what are your thoughts?
>>
>> Otherwise, looking at the code, I like what you have implemented. I
>> still need to look closer, but I am struggling to figure out how a
>> coresight device such as the cross-trigger-interface fits with this
>> model. This model appears to be geared towards coresight devices used
>> for traces purposes and are either source, links or sinks. The
>> cross-trigger-interface is not a source or a sink. However, although you
>> it could be considered as a link (routing events), it is not really, as
>> it may not link to other coresight sinks/source.
>>
>> In my case, I have PMU-IRQ --> CTI --> GIC. So a non-coresight source
>> and sink. In away the CTI looks more like a 2nd-level interrupt
>> controller than anything else. Hence, another type of coresight device
>> may be needed in addition to source, links and sinks. Or link is
>> extended in some way to connect to non-coresight sources/sinks.
>>
>> Let me know if you have any thoughts.
>>
> 
> I had left the "None" type for miscellaneous stuff but I agree it
> should be a separate type - maybe "debug".
> 
> Having said that I like the CTI driver you have uploaded. Need to
> look at it in more detail. Since CTI connections can vary between
> chip to chip, we need a generic way to deal with it.

Yes if you have any ideas let me know. As Will had mentioned it would be
good to have a common function table all these devices could use too. I
will take a closer look at what you have.

Cheers
Jon

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