linux-kernel - Re: CoreSight framework and drivers

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Message-ID: <20121221221252.GA22404@pratikp-linux.qualcomm.com>
Date:	Fri, 21 Dec 2012 14:12:53 -0800
From:	Pratik Patel <pratikp@...eaurora.org>
To:	Jean Pihet <jean.pihet@...oldbits.com>
Cc:	Jon Hunter <jon-hunter@...com>,
	"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>,
	LKML <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 Thu, Dec 20, 2012 at 09:16:15PM +0100, Jean Pihet wrote:
> Hi Pratik,
> 
> On Thu, Dec 20, 2012 at 8:51 PM, Pratik Patel <pratikp@...eaurora.org> 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?
> >
> >> 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.
> I am also interested to look at such a framework in order to have a
> clean implementation of the ETM, PMI/CMI (HW tracing IP on OMAP4+).
> I am currently busy on a driver for PMI/CMI which requires some
> configuration of the Coresight, ETM, ETB, ATB etc. IP blocks.
> 
> Could you send your patches to linux-arm and linux-omap mailing lists?
> I will be pleased to review them.
> 

Thanks. I did post them to linux-arm-kernel but they are waiting
on moderator approval. Hopefully they will get posted soon.

-- 
Employee of Qualcomm Innovation Center, Inc.
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