Re: Coresight causes synchronous external abort on msm8916

From: Stephan Gerhold <stephan@gerhold.net>
To: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: agross@kernel.org, david.brown@linaro.org,
	mathieu.poirier@linaro.org, linux-arm-msm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: Coresight causes synchronous external abort on msm8916
Date: Wed, 19 Jun 2019 20:39:04 +0200	[thread overview]
Message-ID: <20190619183904.GB937@gerhold.net> (raw)
In-Reply-To: <a51f117f-c48d-d3f4-c3d1-9b584e3a055f@arm.com>

Hi,

On Wed, Jun 19, 2019 at 09:49:03AM +0100, Suzuki K Poulose wrote:
> Hi Stephan,
> 
> On 18/06/2019 21:26, Stephan Gerhold wrote:
> > Hi,
> > 
> > I'm trying to run mainline Linux on a smartphone with MSM8916 SoC.
> > It works surprisingly well, but the coresight devices seem to cause the
> > following crash shortly after userspace starts:
> > 
> >      Internal error: synchronous external abort: 96000010 [#1] PREEMPT SMP
> 
> ...
> 
> 
> > 
> > In this case I'm using a simple device tree similar to apq8016-sbc,
> > but it also happens using something as simple as msm8916-mtp.dts
> > on this particular device.
> >    (Attached: dmesg log with msm8916-mtp.dts and arm64 defconfig)
> > 
> > I can avoid the crash and boot without any further problems by disabling
> > every coresight device defined in msm8916.dtsi, e.g.:
> > 
> > 	tpiu@820000 { status = "disabled"; };
> 
> ...
> 
> > 
> > I don't have any use for coresight at the moment,
> > but it seems somewhat odd to put this in the device specific dts.
> > 
> > Any idea what could be causing this crash?
> 
> This is mostly due to the missing power domain support. The CoreSight
> components are usually in a debug power domain. So unless that is turned on,
> (either by specifying proper power domain ids for power management protocol
> supported by the firmware OR via other hacks - e.g, connecting a DS-5 to
> keep the debug power domain turned on , this works on Juno -).

Interesting, thanks a lot!

In this case I'm wondering how it works on the Dragonboard 410c.
Does it enable these power domains in the firmware?
  (Assuming it boots without this error...)

If coresight is not working properly on all/most msm8916 devices,
shouldn't coresight be disabled by default in msm8916.dtsi?
At least until those power domains can be set up by the kernel.

If this is a device-specific issue, what would be an acceptable solution
for mainline?
Can I turn on these power domains from the kernel?
Or is it fine to disable coresight for this device with the snippet above?

I'm not actually trying to use coresight, I just want the device to boot :)
And since I am considering submitting my device tree for inclusion in
mainline, I want to ask in advance how I should tackle this problem.

Thanks!
Stephan