Messages in this thread | | | Date | Fri, 19 Nov 2021 20:49:53 +0530 | Subject | Re: [PATCHv4 1/2] tracing: Add register read/write tracing support | From | Sai Prakash Ranjan <> |
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On 11/19/2021 7:47 PM, Marc Zyngier wrote: > On Fri, 19 Nov 2021 14:07:09 +0000, > Sai Prakash Ranjan <quic_saipraka@quicinc.com> wrote: >> On 11/19/2021 7:13 PM, Marc Zyngier wrote: >>> On Mon, 15 Nov 2021 11:33:29 +0000, >>> Sai Prakash Ranjan <quic_saipraka@quicinc.com> wrote: >>>> From: Prasad Sodagudi <psodagud@codeaurora.org> >>>> > [...] > >>>> Reason why we wouldn't need value along with mmio write log is >>>> that value can be easily deduced from the caller_name+offset which is >>>> printed already by the rwmmio trace events which gives the exact >>>> location of mmio writes and the value is easily known from the driver. >>> That's a very narrow view of what can be written in an MMIO >>> registers. We write dynamic values at all times, and if we are able to >>> trace MMIO writes, then the value written out must be part of the trace. >>> >>> I'd rather you try and get to the bottom of this issue rather than >>> paper over it. >>> >>> Thanks, >>> >>> M. >>> >> Sure, idea was to put it out in the open if anyone has any idea as >> to what might be happening there since the version where directly >> instrumenting the raw read/write accessors in arm64/asm/io.h was >> working fine casting doubts if this has to do something with >> inlining as Arnd mentioned before. > Yup. I wouldn't be surprised if MMIO accessors were getting directly > inlined at the wrong location and creating havoc. For example: > > writel(readl(addr1) | 1, addr2); > > If you're not careful about capturing the result of the read rather > than the read itself, you can end-up with something really funky. No > idea if that's what is happening, but a disassembly of the generated > code could tell you. > > M. >
I did that initially (compare the disassembly in working and non-working case) but didn't find anything noticeable, maybe I need to look some more. Thanks for the suggestion.
Thanks, Sai
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