Messages in this thread | | | Date | Fri, 19 Nov 2021 19:37:09 +0530 | Subject | Re: [PATCHv4 1/2] tracing: Add register read/write tracing support | From | Sai Prakash Ranjan <> |
| |
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> >> >> Generic MMIO read/write i.e., __raw_{read,write}{b,l,w,q} accessors >> are typically used to read/write from/to memory mapped registers >> and can cause hangs or some undefined behaviour in following few >> cases, >> >> * If the access to the register space is unclocked, for example: if >> there is an access to multimedia(MM) block registers without MM >> clocks. >> >> * If the register space is protected and not set to be accessible from >> non-secure world, for example: only EL3 (EL: Exception level) access >> is allowed and any EL2/EL1 access is forbidden. >> >> * If xPU(memory/register protection units) is controlling access to >> certain memory/register space for specific clients. >> >> and more... >> >> Such cases usually results in instant reboot/SErrors/NOC or interconnect >> hangs and tracing these register accesses can be very helpful to debug >> such issues during initial development stages and also in later stages. >> >> So use ftrace trace events to log such MMIO register accesses which >> provides rich feature set such as early enablement of trace events, >> filtering capability, dumping ftrace logs on console and many more. >> >> Sample output: >> >> rwmmio_read: gic_peek_irq+0xd0/0xd8 readl addr=0xffff800010040104 >> rwmmio_write: gic_poke_irq+0xe4/0xf0 writel addr=0xffff800010040184 >> rwmmio_read: gic_do_wait_for_rwp+0x54/0x90 readl addr=0xffff800010040000 >> rwmmio_write: gic_set_affinity+0x1bc/0x1e8 writeq addr=0xffff800010046130 >> >> Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org> >> [saiprakash: Rewrote commit msg and trace event field edits] >> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com> >> --- >> >> Have dropped value parameter for mmio write trace event as that >> was causing hangs in strange ways, i.e., if we pass any other >> 64bit value, it works fine but passing value would just hang. >> Not just using the log apis, even simple trace_printk with value >> printed would cause hang. It wasn't noticed in early version >> because dyndbg would filter the logging in my system (I had >> set it to trace only specific qcom directory) but once this >> version starts recording all the reads/writes with value passed, >> it just hangs system when rwmmio write event tracing is enabled. > Why is that so? Not being able to track the value written out makes > the feature pretty useless if you're not writing fixed values. > >> 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.
Thanks, Sai
| |