On Wed, Aug 16, 2023 at 10:46:01PM +0530, Manivannan Sadhasivam wrote: > On Wed, Aug 16, 2023 at 12:25:50PM -0400, Radu Rendec wrote: > > On Tue, 2023-08-15 at 11:54 +0100, Bryan O'Donoghue wrote: > > > On 14/08/2023 23:36, Radu Rendec wrote: > > > > I'm consistently getting a system crash followed by a ramdump on > > > > sa8540p-ride (sc8280xp) when icc_sync_state() goes all the way through > > > > (count == providers_count). > > > > > > > > Context: all PCIe buses are disabled due to [1]. Previously, due to > > > > some local kernel misconfiguration, icc_sync_state() never really did > > > > anything (because count was always less than providers_count). > > > > > > > > I was able to isolate the problem to the qns_pcie_gem_noc icc node. > > > > What happens is that both avg_bw and peak_bw for this node end up as 0 > > > > after aggregate_requests() gets called. The request list associated > > > > with the node is empty. > > > > > > If all PCIe buses are disabled, then of course the bandwidth requests > > > should say zero, the clocks should be disabled and any associated > > > regulators should be off. > > > > > > > For testing purposes, I modified icc_sync_state() to skip calling > > > > aggregate_requests() and subsequently p->set(n, n) for that particular > > > > node only. With that change in place, the system no longer crashes. > > > > > > So what's happening is that a bus master in the system - perhaps not the > > > application processor is issuing a transaction to a register most likely > > > that is not clocked/powered. > > > > Yes, that was my assumption as well. But I didn't think it could be > > something other than the AP. That is an interesting perspective. > > > > My first thought was to analyze the ramdump and hopefully find some > > clues there. But unfortunately that doesn't seem to be an option with > > the tools that I have. > > > > > Have you considered that one of the downstream devices might be causing > > > a PCIe bus transaction ? > > > > No, I haven't considered that. If that's the case, it will probably be > > even harder to debug. > > > > If the PCIe controller node is disabled in devicetree, then none of the devices > would be enumerated. In that case, they cannot initiate any transactions on > their own. > > Qcom observed a similar crash with PCIe SMMU when the PCIe controllers were not > enabled in devicetree [1]. Since Qcom was going to enable PCIe controllers > eventually, I concluded that the issue will be gone once they do it. > > But looking at your issue, I think the transaction is triggered by PCIe SMMU as > observed earlier. Since there are no active votes on the path after > icc_sync_state(), it ends up in a crash. > > But did you disable all PCIe instances or just pcie2a? The revert patch you > pointed only applies to pcie2a. But if you are disabling all PCIe instances, > then I do not see a point in enabling PCIe SMMU as well. Could you try disabling > the pcie_smmu node and check? I think this is a good hunch, but do note that this is discussing sa8540p-ride, not sa8775p-ride. The former has no PCIe SMMU described (although I believe there maybe one on the sc8280xp family, just in "bypass mode" (excuse my SMMU ignorance!) by firmware, and not described to Linux for any variant of that platform). > > - Mani > > [1] https://lore.kernel.org/linux-arm-msm/20230609054141.18938-3-quic_ppareek@xxxxxxxxxxx/ > > > > If you physically remove - can you physically remove - devices from the > > > PCIe bus does this error still occur ? > > > > This is a standard QDrive 3 reference board, so I think this is not an > > option. Taking those things apart is very difficult, and I think all > > peripherals are soldered onto the board anyway. > > > > > > Surprisingly, none of the icc nodes that link to qns_pcie_gem_noc (e.g. > > > > xm_pcie3_0, xm_pcie3_1, etc.) has any associated request and so they > > > > all have 0 bandwidth after aggregate_requests() gets called, but that > > > > doesn't seem to be a problem and the system is stable. This makes me > > > > think there is a missing link somewhere, and something doesn't claim > > > > any bandwidth on qns_pcie_gem_noc when it should. And it's probably > > > > none of the xm_pcie3_* nodes, since setting their bandwidth to 0 seems > > > > to be fine. > > > > > > Yes so if you assume that the AP/kernel side has the right references, > > > counts, votes then consider another bus master - a thing that can > > > initiate a read or a write might be misbehaving. > > > > There is one thing I wasn't aware of when I wrote the previous email. > > As it turns out, bandwidth/clock control is done at the bcm level, not > > at the icc node level. It looks like there is a single bcm called PCI0, > > and it's linked to the qns_pcie_gem_noc node. The xm_pcie3_* icc nodes > > are not linked to any bcm. > > > > This means that *all* PCIe buses are shut down when qns_pcie_gem_noc is > > disabled due to zero bandwidth. I was under the (wrong) impression > > that, since all xm_pcie3_* nodes had no requests, each corresponding > > PCIe bus would be shut down separately, leaving only qns_pcie_gem_noc > > active (with my test change in place). > > > > > Assuming there is no misbehaving arm core - say a cDSP or aDSP piece of > > > code that wants to do something on the PCIe bus, might the culprit be > > > whatever you have connected to the bus ? > > > > > > Could something be driving the #WAKE signal and then transacting ? > > > > > > But also keep in mind depending on what you are doing with this system > > > if you have a bit of firmware in one of the DSP cores - does that > > > firmware have scope to talk to any devices on the PCIe bus ? > > > > As I mentioned above, this is a standard QDrive 3 reference board. > > Furthermore, I don't explicitly do anything with the DSPs. I just boot > > a fairly recent upstream kernel (6.5-rc1) with a standard rootfs. The > > boot firmware is whatever Qualcomm provides by default for these > > systems. So, unless the boot firmware loads anything into the DSPs > > behind my back (which I doubt), the DSPs should not even be running. > > > > What is more likely though is that the boot firmware initializes a > > bunch of PCIe devices and leaves them on. > > > > > I'd guess another firmware is unlikely but, a downstream device doing a > > > #WAKE when you have the PCIe nodes disabled would presumably be bad.. > > > > > > Try looking for an upstream transaction from a device.. > > > > Yes, that makes sense. Do you have any suggestion on how to do that > > without using any specialized hardware (such as JTAG pod or PCIe bus > > analyzer)? > > > > Thanks for all the input and suggestions! > > > > -- > > Radu > > > > -- > மணிவண்ணன் சதாசிவம் >
