Okay, I need to figure out why the user's QEMU setup isn't working correctly, especially since they're encountering a problem related to the FDT rendering in their SPAPR setup. They provided some commit information and a QEMU command line. Looking at their git bisect output, it seems that when they introduced the full FDT rendering on ibm,client-architecture-support (commit e68cd0cb5), things started breaking. The first bad commit is that one. Before that, everything was working fine with the other changes like setting DFP functions and removing unnecessary ifs. I remember that in QEMU, the FDT (Flattened Device Tree) is crucial for PPC systems as it describes the hardware to the guest OS. If the FDT isn't rendered correctly, the guest might not initialize hardware properly, leading to crashes or hangs. So, focusing on commit e68cd0cb5: the user modified the code to render the full FDT. Maybe this introduced a regression because some parts of the device tree weren't handled correctly anymore. Perhaps certain nodes were being omitted or improperly formatted. Looking at their QEMU command line, they're using a pseries-4.2 machine type with KVM acceleration. They've disabled USB and set up a lot of memory (81920 MB) and 512 vCPUs in a single socket with 128 cores and 4 threads each. That's a pretty heavy setup, so any issue might be more noticeable. I also notice they're using VirtIO devices for SCSI and network, which should be fine as long as the FDT correctly includes the necessary information for these devices. The serial is set up via SPAPR-VTY, which again depends on the FDT being correct. So, the problem likely stems from the FDT rendering changes. Maybe certain properties or nodes were added that aren't compatible with their specific setup or perhaps there's a bug in how the FDT is constructed now. I should think about possible issues in the FDT generation after this commit. Perhaps some compatibility parameters are missing, or there might be an error in the device tree structure that causes the guest to misread it. Another angle: maybe the way QEMU handles certain hardware components changed with the full FDT rendering. For example, if they were relying on older FDT structures that didn't include all necessary nodes, the new structure could cause issues with device enumeration or driver loading in the guest OS. Alternatively, perhaps there's a bug in how the commit e68cd0cb5 interacts with other parts of the code, especially when dealing with large memory setups and many vCPUs. Maybe some initialization steps were overlooked, leading to an incomplete or corrupted FDT. To diagnose further, I could check if any QEMU error messages are present related to device tree issues. Also, verifying that all expected nodes are correctly included in the generated FDT after this commit would be helpful. Comparing the old and new FDTs might reveal missing or added nodes that cause compatibility problems. In summary, the user's issue is likely due to incorrect FDT rendering introduced by commit e68cd0cb5, which broke their specific setup involving a large PPC system with multiple VirtIO devices. To fix it, they might need to adjust how the FDT is generated or revert to an older version where the FDT rendering was handled correctly for their environment. Based on the information provided and the git bisect output, the issue appears to be related to the commit where the full FDT (Flattened Device Tree) rendering was introduced. The commit `e68cd0cb5cf49d334abe17231a1d2c28b846afa2` (`spapr: Render full FDT on ibm,client-architecture-support`) is identified as the first bad commit. ### Key Observations: 1. **Good Commits**: - `33432d7737b53c92791f90ece5dbe3b7bb1c79f5`: Introduced helper functions for setting DFP (Decimal Floating Point) in PPC. - `f6d4c423a222f02bfa84a49c3d306d7341ec9bab`: Removed unnecessary if() conditions around calls to the DFP helper functions. - `c4ec08ab70bab90685d1443d6da47293e3aa312a`: Stopped providing assigned-addresses in spapr-pci. 2. **Bad Commit**: - `e68cd0cb5cf49d334abe17231a1d2c28b846afa2`: Introduced rendering of the full FDT on ibm,client-architecture-support. This commit is identified as the first bad commit. ### Likely Cause: The issue likely stems from changes in how the FDT (Flattened Device Tree) is being rendered for SPAPR systems. The FDT is crucial for describing hardware to the guest operating system in PowerPC (PPC) environments. Incorrect rendering of the FDT can lead to hardware initialization failures, leading to crashes or hangs. ### Recommendations: 1. **Revert the Bad Commit**: - If the full FDT rendering introduced a regression, consider reverting the commit `e68cd0cb5cf49d334abe17231a1d2c28b846afa2` to restore functionality. 2. **Investigate the FDT Rendering**: - Review how the FDT is being generated in this commit and ensure that all necessary nodes and properties are correctly included. - Compare the FDT structure before and after this commit to identify any missing or incorrectly formatted nodes. 3. **Verify Compatibility**: - Ensure that the changes in FDT rendering are compatible with the specific hardware configuration being used (e.g., VirtIO devices, network interfaces, etc.). 4. **Log Analysis**: - Check QEMU logs for more detailed error messages related to device tree initialization or hardware setup. ### Conclusion: The issue is likely due to incorrect or incomplete rendering of the FDT introduced by commit `e68cd0cb5`. Reverting this commit or fixing the FDT generation should resolve the problem.