diff --git a/hosts/common/boot.nix b/hosts/common/boot.nix
index a384bd41f..9204c0f22 100644
--- a/hosts/common/boot.nix
+++ b/hosts/common/boot.nix
@@ -28,6 +28,7 @@
   # simpler to keep near the latest kernel on all devices,
   # and also makes certain that any weird system-level bugs i see aren't likely to be stale kernel bugs.
   boot.kernelPackages = lib.mkDefault pkgs.linuxPackages_latest;
+  # boot.kernelPackages = lib.mkDefault pkgs.linuxPackages_testing;
 
   # hack in the `boot.shell_on_fail` arg since that doesn't always seem to work.
   boot.initrd.preFailCommands = "allowShell=1";
diff --git a/hosts/modules/hal/pine64-pinephone-pro/default.nix b/hosts/modules/hal/pine64-pinephone-pro/default.nix
index 65caadd60..8b346c346 100644
--- a/hosts/modules/hal/pine64-pinephone-pro/default.nix
+++ b/hosts/modules/hal/pine64-pinephone-pro/default.nix
@@ -194,12 +194,14 @@ in
 
     boot.extraModulePackages = [
       config.boot.kernelPackages.rk818-charger  #< rk818 battery/charger isn't mainline as of 2024-10-01
-      config.boot.kernelPackages.imx258  #< mainline imx258 camera driver has some power-on issues on PPP  (imx258 1-001a: Error reading reg 0x0016: -6)
+      #v XXX(???? - 2025-07-18): mainline imx258 camera driver has some power-on issues on PPP  (imx258 1-001a: Error reading reg 0x0016: -6)
+      #v XXX(2025-07-18): megi's imx258 breaks mainline audio, though
+      # config.boot.kernelPackages.imx258
       #v optionally use megi's rt5640 sound driver;
-      #v XXX(2025-07-18): mainline driver errors: `rt5640: 1-001c: ASoC error (-22): at snd_soc_dai_set_sysclk() on rt5640-aif1`
+      #v XXX(2025-07-18): when using megi's imx258, the mainline rt5640 driver errors: `rt5640: 1-001c: ASoC error (-22): at snd_soc_dai_set_sysclk() on rt5640-aif1`
       #v                  prior to this mainline driver was working fine, alongside camera/imx258, for half a year.
       #v                  although this fixes the dmesg errors, it causes pipewire/wireplumber to crash-loop.
-      config.boot.kernelPackages.rt5640
+      # config.boot.kernelPackages.rt5640
     ];
 
     # default nixos behavior is to error if a kernel module is provided by more than one package.
diff --git a/pkgs/by-name/nixpkgs-bootstrap/patches.nix b/pkgs/by-name/nixpkgs-bootstrap/patches.nix
index 4929f8056..589ea9f87 100644
--- a/pkgs/by-name/nixpkgs-bootstrap/patches.nix
+++ b/pkgs/by-name/nixpkgs-bootstrap/patches.nix
@@ -37,6 +37,31 @@ in
     hash = "sha256-Hs3uKT3b5D4hkipEgD19j+bv5k63Eba8jMdENaE1Plg=";
   })
 
+  # 2025-07-18: downgrade the kernel 6.15.7 -> 6.15.5.
+  # moby audio is broken by kernel > 6.15.5.
+  # dmesg:
+  # `rt5640: 1-001c: ASoC error (-22): at snd_soc_dai_set_sysclk() on rt5640-aif1`
+  # [repeats 5 times per second]
+  # (fetchpatch' {
+  #   revert = true;
+  #   name = "Kernel updates for 2025-07-17";  # linux: 6.15.6 -> 6.15.7
+  #   prUrl = "https://github.com/NixOS/nixpkgs/pull/426155";
+  #   hash = "sha256-lUXKTTklSVsQCjfLCb66sNKvsTHtxj+YyIrivUNdBKY=";
+  # })
+  # (fetchpatch' {
+  #   # required for 2025-07-10 reversion to apply
+  #   revert = true;
+  #   name = "Kernel updates for 2025-07-14";
+  #   prUrl = "https://github.com/NixOS/nixpkgs/pull/425140";
+  #   hash = "sha256-wbRmCnhVEFmscKW8pGGOE5oeLtEyMf4UxUQHznPVgR4=";
+  # })
+  # (fetchpatch' {
+  #   revert = true;
+  #   name = "Kernel updates for 2025-07-10";  # linux: 6.15.5 -> 6.15.6
+  #   prUrl = "https://github.com/NixOS/nixpkgs/pull/424079";
+  #   hash = "sha256-W469oV4FvK0IU1YktDGqbx+u5ZHfYFtJEnfefpM14G0=";
+  # })
+
   (fetchpatch' {
     # 2025-07-13: merged into staging
     # fixes cross compilation