linux: add bc250 audio patch by essdee

The PS5 GbE NIC has no INTx pin and its MSI sometimes never fires after a
cold boot. The driver already works around that with a 1 Hz link-poll
watchdog that kicks NAPI by hand.

But gbe_poll() re-checks GBE_REG_ISR after completing NAPI and reschedules
itself whenever a GBE_IER_MASK cause is still latched, without ever
acknowledging (W1C) the ISR -- only the hardware handler gbe_isr() does.
When the MSI is dead gbe_isr() never runs, so the latched cause (e.g.
RX_DONE) is never cleared, the re-check stays true forever, and NAPI
reschedules itself ~30k times/s, pinning ksoftirqd on that CPU at 100%.

Acknowledge the pending causes before re-kicking so a stale, undelivered
cause can no longer spin NAPI.

While the MSI is dead also poll the rings every GBE_POLL_FALLBACK_MS (10 ms)
instead of once per second, so interactive RX latency drops from ~1 s to a
few ms; fall back to HZ as soon as real IRQs start arriving.

README.md

@@ -6,7 +6,7 @@
 git clone https://github.com/ps5-linux/ps5-linux-patches
 git clone https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
 cd linux
-git checkout tags/v7.0.10
+git checkout "tags/v$(grep -m1 "^# Linux/" ../ps5-linux-patches/.config | awk '{print $3}')"
 git apply ../ps5-linux-patches/linux.patch
 cp ../ps5-linux-patches/.config .config
 make -j$(nproc)