[openwrt/openwrt] lantiq: nand: don't yield while holding spinlock

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch openwrt-22.03:
https://git.openwrt.org/354ad1084a074392e72d61e68e9bdbf16b4b774b

commit 354ad1084a074392e72d61e68e9bdbf16b4b774b
Author: Thomas Nixon <tom at tomn.co.uk>
AuthorDate: Sun Mar 26 10:19:21 2023 +0000

    lantiq: nand: don't yield while holding spinlock
    
    The nand driver normally while waiting for the device to become ready;
    this is normally fine, but xway_nand holds the ebu_lock spinlock, and
    this can cause lockups if other threads which use ebu_lock are
    interleaved. Fix this by waiting instead of polling.
    
    This mainly showed up as crashes in ath9k_pci_owl_loader (see
    https://github.com/openwrt/openwrt/issues/9829 ), but turning on
    spinlock debugging shows this happening in other places too.
    
    This doesn't seem to measurably impact boot time.
    
    Tested on bt_homehub-v5a with 5.10 and 5.15.
    
    Signed-off-by: Thomas Nixon <tom at tomn.co.uk>
    [Add commit description into patch]
    Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
    (cherry picked from commit d3b47909b199b876f67a0387b5545cb73bd6b815)
---
 ...d-xway-don-t-yield-while-holding-spinlock.patch | 38 ++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/target/linux/lantiq/patches-5.10/0400-mtd-rawnand-xway-don-t-yield-while-holding-spinlock.patch b/target/linux/lantiq/patches-5.10/0400-mtd-rawnand-xway-don-t-yield-while-holding-spinlock.patch
new file mode 100644
index 0000000000..edf0626860
--- /dev/null
+++ b/target/linux/lantiq/patches-5.10/0400-mtd-rawnand-xway-don-t-yield-while-holding-spinlock.patch
@@ -0,0 +1,38 @@
+From 416f25a948d11ef15733f2e31658d31b5cc7bef6 Mon Sep 17 00:00:00 2001
+From: Thomas Nixon <tom at tomn.co.uk>
+Date: Sun, 26 Mar 2023 11:08:49 +0100
+Subject: [PATCH] mtd: rawnand: xway: don't yield while holding spinlock
+
+The nand driver normally while waiting for the device to become ready;
+this is normally fine, but xway_nand holds the ebu_lock spinlock, and
+this can cause lockups if other threads which use ebu_lock are
+interleaved. Fix this by waiting instead of polling.
+
+This mainly showed up as crashes in ath9k_pci_owl_loader (see
+https://github.com/openwrt/openwrt/issues/9829 ), but turning on
+spinlock debugging shows this happening in other places too.
+
+This doesn't seem to measurably impact boot time.
+
+Signed-off-by: Thomas Nixon <tom at tomn.co.uk>
+---
+ drivers/mtd/nand/raw/xway_nand.c | 8 +++++++-
+ 1 file changed, 7 insertions(+), 1 deletion(-)
+
+--- a/drivers/mtd/nand/raw/xway_nand.c
++++ b/drivers/mtd/nand/raw/xway_nand.c
+@@ -175,7 +175,13 @@ static void xway_cmd_ctrl(struct nand_ch
+ 
+ static int xway_dev_ready(struct nand_chip *chip)
+ {
+-	return ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_RD;
++	/*
++	 * wait until ready, as otherwise the driver will yield in nand_wait or
++	 * nand_wait_ready, which is a bad idea when we're holding ebu_lock
++	 */
++	while ((ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_RD) == 0)
++		cpu_relax();
++	return 1;
+ }
+ 
+ static unsigned char xway_read_byte(struct nand_chip *chip)