target/linux/lantiq/patches-5.10/0400-mtd-rawnand-xway-don-t-yield-while-holding-spinlock.patch

   1 From 416f25a948d11ef15733f2e31658d31b5cc7bef6 Mon Sep 17 00:00:00 2001
   2 From: Thomas Nixon <tom@tomn.co.uk>
   3 Date: Sun, 26 Mar 2023 11:08:49 +0100
   4 Subject: [PATCH] mtd: rawnand: xway: don't yield while holding spinlock
   5
   6 The nand driver normally while waiting for the device to become ready;
   7 this is normally fine, but xway_nand holds the ebu_lock spinlock, and
   8 this can cause lockups if other threads which use ebu_lock are
   9 interleaved. Fix this by waiting instead of polling.
  10
  11 This mainly showed up as crashes in ath9k_pci_owl_loader (see
  12 https://github.com/openwrt/openwrt/issues/9829 ), but turning on
  13 spinlock debugging shows this happening in other places too.
  14
  15 This doesn't seem to measurably impact boot time.
  16
  17 Signed-off-by: Thomas Nixon <tom@tomn.co.uk>
  18 ---
  19  drivers/mtd/nand/raw/xway_nand.c | 8 +++++++-
  20  1 file changed, 7 insertions(+), 1 deletion(-)
  21
  22 --- a/drivers/mtd/nand/raw/xway_nand.c
  23 +++ b/drivers/mtd/nand/raw/xway_nand.c
  24 @@ -175,7 +175,13 @@ static void xway_cmd_ctrl(struct nand_ch
  25
  26  static int xway_dev_ready(struct nand_chip *chip)
  27  {
  28 -       return ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_RD;
  29 +       /*
  30 +        * wait until ready, as otherwise the driver will yield in nand_wait or
  31 +        * nand_wait_ready, which is a bad idea when we're holding ebu_lock
  32 +        */
  33 +       while ((ltq_ebu_r32(EBU_NAND_WAIT) & NAND_WAIT_RD) == 0)
  34 +               cpu_relax();
  35 +       return 1;
  36  }
  37
  38  static unsigned char xway_read_byte(struct nand_chip *chip)