• Larry Finger's avatar
    rtlwifi: rtl8821ae: Fix connection lost problem correctly · c713fb07
    Larry Finger authored
    There has been a coding error in rtl8821ae since it was first introduced,
    namely that an 8-bit register was read using a 16-bit read in
    _rtl8821ae_dbi_read(). This error was fixed with commit 40b368af
    ("rtlwifi: Fix alignment issues"); however, this change led to
    instability in the connection. To restore stability, this change
    was reverted in commit b8b8b163 ("rtlwifi: rtl8821ae: Fix connection
    lost problem").
    
    Unfortunately, the unaligned access causes machine checks in ARM
    architecture, and we were finally forced to find the actual cause of the
    problem on x86 platforms. Following a suggestion from Pkshih
    <pkshih@realtek.com>, it was found that increasing the ASPM L1
    latency from 0 to 7 fixed the instability. This parameter was varied to
    see if a smaller value would work; however, it appears that 7 is the
    safest value. A new symbol is defined for this quantity, thus it can be
    easily changed if necessary.
    
    Fixes: b8b8b163 ("rtlwifi: rtl8821ae: Fix connection lost problem")
    Cc: Stable <stable@vger.kernel.org> # 4.14+
    Fix-suggested-by: default avatarPkshih <pkshih@realtek.com>
    Signed-off-by: default avatarLarry Finger <Larry.Finger@lwfinger.net>
    Tested-by: James Cameron <quozl@laptop.org>  # x86_64 OLPC NL3
    Signed-off-by: default avatarKalle Valo <kvalo@codeaurora.org>
    c713fb07
hw.c 118 KB