[openwrt/openwrt] ath79: fix packetloss on some WLR-7100

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch openwrt-22.03:
https://git.openwrt.org/92a0dd2447bda9a6d5440f4a94d9b617406e3f76

commit 92a0dd2447bda9a6d5440f4a94d9b617406e3f76
Author: Matthijs Kooijman <matthijs at stdin.nl>
AuthorDate: Thu Aug 31 21:10:23 2023 +0200

    ath79: fix packetloss on some WLR-7100
    
    On some WLR-7100 routers, significant packet loss was observed. This is
    fixed by configuring a delay on the GMAC0 RXD and RXDV lines.
    
    The values used in this commit are copied from the values used by the
    stock firmare (based on register dumping).
    
    Out of four test routers, the problem was consistently observed on two.
    It is unclear what the relevant difference is exactly (the two working
    routers were v1 001 with AR1022 and v1 002 with AR9342, the two broken
    routers were both v1 002 with AR1022). All PCB routing also seems
    identical, so maybe there is some stray capacitance on some of these
    that adds just enough delay or so...
    
    With this change, the packet loss disappears on the broken routers,
    without introducing new packet loss on the previously working routers.
    
    Note that the PHY *also* has delays enabled (through
    `qca,ar8327-initvals`) on both RX and TX lines, but apparently that is
    not enough, or it is not effective (registers have been verified to be
    written).
    
    For detailed discussion of this issue and debug history, see
    https://forum.openwrt.org/t/sitecom-wlr-7100-development-progress/79641
    
    Signed-off-by: Matthijs Kooijman <matthijs at stdin.nl>
    (cherry picked from commit d2ce3a61aa1cbc53988eb640cbab48e20fbfb1aa)
---
 target/linux/ath79/dts/ar1022_sitecom_wlr-7100.dts | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/target/linux/ath79/dts/ar1022_sitecom_wlr-7100.dts b/target/linux/ath79/dts/ar1022_sitecom_wlr-7100.dts
index d008dd5ec8..e2ccef105d 100644
--- a/target/linux/ath79/dts/ar1022_sitecom_wlr-7100.dts
+++ b/target/linux/ath79/dts/ar1022_sitecom_wlr-7100.dts
@@ -65,6 +65,8 @@
 	gmac-config {
 		device = <&gmac>;
 		rgmii-gmac0 = <1>;
+		rxdv-delay = <3>;
+		rxd-delay = <3>;
 	};
 };