net: dsa: ks8995: Add proper RESET delay

According to the datasheet we need to wait 100us before accessing
any registers in the KS8995 after a reset de-assertion.

Add this delay, if and only if we obtained a GPIO descriptor,
otherwise it is just a pointless delay.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250813-ks8995-to-dsa-v1-2-75c359ede3a5@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/dsa/ks8995.c b/drivers/net/dsa/ks8995.c
index d135b061d810b7ba0c0731d43d176f3ba46b3f52..bdee8c62315f336e380313558c66127ff0b701d3 100644 (file)
--- a/drivers/net/dsa/ks8995.c
+++ b/drivers/net/dsa/ks8995.c
@@ -438,9 +438,15 @@ static int ks8995_probe(struct spi_device *spi)
        if (err)
                return err;
 
-       /* de-assert switch reset */
-       /* FIXME: this likely requires a delay */
-       gpiod_set_value_cansleep(ks->reset_gpio, 0);
+       if (ks->reset_gpio) {
+               /*
+                * If a reset line was obtained, wait for 100us after
+                * de-asserting RESET before accessing any registers, see
+                * the KS8995MA datasheet, page 44.
+                */
+               gpiod_set_value_cansleep(ks->reset_gpio, 0);
+               udelay(100);
+       }
 
        spi_set_drvdata(spi, ks);