linux-kernel - Re: [PATCH net] net: mdio-mux-meson-gxl: set RESERVED0 bit in REG2

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Message-ID: <1ja5v9q474.fsf@starbuckisacylon.baylibre.com>
Date:   Wed, 02 Aug 2023 09:43:38 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Da Xue <da@...re.computer>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: mdio-mux-meson-gxl: set RESERVED0 bit in REG2


On Tue 01 Aug 2023 at 16:34, Da Xue <da@...re.computer> wrote:

> The first RESERVED register bit needs to be set in order for the PHY
> to come up. Otherwise the ethernet device stays in "No Carrier".
> There's no associated documentation for this register bit in the
> Amlogic datasheets, only the default value to set for the entire
> register.
>
> This register bit is normally set in u-boot so it is not noticed in
> Linux. During my testing with u-boot net disabled, this problem crops
> up.
>
> Signed-off-by: Da Xue <da@...re.computer>

Reviewed-by: Jerome Brunet <jbrunet@...libre.com>

> ---
>  drivers/net/mdio/mdio-mux-meson-gxl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/mdio/mdio-mux-meson-gxl.c
> b/drivers/net/mdio/mdio-mux-meson-gxl.c
> index 76188575ca1f..210a52d98112 100644
> --- a/drivers/net/mdio/mdio-mux-meson-gxl.c
> +++ b/drivers/net/mdio/mdio-mux-meson-gxl.c
> @@ -17,6 +17,7 @@
>  #define  REG2_LEDACT           GENMASK(23, 22)
>  #define  REG2_LEDLINK          GENMASK(25, 24)
>  #define  REG2_DIV4SEL          BIT(27)
> +#define  REG2_RESERVED0                BIT(28)
>  #define  REG2_ADCBYPASS                BIT(30)
>  #define  REG2_CLKINSEL         BIT(31)
>  #define ETH_REG3               0x4
> @@ -65,7 +66,7 @@ static void gxl_enable_internal_mdio(struct
> gxl_mdio_mux *priv)
>          * The only constraint is that it must match the one in
>          * drivers/net/phy/meson-gxl.c to properly match the PHY.
>          */
> -       writel(FIELD_PREP(REG2_PHYID, EPHY_GXL_ID),
> +       writel(REG2_RESERVED0 | FIELD_PREP(REG2_PHYID, EPHY_GXL_ID),
>                priv->regs + ETH_REG2);
>
>         /* Enable the internal phy */