[PATCH net-next v3 08/10] net: stmmac: dwmac-rk: add SGMII support for RK3568

[Coia Prant]

Maxime Chevallier <maxime.chevallier at bootlin.com> 于2026年9月3日周四 16:34写道：
>
> Hi
>
> On 9/1/26 17:01, Coia Prant wrote:
> > The RK3568 SoC integrates a Synopsys DesignWare XPCS that can be
> > connected to GMAC0 or GMAC1 in SGMII mode.  Add the necessary glue
> > logic to support this configuration.
> >
> > The current dwmac-rk driver does not support SGMII mode.  SGMII
> > requires a PCS to handle auto-negotiation and link state reporting,
> > but the existing driver only supports RGMII and RMII.
> >
> > Add a set_to_sgmii() callback to configure the GMAC GRF register for
> > SGMII mode (bit 7 set, interface selection bits 4:6 cleared).  Also
> > add a supports_sgmii flag to indicate SGMII capability.
> >
> > Provide pcs_init/pcs_exit callbacks to create/destroy the XPCS via
> > xpcs_rk_create() from the Rockchip XPCS platform driver, and a
> > select_pcs callback to return the XPCS to phylink.
> >
> > While at it, fix the clock enable ordering in rk_gmac_powerup():
> > gmac_clk_enable() is now called before any register access, including
> > the SGMII mode setup path.  Previously SGMII mode would bypass the
> > clock enable via a goto, which could cause synchronous external abort
> > when accessing MAC registers with the clock domain disabled.
> >
> > Also clean up the error handling in rk_gmac_powerup() by using a
> > unified clk_disable label, and add error handling for the default
> > (unhandled interface) case.
> >
> > SGMII In-band vs Out-of-band
> > ============================
> > On RK3568, the MAC clock is fixed at 125 MHz and cannot be dynamically
> > changed by the stmmac core's set_clk_tx_rate callback.  In-band mode
> > works because the PCS handles rate adaptation internally.  Out-of-band
> > mode does not work because the MAC would need to change the clock rate
> > to 125/12.5/1.25 MHz for 1000/100/10 Mbps respectively, and the clock
> > is fixed.
> >
> > Enable default_an_inband for SGMII and disable the generic stmmac
> > set_clk_tx_rate callback.  This forces phylink to use in-band mode,
> > where the PCS is responsible for speed/duplex negotiation.  Without
> > this, the stmmac core would attempt to change the clock rate on speed
> > changes, causing TX to work but RX to fail.
> >
> > Link: https://dl.radxa.com/rock3/docs/hw/datasheet/Rockchip%20RK3568%20TRM%20Part1%20V1.1-20210301.pdf (Page 386)
> > Signed-off-by: Coia Prant <coiaprant at gmail.com>
>
> [...]
>
> > +static int rk_pcs_init(struct stmmac_priv *priv)
> > +{
> > +     struct device_node *np = priv->device->of_node;
> > +     struct device_node *pcs_node;
> > +     struct dw_xpcs *xpcs;
> > +
> > +     pcs_node = of_parse_phandle(np, "pcs-handle", 0);
> > +     if (!pcs_node)
> > +             return -ENODEV;
>
> Here aswell you make it mandatory to have a PCS, as the generic pcs logic
> introduced in patch 1 doesn't handle -ENODEV, it treats it as any other
> error.
>
> So, either you return 0 when there's no PCS (so that we don't break platforms
> that don't have one), or you handle -ENODEV gracefully in patch 1.
>
> Maxime
>

Hi,

Currently, `rk_pcs_init` is called only for SGMII, which requires a PCS.

As it stands, only the RK3568 supports SGMII, so we won't break anything here.

Best,
Coia