[PATCH net-next v4 1/2] net: stmmac: provide flag to disable EEE

[Laurent Pinchart]

On Wed, Mar 25, 2026 at 11:00:02PM +0200, Laurent Pinchart wrote:
> From: "Russell King (Oracle)" <rmk+kernel at armlinux.org.uk>
> 
> Some platforms have problems when EEE is enabled, and thus need a way
> to disable stmmac EEE support. Add a flag before the other LPI related
> flags which tells stmmac to avoid populating the phylink LPI
> capabilities, which causes phylink to call phy_disable_eee() for any
> PHY that is attached to the affected phylink instance.
> 
> iMX8MP is an example - the lpi_intr_o signal is wired to an OR gate
> along with the main dwmac interrupts. Since lpi_intr_o is synchronous
> to the receive clock domain, and takes four clock cycles to clear, this
> leads to interrupt storms as the interrupt remains asserted for some
> time after the LPI control and status register is read.
> 
> This problem becomes worse when the receive clock from the PHY stops
> when the receive path enters LPI state - which means that lpi_intr_o
> can not deassert until the clock restarts. Since the LPI state of the
> receive path depends on the link partner, this is out of our control.
> We could disable RX clock stop at the PHY, but that doesn't get around
> the slow-to-deassert lpi_intr_o mentioned in the above paragraph.
> 
> Previously, iMX8MP worked around this by disabling gigabit EEE, but
> this is insufficient - the problem is also visible at 100M speeds,
> where the receive clock is slower.
> 
> There is extensive discussion and investigation in the thread linked
> below, the result of which is summarised in this commit message.
> 
> Reported-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Closes: https://lore.kernel.org/r/20251026122905.29028-1-laurent.pinchart@ideasonboard.com
> Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
> Tested-by: Ovidiu Panait <ovidiu.panait.rb at renesas.com>

And I just realized I haven't sent an R-b tag, despite having reviewed
the patch.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |  7 ++++++-
>  include/linux/stmmac.h                            | 13 +++++++------
>  2 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 9b6b49331639..ce51b9c22129 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -1438,7 +1438,12 @@ static int stmmac_phylink_setup(struct stmmac_priv *priv)
>  				 config->supported_interfaces,
>  				 pcs->supported_interfaces);
>  
> -	if (priv->dma_cap.eee) {
> +	/* Some platforms, e.g. iMX8MP, wire lpi_intr_o to the same interrupt
> +	 * used for stmmac's main interrupts, which leads to interrupt storms.
> +	 * STMMAC_FLAG_EEE_DISABLE allows EEE to be disabled on such platforms.
> +	 */
> +	if (priv->dma_cap.eee &&
> +	    !(priv->plat->flags & STMMAC_FLAG_EEE_DISABLE)) {
>  		/* The GMAC 3.74a databook states that EEE is only supported
>  		 * in MII, GMII, and RGMII interfaces.
>  		 */
> diff --git a/include/linux/stmmac.h b/include/linux/stmmac.h
> index 5b2bece81448..e62d21afd56d 100644
> --- a/include/linux/stmmac.h
> +++ b/include/linux/stmmac.h
> @@ -207,12 +207,13 @@ enum dwmac_core_type {
>  #define STMMAC_FLAG_MULTI_MSI_EN		BIT(7)
>  #define STMMAC_FLAG_EXT_SNAPSHOT_EN		BIT(8)
>  #define STMMAC_FLAG_INT_SNAPSHOT_EN		BIT(9)
> -#define STMMAC_FLAG_RX_CLK_RUNS_IN_LPI		BIT(10)
> -#define STMMAC_FLAG_EN_TX_LPI_CLOCKGATING	BIT(11)
> -#define STMMAC_FLAG_EN_TX_LPI_CLK_PHY_CAP	BIT(12)
> -#define STMMAC_FLAG_HWTSTAMP_CORRECT_LATENCY	BIT(13)
> -#define STMMAC_FLAG_KEEP_PREAMBLE_BEFORE_SFD	BIT(14)
> -#define STMMAC_FLAG_SERDES_SUPPORTS_2500M	BIT(15)
> +#define STMMAC_FLAG_EEE_DISABLE			BIT(10)
> +#define STMMAC_FLAG_RX_CLK_RUNS_IN_LPI		BIT(11)
> +#define STMMAC_FLAG_EN_TX_LPI_CLOCKGATING	BIT(12)
> +#define STMMAC_FLAG_EN_TX_LPI_CLK_PHY_CAP	BIT(13)
> +#define STMMAC_FLAG_HWTSTAMP_CORRECT_LATENCY	BIT(14)
> +#define STMMAC_FLAG_KEEP_PREAMBLE_BEFORE_SFD	BIT(15)
> +#define STMMAC_FLAG_SERDES_SUPPORTS_2500M	BIT(16)
>  
>  struct mac_device_info;
>  

-- 
Regards,

Laurent Pinchart