Re: [PATCH v3 2/2] net: stmmac: imx: Disable EEE

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Mon, Mar 23, 2026 at 11:39:33AM +0200, Laurent Pinchart wrote:
> The i.MX8MP suffers from an interrupt storm related to the stmmac and
> EEE. A long and tedious analysis ([1]) concluded that the SoC wires the
> stmmac lpi_intr_o signal to an OR gate along with the main dwmac
> interrupts, which causes an interrupt storm for two reasons.
> 
> First, there's a race condition due to the interrupt deassertion being
> synchronous to the RX clock domain:
> 
> - When the PHY exits LPI mode, it restarts generating the RX clock
>   (clk_rx_i input signal to the GMAC).
> - The MAC detects exit from LPI, and asserts lpi_intr_o. This triggers
>   the ENET_EQOS interrupt.
> - Before the CPU has time to process the interrupt, the PHY enters LPI
>   mode again, and stops generating the RX clock.
> - The CPU processes the interrupt and reads the GMAC4_LPI_CTRL_STATUS
>   registers. This does not clear lpi_intr_o as there's no clk_rx_i.
> 
> An attempt was made to fixing the issue by not stopping RX_CLK in Rx LPI
> state ([2]). This alleviates the symptoms but doesn't fix the issue.
> Since lpi_intr_o takes four RX_CLK cycles to clear, an interrupt storm
> can still occur during that window. In 1000T mode this is harder to
> notice, but slower receive clocks cause hundreds to thousands of
> spurious interrupts.
> 
> Fix the issue by disabling EEE completely on i.MX8MP.
> 
> [1] https://lore.kernel.org/all/20251026122905.29028-1-laurent.pinchart@ideasonboard.com/
> [2] https://lore.kernel.org/all/20251123053518.8478-1-laurent.pinchart@ideasonboard.com/
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Thanks!

-- 
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