Re: [PATCH net-next v3 06/15] net: macb: allocate tieoff descriptor once across device lifetime

[Nicolai Buchwitz <nb@tipi-net.de>]

Hi Théo

On 1.7.2026 17:59, Théo Lebrun wrote:
> The tieoff descriptor is a RX DMA descriptor ring of size one. It gets
> configured onto queues for Wake-on-LAN during system-wide suspend when
> hardware does not support disabling individual queues
> (MACB_CAPS_QUEUE_DISABLE).
> 
> MACB/GEM driver allocates it alongside the main RX ring
> inside macb_alloc() at open. Free is done by macb_free() at close.
> 
> Change to allocate once at probe and free on probe failure or device
> removal. This makes the tieoff descriptor lifetime much longer,
> avoiding repeating coherent buffer allocation on each open/close cycle.
> 
> Main benefit: we dissociate its lifetime from the main ring's lifetime.
> That way there is less work to be doing on resources (re)alloc. This
> currently happens on close/open, but will soon also happen on context
> swap operations (set_ringparam, change_mtu, set_channels, etc).
> 
> Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 75 
> +++++++++++++++++---------------
>  1 file changed, 41 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c 
> b/drivers/net/ethernet/cadence/macb_main.c
> index 8b52122bc134..951a7f080225 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c

> [...]

>  static void macb_init_rings(struct macb *bp)
> @@ -2832,8 +2801,6 @@ static void macb_init_rings(struct macb *bp)
>  	bp->queues[0].tx_head = 0;
>  	bp->queues[0].tx_tail = 0;
>  	desc->ctrl |= MACB_BIT(TX_WRAP);
> -
> -	macb_init_tieoff(bp);
>  }
> 
>  static void macb_reset_hw(struct macb *bp)
> @@ -5518,6 +5485,38 @@ static int eyeq5_init(struct platform_device 
> *pdev)
>  	return ret;
>  }
> 
> +static int macb_alloc_tieoff(struct macb *bp)
> +{
> +	/* Tieoff is a workaround in case HW cannot disable queues, for PM. 
> */
> +	if (bp->caps & MACB_CAPS_QUEUE_DISABLE)
> +		return 0;

Before, the tieoff was allocated in macb_alloc(), which the at91ether 
path
never called. Now it's allocated from macb_probe() for all variants, 
gated only
on MACB_CAPS_QUEUE_DISABLE, so EMAC gets a coherent descriptor it never 
uses.

Add MACB_CAPS_MACB_IS_EMAC to the if statement?

> [...]

Thanks
Nicolai