Re: [PATCH net 12/12] net: systemport: Complete resource teardown even on DMA disable timeout

[netdev-bot+sashiko@kernel.org]

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issue(s) to consider.

Critical: 0 · High: 1 · Medium: 1 (1) · Low: 0

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- [High] bcm_sysport_stop() now unmaps and frees the RX/TX DMA buffers
  even when the DMA engines are known to be still running.
- [Medium] The unconditional teardown path now reaches
  clk_disable_unprepare(priv->clk)…

Pre-existing issues:
- [Medium] The same early-return-on-DMA-disable-timeout pattern remains
  in bcm_sysport_suspend(): 'ret = rdma_enable_set(priv, 0); if (ret) {…

--

net: systemport: Complete resource teardown even on DMA disable timeout

bcm_sysport_stop() used to return early when tdma_enable_set() or
rdma_enable_set() timed out, which left the rings, interrupts, PHY and
clock in place because ndo_stop() return values are ignored. The patch
turns both early returns into plain error prints so the rest of the
teardown always runs.

A few questions on the new flow.

> diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c b/drivers/net/ethernet/broadcom/bcmsysport.c
> index e5bb7fa84fda5..2b064da4eb7c0 100644
> --- a/drivers/net/ethernet/broadcom/bcmsysport.c
> +++ b/drivers/net/ethernet/broadcom/bcmsysport.c
> @@ -2088,19 +2088,15 @@ static int bcm_sysport_stop(struct net_device *dev)
>  	umac_enable_set(priv, CMD_RX_EN, 0);
>  
>  	ret = tdma_enable_set(priv, 0);
> -	if (ret) {
> +	if (ret)
>  		netdev_err(dev, "timeout disabling TDMA\n");
> -		return ret;
> -	}
>  
>  	/* Wait for a maximum packet size to be drained */
>  	usleep_range(2000, 3000);
>  
>  	ret = rdma_enable_set(priv, 0);
> -	if (ret) {
> +	if (ret)
>  		netdev_err(dev, "timeout disabling RDMA\n");
> -		return ret;
> -	}

[Severity: High]
Can the device still DMA into the freed RX buffers here?

rdma_enable_set() only returns -ETIMEDOUT after polling RDMA_STATUS for
roughly a second without ever seeing RDMA_DISABLED, so the error return is
evidence that the engine has not quiesced. With the return gone,
bcm_sysport_stop() continues into:

	/* Free RX/TX rings SW structures */
	for (i = 0; i < dev->num_tx_queues; i++)
		bcm_sysport_fini_tx_ring(priv, i);
	bcm_sysport_fini_rx_ring(priv);

and bcm_sysport_fini_rx_ring() only warns about exactly this state before
releasing everything:

	/* Caller should ensure RDMA is disabled */
	reg = rdma_readl(priv, RDMA_STATUS);
	if (!(reg & RDMA_DISABLED))
		netdev_warn(priv->netdev, "RDMA not stopped!\n");

	if (!priv->rx_cbs)
		return;

	for (i = 0; i < priv->num_rx_bds; i++) {
		cb = &priv->rx_cbs[i];
		if (dma_unmap_addr(cb, dma_addr))
			dma_unmap_single(&priv->pdev->dev,
					 dma_unmap_addr(cb, dma_addr),
					 RX_BUF_LENGTH, DMA_FROM_DEVICE);
		bcm_sysport_free_cb(cb);
	}

	kfree(priv->rx_cbs);

bcm_sysport_fini_tx_ring() has the same "TDMA not stopped!" warning followed
by bcm_sysport_tx_clean() and kfree(ring->cbs).

umac_enable_set(priv, CMD_RX_EN, 0) stops the UniMAC, not the RDMA/TDMA
descriptor engines, and bcm_sysport_stop() does no TOPCTRL flush and no
block reset, unlike bcm_sysport_suspend() which writes RX_FLUSH/TX_FLUSH.
Would it be better to force the block quiescent on the timeout path first,
for example via topctrl_flush() and/or a block reset, before unmapping and
freeing the buffers? Alternatively, release the IRQs, PHY and clock while
keeping the DMA-mapped buffers owned by the driver, so the engine cannot
write into memory that has been returned to the allocator.

>  
>  	/* Disable UniMAC TX */
>  	umac_enable_set(priv, CMD_TX_EN, 0);

[Severity: Medium]
The commit message says "If the interface was subsequently brought up again,
request_irq() and PHY connection would fail or leak", which suggests the
interface is usable again after the fix. Does the re-open path actually
resynchronize the engines?

bcm_sysport_stop() now reaches clk_disable_unprepare(priv->clk) with
RDMA_EN/TDMA_EN never acknowledged as cleared, and no state is recorded to
say the DMA was stuck. On the next open, umac_reset() returns immediately
for priv->is_lite and otherwise only pulses CMD_SW_RESET, and
topctrl_flush() only pulses RX_FLUSH/TX_FLUSH; neither clears RDMA_EN or
TDMA_EN. bcm_sysport_init_rx_ring() then does:

	/* Initialize HW, ensure RDMA is disabled */
	reg = rdma_readl(priv, RDMA_STATUS);
	if (!(reg & RDMA_DISABLED))
		rdma_enable_set(priv, 0);

	rdma_writel(priv, 0, RDMA_WRITE_PTR_LO);
	rdma_writel(priv, 0, RDMA_WRITE_PTR_HI);
	rdma_writel(priv, 0, RDMA_PROD_INDEX);
	rdma_writel(priv, 0, RDMA_CONS_INDEX);

The rdma_enable_set() result is ignored and the pointer registers are zeroed
along with priv->rx_c_index and priv->rx_read_ptr, so if the engine is still
live its write pointer keeps advancing from the old position and the
software bookkeeping diverges from the hardware ring.
bcm_sysport_init_tx_ring() never samples TDMA_STATUS before rewriting
TDMA_DESC_RING_HEAD_TAIL_PTR/COUNT/PROD_CONS_INDEX, and bcm_sysport_open()
follows with:

	/* Initialize linked-list */
	tdma_writel(priv, TDMA_LL_RAM_INIT_BUSY, TDMA_STATUS);

Also, the later rdma_enable_set(priv, 1)/tdma_enable_set(priv, 1) in open()
return 0 immediately when the engine is already enabled, so open() reports
success on stale hardware state. Would recording a "DMA stuck" condition in
stop() and forcing a block reset on the next open make the re-open claim in
the commit message hold?

[Severity: Medium]
This is a pre-existing issue and not introduced by this patch, but should
bcm_sysport_suspend() be converted the same way for consistency? It still
has both early returns:

	ret = rdma_enable_set(priv, 0);
	if (ret) {
		netdev_err(dev, "RDMA timeout!\n");
		return ret;
	}
	...
	ret = tdma_enable_set(priv, 0);
	if (ret) {
		netdev_err(dev, "TDMA timeout!\n");
		return ret;
	}

Both return before bcm_sysport_fini_tx_ring()/bcm_sysport_fini_rx_ring() and
before clk_disable_unprepare(priv->clk), while netif_device_detach(),
bcm_sysport_netif_stop() and phy_suspend() have already run and are not
undone. On a DMA timeout the suspend is aborted with the interface detached
(so netif_device_present() is false and a later open returns -ENODEV), the
PHY suspended, the ring cb arrays and their mapped SKBs still allocated, and
a clk prepare/enable reference still held.

After this patch the driver handles the same hardware failure in two
different ways, and the suspend path additionally flushes RX via
topctrl_writel(RX_FLUSH, RX_FLUSH_CNTL) and disables RDMA before TDMA,
which stop() does not. Is the divergence intentional?

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260921231305.394773-1-florian.fainelli%40broadcom.com