[PATCH net v2] can: flexcan: fix synchronous external abort in flexcan_get_berr_counter()

When the interface is down, can_fill_info() still calls
flexcan_get_berr_counter() to fill the error counters for a netlink
dump. On some SoCs (e.g. i.MX8QXP) this can trigger a synchronous
external abort.

The root cause is platform-specific clocking. On i.MX8QXP the CAN
clocks are gated through the SCU LPCG and the whole subsystem shares
the IMX_SC_R_CAN_0 power domain. flexcan_runtime_resume() only calls
flexcan_clks_enable(); combined with the LPCG e10858 synchronization
erratum, there is a window where pm_runtime_resume_and_get() has
returned but the clock has not actually reached the module yet. The
immediate readl(&regs->ecr) in that window hits an un-clocked target
and faults with the external abort:

    Internal error: synchronous external abort: 0000000096000210 [#1] PREEMPT SMP
    pc : flexcan_read_le+0x0/0x18
    lr : flexcan_get_berr_counter+0x4c/0x8c
    Call trace:
     flexcan_read_le+0x0/0x18
     can_fill_info+0x1f8/0x434
     rtnl_fill_ifinfo+0x8fc/0xbb4
     rtnl_dump_ifinfo+0x364/0x448
     ...

This is the same class of problem that was already fixed for m_can:

  commit 91a55c72a821d ("can: m_can: m_can_get_berr_counter(): don't
  wake up controller if interface is down")

Fix this by returning early if the interface is not running.

Tested on i.MX8QXP: after the patch, `ip link show` no longer triggers
the abort.

Fixes: ec56acfef2af1 ("can: flexcan: flexcan_get_berr_counter(): switch on clocks before accessing ecr register")
Link: https://lore.kernel.org/netdev/20260915063511.3010642-1-chunyuzhiqiang@yinhe.ht/ (local)
Cc: stable@vger.kernel.org
Signed-off-by: ChunYuZhiQiang <redacted>
---
v1 -> v2:
  - Reword the commit message to drop the MDIS reasoning and describe
    the actual i.MX8QXP SCU/LPCG clocking window as the root cause.
  - Reference the m_can precedent (91a55c72a821d).
  - Add Fixes: tag pointing to ec56acfef2af1.
  - Add Link: to v1.

 drivers/net/can/flexcan/flexcan-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/can/flexcan/flexcan-core.c b/drivers/net/can/flexcan/flexcan-core.c
index 06d5d35fc1b5..b08779ee2a0a 100644
--- a/drivers/net/can/flexcan/flexcan-core.c
+++ b/drivers/net/can/flexcan/flexcan-core.c

@@ -765,6 +765,9 @@ static int flexcan_get_berr_counter(const struct net_device *dev,
 	const struct flexcan_priv *priv = netdev_priv(dev);
 	int err;
 
+	if (!netif_running(dev))
+		return 0;
+
 	err = pm_runtime_resume_and_get(priv->dev);
 	if (err < 0)
 		return err;

-- 
2.47.3