Re: [PATCH v5 RESEND net 0/3] net: enetc: safely reinitialize TX BD ring when it has unsent frames

[Simon Horman <horms@kernel.org>]

On Tue, Mar 24, 2026 at 02:21:18PM +0800, Wei Fang wrote:
> Currently the driver does not reset the producer index register (PIR) and
> consumer index register (CIR) when initializing a TX BD ring. The driver
> only reads the PIR and CIR and initializes the software indexes. If the
> TX BD ring is reinitialized when it still contains unsent frames, its PIR
> and CIR will not be equal after the reinitialization. However, the BDs
> between CIR and PIR have been freed and become invalid and this can lead
> to a hardware malfunction, causing the TX BD ring will not work properly.
> 
> Since the PIR and CIR are sofeware-configurable on ENETC v4. Therefore,
> the driver must reset them if they are not equal when reinitializing
> the TX BD ring.
> 
> However, resetting the PIR and CIR alone is insufficient, it cannot
> completely solve the problem. When a link-down event occurs while the TX
> BD ring is transmitting frames, subsequent reinitialization of the TX BD
> ring may cause it to malfunction. Because enetc4_pl_mac_link_down() only
> clears PMa_COMMAND_CONFIG[TX_EN] to disable MAC transmit data path. It
> doesn't set PORT[TXDIS] to 1 to flush the TX BD ring. Therefore, it is
> not safe to reinitialize the TX BD ring at this point.
> 
> To safely reinitialize the TX BD ring after a link-down event, we checked
> with the NETC IP team, a proper Ethernet MAC graceful stop is necessary.
> Therefore, add the Ethernet MAC graceful stop to the link-down event
> handler enetc4_pl_mac_link_down(). Note that this patch set is not
> applicable to ENETC v1 (LS1028A).
> 
> ---
> v5 link: https://lore.kernel.org/netdev/20260313094644.1132411-1-wei.fang@nxp.com/
> v5:
> 1. Add patch 3
> 2. Correct the typo in commit message of patch 1
> v4 link: https://lore.kernel.org/imx/20260312095415.669128-1-wei.fang@nxp.com/
> v4:
> Correct the offset of ENETC4_PSR
> v3 link: https://lore.kernel.org/imx/20260311084105.3982037-1-wei.fang@nxp.com/
> v3:
> 1. Split the v2 patch into two parts
> 2. Update the comments regarding PIR and CIR in enetc_setup_txbdr()
> 3. Use read_poll_timeout() instead of the while loop
> v2 link: https://lore.kernel.org/imx/20260309030412.2716984-1-wei.fang@nxp.com/
> v2:
> 1. Remove unused register macros (ENETC_SISR and SISR_TX_BUSY)
> 2. Remove spurious semicolon from enetc4_mac_wait_rx_empty()

For the series,

Reviewed-by: Simon Horman <horms@kernel.org>