Re: [net,PATCH v1] net: ks8851: Fix receiver error in 100BASE-TX mode following software power-down

[Marek Vasut <marex@nabladev.com>]

On 9/4/26 2:37 AM, Jakub Kicinski wrote:
> This is an AI-generated review of your patch.

Sigh, a wall of generated text.

> The human sending this
> email has considered the AI review valid, or at least plausible.
> ---
> net: ks8851: Fix receiver error in 100BASE-TX mode following software power-down
> 
> Per the KSZ8851 errata (DS80000716D, Module 3), a software power-down
> followed by a power-on can leave the receiver circuit non-functional. This
> patch implements the documented workaround by dropping both transitions into
> PMECR_PM_SOFTDOWN, in ks8851_write_mac_addr() and ks8851_net_stop().
> 
> Link: https://ww1.microchip.com/downloads/en/DeviceDoc/80000716D.pdf
> 
>> diff --git a/drivers/net/ethernet/micrel/ks8851_common.c b/drivers/net/ethernet/micrel/ks8851_common.c
>> index 4afbb40bc0e4a..cd8dfca22720b 100644
>> --- a/drivers/net/ethernet/micrel/ks8851_common.c
>> +++ b/drivers/net/ethernet/micrel/ks8851_common.c
>> @@ -143,9 +143,6 @@ static int ks8851_write_mac_addr(struct net_device *dev)
>>   		ks8851_wrreg16(ks, KS_MAR(i), val);
>>   	}
>>   
>> -	if (!netif_running(dev))
>> -		ks8851_set_powermode(ks, PMECR_PM_SOFTDOWN);
>> -
>>   	ks8851_unlock(ks);
>>   
>>   	return 0;
> 
> [Severity: Low]
> This isn't a bug

Aha ...

>, but should the two comments describing the software
> power-down state be updated in the same patch?
> 
> After this hunk, ks8851_write_mac_addr() still carries this comment above
> its remaining ks8851_set_powermode() call:
> 
> 	/*
> 	 * Wake up chip in case it was powered off when stopped; otherwise,
> 	 * the first write to the MAC address does not take effect.
> 	 */
> 	ks8851_set_powermode(ks, PMECR_PM_NORMAL);
> 
> Nothing in the driver can put the chip into software power-down anymore, so
> the "in case it was powered off when stopped" precondition can no longer
> occur. A grep of the tree confirms PMECR_PM_SOFTDOWN has no users left,
> only its definition in ks8851.h, and the two remaining
> ks8851_set_powermode() call sites in ks8851_write_mac_addr() and
> ks8851_net_start() both write PMECR_PM_NORMAL.

The driver obviously does not exist in a vacuum and prior stage before 
Linux could have easily left the MAC in whatever powered down state. 
This is bogus feedback.

> Since the commit message uses that very call site as the argument that
> dropping the power-down here is safe, would it help to note in the comment
> that the PM_NORMAL write is kept deliberately (e.g. referencing the errata),
> so a later cleanup does not remove it or reintroduce the SOFTDOWN
> transition?
> 
>> @@ -506,8 +503,6 @@ static int ks8851_net_stop(struct net_device *dev)
>>   	/* shutdown TX process */
>>   	ks8851_wrreg16(ks, KS_TXCR, 0x0000);
>>   
>> -	/* set powermode to soft power down to save power */
>> -	ks8851_set_powermode(ks, PMECR_PM_SOFTDOWN);
>>   	ks8851_unlock(ks);
> 
> [Severity: Low]
> Related to the above: the kernel-doc for ks8851_net_stop() just above this
> function still promises the low power transition that is being removed here:
> 
> 	/**
> 	 * ks8851_net_stop - close network device
> 	 * @dev: The device being closed.
> 	 *
> 	 * Called to close down a network device which has been active. Cancel any
> 	 * work, shutdown the RX and TX process and then place the chip into a low
> 	 * power state whilst it is not being used.
> 	 */
> 
> The post-patch body only masks IER/ISR, zeroes RXCR1/TXCR, drains ks->txq
> and calls free_irq(), with no PMECR access left. Should that last sentence
> be dropped or reworded to mention the errata, so readers of
> ks8851_suspend()->ks8851_net_stop() are not told a low power transition
> happens?

What exactly should I adjust in V2 ?