netdev - Re: [PATCH net-next v5 2/2] net: phy: broadcom: Add PTP support for some Broadcom PHYs.

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Date:   Sun, 22 May 2022 19:49:20 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     netdev@...r.kernel.org, andrew@...n.ch, hkallweit1@...il.com,
        linux@...linux.org.uk, bcm-kernel-feedback-list@...adcom.com,
        kernel-team@...com, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, edumazet@...gle.com
Subject: Re: [PATCH net-next v5 2/2] net: phy: broadcom: Add PTP support for
 some Broadcom PHYs.



On 5/20/2022 7:04 PM, Jonathan Lemon wrote:
> On Fri, May 20, 2022 at 10:24:25AM -0700, Florian Fainelli wrote:
>>
>>
>> On 5/18/2022 3:39 PM, Jonathan Lemon wrote:
>>> This adds PTP support for BCM54210E Broadcom PHYs, in particular,
>>> the BCM54213PE, as used in the Rasperry PI CM4.  It has only been
>>> tested on that hardware.
>>>
>>> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
>>> ---
>> [snip]
>>
>> Looks good to me, just one question below:
>>
>>> +static void bcm_ptp_init(struct bcm_ptp_private *priv)
>>> +{
>>> +	priv->nse_ctrl = NSE_GMODE_EN;
>>> +
>>> +	mutex_init(&priv->mutex);
>>> +	skb_queue_head_init(&priv->tx_queue);
>>> +
>>> +	priv->mii_ts.rxtstamp = bcm_ptp_rxtstamp;
>>> +	priv->mii_ts.txtstamp = bcm_ptp_txtstamp;
>>> +	priv->mii_ts.hwtstamp = bcm_ptp_hwtstamp;
>>> +	priv->mii_ts.ts_info = bcm_ptp_ts_info;
>>> +
>>> +	priv->phydev->mii_ts = &priv->mii_ts;
>>> +
>>> +	INIT_DELAYED_WORK(&priv->out_work, bcm_ptp_fsync_work);
>>
>> Do we need to make sure that we cancel the workqueue in an bcm_ptp_exit()
>> function?
>>
>> I would imagine that the Ethernet MAC attached to that PHY device having
>> stopped its receiver and transmitter should ensure no more packets coming in
>> or out, however since this is a delayed/asynchronous work, do not we need to
>> protect against use after free?
> 
> The workqueue is just mamually creatimg a 1PPS pulse on the SYNC_OUT
> pin, no packet activity.  Arguably, the .suspend hook could stop all work,
> but that seems out of scope here? (and this phy does not suspend/resume)

The BCM54210E entry does have a suspend/resume entry so it seems to me 
that we do need to cancel the workqueue as the PHY library will not do 
that on our behalf. What I imagine could happen is that this workqueue 
generates spurious MDIO accesses *after* both the PHY and the bus have 
been suspended (and their driver's clock possibly gated already).
-- 
Florian