netdev - Re: [PATCH v3 1/9] ptp: Add generic ptp v2 header parsing function

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Date:   Wed, 5 Aug 2020 00:34:47 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     Kurt Kanzenbach <kurt@...utronix.de>,
        Petr Machata <petrm@...lanox.com>,
        Richard Cochran <richardcochran@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Samuel Zou <zou_wei@...wei.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 1/9] ptp: Add generic ptp v2 header parsing function



On 05/08/2020 00:07, Russell King - ARM Linux admin wrote:
> On Tue, Aug 04, 2020 at 11:56:12PM +0300, Grygorii Strashko wrote:
>>
>>
>> On 31/07/2020 13:06, Kurt Kanzenbach wrote:
>>> On Thu Jul 30 2020, Petr Machata wrote:
>>>> Kurt Kanzenbach <kurt@...utronix.de> writes:
>>>>
>>>>> @@ -107,6 +107,37 @@ unsigned int ptp_classify_raw(const struct sk_buff *skb)
>>>>>    }
>>>>>    EXPORT_SYMBOL_GPL(ptp_classify_raw);
>>>>> +struct ptp_header *ptp_parse_header(struct sk_buff *skb, unsigned int type)
>>>>> +{
>>>>> +	u8 *data = skb_mac_header(skb);
>>>>> +	u8 *ptr = data;
>>>>
>>>> One of the "data" and "ptr" variables is superfluous.
>>>
>>> Yeah. Can be shortened to u8 *ptr = skb_mac_header(skb);
>>
>> Actually usage of skb_mac_header(skb) breaks CPTS RX time-stamping on
>> am571x platform PATCH 6.
>>
>> The CPSW RX timestamp requested after full packet put in SKB, but
>> before calling eth_type_trans().
>>
>> So, skb->data pints on Eth header, but skb_mac_header() return garbage.
>>
>> Below diff fixes it for me.
> 
> However, that's likely to break everyone else.
> 
> For example, anyone calling this from the mii_timestamper rxtstamp()
> method, the skb will have been classified with the MAC header pushed
> and restored, so skb->data points at the network header.
> 
> Your change means that ptp_parse_header() expects the MAC header to
> also be pushed.
> 
> Is it possible to adjust CPTS?
> 
> Looking at:
> drivers/net/ethernet/ti/cpsw.c... yes.
> drivers/net/ethernet/ti/cpsw_new.c... yes.
> drivers/net/ethernet/ti/netcp_core.c... unclear.
> 
> If not, maybe cpts should remain unconverted - I don't see any reason
> to provide a generic function for one user.
> 

Could it be an option to pass "u8 *ptr" instead of "const struct sk_buff *skb" as
input parameter to ptp_parse_header()?

-- 
Best regards,
grygorii