linux-kernel - Re: [PATCH net] ravb: Fix bit fields checking in ravb_hwtstamp

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Date:   Sat, 17 Oct 2020 22:49:23 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...il.com>
To:     Andrew Gabbasov <andrew_gabbasov@...tor.com>
Cc:     linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>, geert+renesas@...der.be,
        Julia Lawall <julia.lawall@...ia.fr>,
        "Behme, Dirk - Bosch" <dirk.behme@...bosch.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>
Subject: Re: [PATCH net] ravb: Fix bit fields checking in ravb_hwtstamp_get()

Hello!

On 10/1/20 10:13 AM, Andrew Gabbasov wrote:

   The patch was set to the "Changes Requested" state -- most probably because of this
mail. Though unintentionally, it served to throttle actions on this patch. I did only
remember about this patch yesterday... :-)

[...]
>> In the function ravb_hwtstamp_get() in ravb_main.c with the existing
> values
>> for RAVB_RXTSTAMP_TYPE_V2_L2_EVENT (0x2) and RAVB_RXTSTAMP_TYPE_ALL
>> (0x6)
>>
>> if (priv->tstamp_rx_ctrl & RAVB_RXTSTAMP_TYPE_V2_L2_EVENT)
>> 	config.rx_filter = HWTSTAMP_FILTER_PTP_V2_L2_EVENT;
>> else if (priv->tstamp_rx_ctrl & RAVB_RXTSTAMP_TYPE_ALL)
>> 	config.rx_filter = HWTSTAMP_FILTER_ALL;
>>
>> if the test on RAVB_RXTSTAMP_TYPE_ALL should be true, it will never be
>> reached.
>>
>> This issue can be verified with 'hwtstamp_config' testing program
>> (tools/testing/selftests/net/hwtstamp_config.c). Setting filter type to
> ALL
>> and subsequent retrieving it gives incorrect value:
>>
>> $ hwtstamp_config eth0 OFF ALL
>> flags = 0
>> tx_type = OFF
>> rx_filter = ALL
>> $ hwtstamp_config eth0
>> flags = 0
>> tx_type = OFF
>> rx_filter = PTP_V2_L2_EVENT
>>
>> Correct this by converting if-else's to switch.
> 
> Earlier you proposed to fix this issue by changing the value
> of RAVB_RXTSTAMP_TYPE_ALL constant to 0x4.
> Unfortunately, simple changing of the constant value will not
> be enough, since the code in ravb_rx() (actually determining
> if timestamp is needed)
> 
> u32 get_ts = priv->tstamp_rx_ctrl & RAVB_RXTSTAMP_TYPE;
> [...]
> get_ts &= (q == RAVB_NC) ?
>                 RAVB_RXTSTAMP_TYPE_V2_L2_EVENT :
>                 ~RAVB_RXTSTAMP_TYPE_V2_L2_EVENT;
> 
> will work incorrectly and will need to be fixed too, making this
> piece of code more complicated.
> 
> So, it's probably easier and safer to keep the constant value and
> the code in ravb_rx() intact, and just fix the get ioctl code,
> where the issue is actually located.

   We have one more issue with the current driver: bit 2 of priv->tstamp_rx_ctrl
can only be set as a part of the ALL mask, not individually. I'm now thinking we
should set RAVB_RXTSTAMP_TYPE[_ALL] to 2 (and probably just drop the ALL mask)...

[...]

>> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
>> Reported-by: Julia Lawall <julia.lawall@...ia.fr>
>> Signed-off-by: Andrew Gabbasov <andrew_gabbasov@...tor.com>
>> ---
>>  drivers/net/ethernet/renesas/ravb_main.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c
>> b/drivers/net/ethernet/renesas/ravb_main.c
>> index df89d09b253e..c0610b2d3b14 100644
>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>> @@ -1802,12 +1802,16 @@ static int ravb_hwtstamp_get(struct net_device
>> *ndev, struct ifreq *req)
>>  	config.flags = 0;
>>  	config.tx_type = priv->tstamp_tx_ctrl ? HWTSTAMP_TX_ON :
>>  						HWTSTAMP_TX_OFF;
>> -	if (priv->tstamp_rx_ctrl & RAVB_RXTSTAMP_TYPE_V2_L2_EVENT)
>> +	switch (priv->tstamp_rx_ctrl & RAVB_RXTSTAMP_TYPE) {
>> +	case RAVB_RXTSTAMP_TYPE_V2_L2_EVENT:
>>  		config.rx_filter = HWTSTAMP_FILTER_PTP_V2_L2_EVENT;
>> -	else if (priv->tstamp_rx_ctrl & RAVB_RXTSTAMP_TYPE_ALL)
>> +		break;
>> +	case RAVB_RXTSTAMP_TYPE_ALL:
>>  		config.rx_filter = HWTSTAMP_FILTER_ALL;
>> -	else
>> +		break;
>> +	default:
>>  		config.rx_filter = HWTSTAMP_FILTER_NONE;

   Yeah, that's better. But do we really need am anonymous bit 2 that can't be
toggled other than via passing the ALL mask?

[...]

MBR, Sergei