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Subject: Re: [PATCH] net: macb: fix NULL dereference due to no pcs_config
 method
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
CC:     Parshuram Thombare <pthombar@cadence.com>, <kuba@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>, <netdev@vger.kernel.org>,
        <Claudiu.Beznea@microchip.com>, <Santiago.Esteban@microchip.com>,
        <andrew@lunn.ch>, <davem@davemloft.net>,
        <linux-kernel@vger.kernel.org>, <harini.katakam@xilinx.com>,
        <michal.simek@xilinx.com>
References: <1604587039-5646-1-git-send-email-pthombar@cadence.com>
 <6873cf12-456b-c121-037b-d2c5a6138cb3@microchip.com>
 <20201105154856.GN1551@shell.armlinux.org.uk>
From:   Nicolas Ferre <nicolas.ferre@microchip.com>
Organization: microchip
Message-ID: <ef62fed6-3701-314f-9712-ef53142095a8@microchip.com>
Date:   Thu, 5 Nov 2020 17:38:08 +0100
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On 05/11/2020 at 16:48, Russell King - ARM Linux admin wrote:
> On Thu, Nov 05, 2020 at 04:22:18PM +0100, Nicolas Ferre wrote:
>> On 05/11/2020 at 15:37, Parshuram Thombare wrote:
>>> This patch fixes NULL pointer dereference due to NULL pcs_config
>>> in pcs_ops.
>>>
>>> Fixes: e4e143e26ce8 ("net: macb: add support for high speed interface")
>>
>> What is this tag? In linux-next? As patch is not yet in Linus' tree, you
>> cannot refer to it like this.
>>
>>> Reported-by: Nicolas Ferre <Nicolas.Ferre@microchip.com>
>>> Link: https://lkml.org/lkml/2020/11/4/482
>>
>> You might need to change this to a "lore" link:
>> https://lore.kernel.org/netdev/2db854c7-9ffb-328a-f346-f68982723d29@microchip.com/
>>
>>> Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
>>
>> This fix looks a bit weird to me. What about proposing a patch to Russell
>> like the chunk that you already identified in function
>> phylink_major_config()?
> 
> No thanks. macb is currently the only case where a stub implementation
> for pcs_config() is required, which only occurs because the only
> appropriate protocol supported there is SGMII and not 1000base-X as
> well.

Got it.

>>> ---
>>>    drivers/net/ethernet/cadence/macb_main.c | 17 +++++++++++++++--
>>>    1 file changed, 15 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
>>> index b7bc160..130a5af 100644
>>> --- a/drivers/net/ethernet/cadence/macb_main.c
>>> +++ b/drivers/net/ethernet/cadence/macb_main.c
>>> @@ -633,6 +633,15 @@ static void macb_pcs_an_restart(struct phylink_pcs *pcs)
>>>           /* Not supported */
>>>    }
>>>
>>> +static int macb_pcs_config(struct phylink_pcs *pcs,
>>> +                          unsigned int mode,
>>> +                          phy_interface_t interface,
>>> +                          const unsigned long *advertising,
>>> +                          bool permit_pause_to_mac)
>>> +{
>>> +       return 0;
>>> +}
>>
>> Russell, is the requirement for this void function intended?
> 
> In response to v3 of the patch on 21st October, I said, and I quote:
> 
>    I think all that needs to happen is a pcs_ops for the non-10GBASE-R
>    mode which moves macb_mac_pcs_get_state() and macb_mac_an_restart()
>    to it, and implements a stub pcs_config(). So it should be simple
>    to do.
> 
> Obviously, my advice was not followed, I didn't spot the lack of it
> in v4 (sorry), and the result is the NULL pointer oops.

Fair enough. So Parshuram I'll add my ack tag when you re-send your 
patch with little issues fixed.

Thanks for your help Russell.

Best regards,
   Nicolas
-- 
Nicolas Ferre