linux-kernel - Re: [PATCH NET 3/3] net: hns: add configuration constraints for 1000M half

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Date:   Sat, 25 Aug 2018 09:21:55 +0800
From:   "lipeng (Y)" <lipeng321@...wei.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
        <yisen.zhuang@...wei.com>, <salil.mehta@...wei.com>
Subject: Re: [PATCH NET 3/3] net: hns: add configuration constraints for 1000M
 half



On 2018/8/24 21:28, Andrew Lunn wrote:
> On Fri, Aug 24, 2018 at 02:39:36PM +0800, lipeng (Y) wrote:
>>
>> On 2018/8/24 11:41, Andrew Lunn wrote:
>>> On Fri, Aug 24, 2018 at 11:42:23AM +0800, Peng Li wrote:
>>>> Hisilicon hip05 and hip06 board network card do not support
>>>> 1000M half configuration. Driver can not config gmac as
>>>> 1000M half.
>>>>
>>>> Signed-off-by: Peng Li <lipeng321@...wei.com>
>>> Hi Peng
>>>
>>> Does the driver remove SUPPORTED_1000baseT_Half from
>>> phydev->supported?  If you do that, the PHY should never negotiate
>>> this speed.
>>>
>>>     Andrew
>> Hi, Andrew,
>>
>> The driver has removed SUPPORTED_1000baseT_Half from
>>
>> phydev->supported.
>>
>> the code is :
>> #define MAC_GMAC_SUPPORTED \
>> 	(SUPPORTED_10baseT_Half \
>> 	| SUPPORTED_10baseT_Full \
>> 	| SUPPORTED_100baseT_Half \
>> 	| SUPPORTED_100baseT_Full \
>> 	| SUPPORTED_Autoneg)
>>   h->if_support = MAC_GMAC_SUPPORTED;
>>   h->if_support |= SUPPORTED_1000baseT_Full;
>> phydev->supported &= h->if_support;
>>
>> As gmac do not support 1000M half, we add this patch to
>> make sure that no users can set 1000M half in any case.
> Well, not quite. What this patch does is protect the hardware when it
> is asked to change to an unsupported mode. This patch has nothing to
> do with user APIs.
>
> The user API for setting link modes is hns_nic_set_link_ksettings().
>
> What you do have is
>
>                  if (speed == SPEED_1000 && cmd->base.duplex == DUPLEX_HALF)
>                          return -EINVAL;
>
> which should stop somebody setting up a fixed speed link at 1000Half.
>
> But you don't do anything with cmd->link_modes.advertising. However,
> when you call phy_ethtool_ksettings_set(), it gets AND'ed with
> phydev->supported, which you have already removed 1000Half from.
>
> So is this a patch for a theoretical problem? Or have you seen it
> happen? If it did happen, how did the user configure it to cause this
> problem? That user API needs to prevent it.
>
> 	 Andrew
Hi,  Andrew,

HW  do not support 1000M half, and the driver has done the 2 things:
1, remove SUPPORTED_1000baseT_Half from phydev->supported.
2,   add the protect in  hns_nic_set_link_ksettings().

This patch is a  theoretical protect, and the problem does not really  
happen.

I think you really get the point, do you think we need this patch?

Thanks
> .
>