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Date:   Tue, 3 Dec 2019 12:42:04 -0500
From:   Murali Karicheri <m-karicheri2@...com>
To:     Po Liu <po.liu@....com>,
        "rmk+kernel@...linux.org.uk" <rmk+kernel@...linux.org.uk>,
        "linville@...driver.com" <linville@...driver.com>,
        "netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "vinicius.gomes@...el.com" <vinicius.gomes@...el.com>,
        "simon.horman@...ronome.com" <simon.horman@...ronome.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Roy Zang <roy.zang@....com>, Mingkai Hu <mingkai.hu@....com>,
        Jerry Huang <jerry.huang@....com>, Leo Li <leoyang.li@....com>
Subject: Re: [v1,ethtool] ethtool: add setting frame preemption of traffic
 classes

Hi Po Liu,

Thanks for working on this! Some suggestion below as we are working on
adding this support to Texas Instrument's CPSW driver on AM65x family
of SoCs as well. TRM for that is provided below for your reference.
Relevant section for IET (Frame pre-emption) is

12.2.1.4.6.6.1IET Configuration

http://www.ti.com/lit/ug/spruid7d/spruid7d.pdf

On 12/03/2019 11:27 AM, Ivan Khoronzhuk wrote:
> On Wed, Nov 27, 2019 at 09:58:52AM +0000, Po Liu wrote:
> 
> Hi Po Liu,
> 
>> IEEE Std 802.1Qbu standard defined the frame preemption of port
>> trffic classes. User can set a value to hardware. The value will
>> be translated to a binary, each bit represent a traffic class.
>> Bit "1" means preemptable traffic class. Bit "0" means express
>> traffic class.  MSB represent high number traffic class.
>>
>> ethtool -k devname
>>
>> This command would show if the tx-preemption feature is available.
>> If hareware set preemption feature. The property would be a fixed
>> value 'on' if hardware support the frame preemption. Feature would
>> show a fixed value 'off' if hardware don't support the frame preemption.
>>
>> ethtool devname
>>
>> This command would show include an item 'preemption'. A following
>> value '0' means all traffic classes are 'express'. A value none zero
>> means traffic classes preemption capabilities. The value will be
>> translated to a binary, each bit represent a traffic class. Bit '1'
>> means preemptable traffic class. Bit '0' means express traffic class.
>> MSB represent high number traffic class.
>>
>> ethtool -s devname preemption N
> 
> What about other potential parameters like MAC fragment size, mac hold?
> Shouldn't be it considered along with other FP parameters to provide 
> correct
> interface later?
> 
> Say, preemption, lets name it fp-mask or frame-preemption-mask.
> Then other potential setting can be similar and added later:
> 
> frame-preemption-mask
> frame-preemption-fragsize
> frame-preemption-machold
Need additional capabilities as described by Ivan above. Thanks Ivan!

So it would be better to use feature/sub-parameter format so that it can 
be extended as needed in the future.

For express/Preemptable mask setting it becomes

ethtool -s devname frame-preemption tc-mask  N

For setting min fragment size

ethtool -s devname frame-preemption min-fragsize 64

Also the device may be capable of doing Verify process to detect the
capability of neighbor device and show the status. So we should have a
way to show this status as well when user type

ethtool devname

We are working currently to add this feature to CPSW driver on AM65x
which will be upstream-ed soon. So want to have this done in an
way that we can extend it later.

Similarly for taprio, there are some parameters that user
might want to tune such as Max SDU size per tc class. I hope
we could use ethtool to set the same on a similar way.

Thanks

Murali

> ....
> 
> mac-hold it's rather flag, at least I've used it as priv-flag.
> so can or so
> 
> frame-preemption-flags
> 
>>
>> This command would set which traffic classes are frame preemptable.
>> The value will be translated to a binary, each bit represent a
>> traffic class. Bit '1' means preemptable traffic class. Bit '0'
>> means express traffic class. MSB represent high number traffic class.
>>
>> Signed-off-by: Po Liu <Po.Liu@....com>
>> ---
>> ethtool-copy.h |  6 +++++-
>> ethtool.8.in   |  8 ++++++++
>> ethtool.c      | 18 ++++++++++++++++++
>> 3 files changed, 31 insertions(+), 1 deletion(-)
>>
>> diff --git a/ethtool-copy.h b/ethtool-copy.h
>> index 9afd2e6..e04bdf3 100644
>> --- a/ethtool-copy.h
>> +++ b/ethtool-copy.h
>> @@ -1662,6 +1662,9 @@ static __inline__ int 
>> ethtool_validate_duplex(__u8 duplex)
>> #define AUTONEG_DISABLE        0x00
>> #define AUTONEG_ENABLE        0x01
>>
>> +/* Disable preemtion. */
>> +#define PREEMPTION_DISABLE    0x0
>> +
>> /* MDI or MDI-X status/control - if MDI/MDI_X/AUTO is set then
>>  * the driver is required to renegotiate link
>>  */
>> @@ -1878,7 +1881,8 @@ struct ethtool_link_settings {
>>     __s8    link_mode_masks_nwords;
>>     __u8    transceiver;
>>     __u8    reserved1[3];
>> -    __u32    reserved[7];
>> +    __u32    preemption;
>> +    __u32    reserved[6];
>>     __u32    link_mode_masks[0];
>>     /* layout of link_mode_masks fields:
>>      * __u32 map_supported[link_mode_masks_nwords];
>> diff --git a/ethtool.8.in b/ethtool.8.in
>> index 062695a..7d612b2 100644
>> --- a/ethtool.8.in
>> +++ b/ethtool.8.in
>> @@ -236,6 +236,7 @@ ethtool \- query or control network driver and 
>> hardware settings
>> .B2 autoneg on off
>> .BN advertise
>> .BN phyad
>> +.BN preemption
>> .B2 xcvr internal external
>> .RB [ wol \ \*(WO]
>> .RB [ sopass \ \*(MA]
>> @@ -703,6 +704,13 @@ lB    l    lB.
>> .BI phyad \ N
>> PHY address.
>> .TP
>> +.BI preemption \ N
>> +Set preemptable traffic classes by bits.
>> +.B A
>> +value will be translated to a binary, each bit represent a traffic 
>> class.
>> +Bit "1" means preemptable traffic class. Bit "0" means express 
>> traffic class.
>> +MSB represent high number traffic class.
>> +.TP
>> .A2 xcvr internal external
>> Selects transceiver type. Currently only internal and external can be
>> specified, in the future further types might be added.
>> diff --git a/ethtool.c b/ethtool.c
>> index acf183d..d5240f8 100644
>> --- a/ethtool.c
>> +++ b/ethtool.c
>> @@ -928,6 +928,12 @@ dump_link_usettings(const struct 
>> ethtool_link_usettings *link_usettings)
>>         }
>>     }
>>
>> +    if (link_usettings->base.preemption == PREEMPTION_DISABLE)
>> +        fprintf(stdout, "    Preemption: 0x0 (off)\n");
>> +    else
>> +        fprintf(stdout, "    Preemption: 0x%x\n",
>> +            link_usettings->base.preemption);
>> +
>>     return 0;
>> }
>>
>> @@ -2869,6 +2875,7 @@ static int do_sset(struct cmd_context *ctx)
>>     int port_wanted = -1;
>>     int mdix_wanted = -1;
>>     int autoneg_wanted = -1;
>> +    int preemption_wanted = -1;
>>     int phyad_wanted = -1;
>>     int xcvr_wanted = -1;
>>     u32 *full_advertising_wanted = NULL;
>> @@ -2957,6 +2964,12 @@ static int do_sset(struct cmd_context *ctx)
>>             } else {
>>                 exit_bad_args();
>>             }
>> +        } else if (!strcmp(argp[i], "preemption")) {
>> +            gset_changed = 1;
>> +            i += 1;
>> +            if (i >= argc)
>> +                exit_bad_args();
>> +            preemption_wanted = get_u32(argp[i], 16);
>>         } else if (!strcmp(argp[i], "advertise")) {
>>             gset_changed = 1;
>>             i += 1;
>> @@ -3094,6 +3107,9 @@ static int do_sset(struct cmd_context *ctx)
>>             }
>>             if (autoneg_wanted != -1)
>>                 link_usettings->base.autoneg = autoneg_wanted;
>> +            if (preemption_wanted != -1)
>> +                link_usettings->base.preemption
>> +                    = preemption_wanted;
>>             if (phyad_wanted != -1)
>>                 link_usettings->base.phy_address = phyad_wanted;
>>             if (xcvr_wanted != -1)
>> @@ -3186,6 +3202,8 @@ static int do_sset(struct cmd_context *ctx)
>>                 fprintf(stderr, "  not setting transceiver\n");
>>             if (mdix_wanted != -1)
>>                 fprintf(stderr, "  not setting mdix\n");
>> +            if (preemption_wanted != -1)
>> +                fprintf(stderr, "  not setting preemption\n");
>>         }
>>     }
>>
>> -- 
>> 2.17.1
>>
> 

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