netdev - Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

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Date:   Mon, 24 Aug 2020 08:10:36 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     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>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH v3 5/8] net: dsa: hellcreek: Add TAPRIO offloading support

On Sat Aug 22 2020, Vladimir Oltean wrote:
> Hi Kurt,
>
> On Thu, Aug 20, 2020 at 10:11:15AM +0200, Kurt Kanzenbach wrote:
>> The switch has support for the 802.1Qbv Time Aware Shaper (TAS). Traffic
>> schedules may be configured individually on each front port. Each port has eight
>> egress queues. The traffic is mapped to a traffic class respectively via the PCP
>> field of a VLAN tagged frame.
>> 
>> The TAPRIO Qdisc already implements that. Therefore, this interface can simply
>> be reused. Add .port_setup_tc() accordingly.
>> 
>> The activation of a schedule on a port is split into two parts:
>> 
>>  * Programming the necessary gate control list (GCL)
>>  * Setup hrtimer for starting the schedule
>> 
>> The hardware supports starting a schedule up to eight seconds in the future. The
>> TAPRIO interface provides an absolute base time. Therefore, hrtimers are
>> leveraged.
>> 
>> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
>> ---
>>  drivers/net/dsa/hirschmann/hellcreek.c | 294 +++++++++++++++++++++++++
>>  drivers/net/dsa/hirschmann/hellcreek.h |  21 ++
>>  2 files changed, 315 insertions(+)
>> 
>> diff --git a/drivers/net/dsa/hirschmann/hellcreek.c b/drivers/net/dsa/hirschmann/hellcreek.c
>> index 745ca60342b4..e5b54f42c635 100644
>> --- a/drivers/net/dsa/hirschmann/hellcreek.c
>> +++ b/drivers/net/dsa/hirschmann/hellcreek.c
>> @@ -22,7 +22,9 @@
>>  #include <linux/spinlock.h>
>>  #include <linux/delay.h>
>>  #include <linux/ktime.h>
>> +#include <linux/time.h>
>>  #include <net/dsa.h>
>> +#include <net/pkt_sched.h>
>>  
>>  #include "hellcreek.h"
>>  #include "hellcreek_ptp.h"
>> @@ -153,6 +155,15 @@ static void hellcreek_select_vlan(struct hellcreek *hellcreek, int vid,
>>  	hellcreek_write(hellcreek, val, HR_VIDCFG);
>>  }
>>  
>> +static void hellcreek_select_tgd(struct hellcreek *hellcreek, int port)
>> +{
>> +	u16 val = 0;
>> +
>> +	val |= port << TR_TGDSEL_TDGSEL_SHIFT;
>> +
>> +	hellcreek_write(hellcreek, val, TR_TGDSEL);
>> +}
>> +
>>  static int hellcreek_wait_until_ready(struct hellcreek *hellcreek)
>>  {
>>  	u16 val;
>> @@ -958,6 +969,24 @@ static void __hellcreek_setup_tc_identity_mapping(struct hellcreek *hellcreek)
>>  	}
>>  }
>>  
>> +static void hellcreek_setup_tc_mapping(struct hellcreek *hellcreek,
>> +				       struct net_device *netdev)
>> +{
>> +	int i, j;
>> +
>> +	/* Setup mapping between traffic classes and port queues. */
>> +	for (i = 0; i < netdev_get_num_tc(netdev); ++i) {
>> +		for (j = 0; j < netdev->tc_to_txq[i].count; ++j) {
>> +			const int queue = j + netdev->tc_to_txq[i].offset;
>> +
>> +			hellcreek_select_prio(hellcreek, i);
>> +			hellcreek_write(hellcreek,
>> +					queue << HR_PRTCCFG_PCP_TC_MAP_SHIFT,
>> +					HR_PRTCCFG);
>> +		}
>> +	}
>> +}
>
> What other driver have you seen that does this?
>

Probably none.

With TAPRIO traffic classes and the mapping to queues can be
configured. The switch can also map traffic classes. That sounded like a
good match to me.

Thanks,
Kurt

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