linux-kernel - Re: [PATCH net-next v1 3/5] net: stmmac: support fp parameter of tc-taprio

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Message-ID: <20240801231625.uqa4gq7vokp63dfp@skbuf>
Date: Fri, 2 Aug 2024 02:16:25 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: Furong Xu <0x1207@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Joao Pinto <jpinto@...opsys.com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	xfr@...look.com, rock.xu@....com
Subject: Re: [PATCH net-next v1 3/5] net: stmmac: support fp parameter of
 tc-taprio

On Wed, Jul 31, 2024 at 06:43:14PM +0800, Furong Xu wrote:
> tc-taprio can select whether traffic classes are express or preemptible.
> 
> After some traffic tests, MAC merge layer statistics are all good.
> 
> Local device:
> ethtool --include-statistics --json --show-mm eth1
> [ {
>         "ifname": "eth1",
>         "pmac-enabled": true,
>         "tx-enabled": true,
>         "tx-active": true,
>         "tx-min-frag-size": 60,
>         "rx-min-frag-size": 60,
>         "verify-enabled": true,
>         "verify-time": 100,
>         "max-verify-time": 128,
>         "verify-status": "SUCCEEDED",
>         "statistics": {
>             "MACMergeFrameAssErrorCount": 0,
>             "MACMergeFrameSmdErrorCount": 0,
>             "MACMergeFrameAssOkCount": 0,
>             "MACMergeFragCountRx": 0,
>             "MACMergeFragCountTx": 1398,
>             "MACMergeHoldCount": 15783
>         }
>     } ]
> 
> Remote device:
> ethtool --include-statistics --json --show-mm eth1
> [ {
>         "ifname": "eth1",
>         "pmac-enabled": true,
>         "tx-enabled": true,
>         "tx-active": true,
>         "tx-min-frag-size": 60,
>         "rx-min-frag-size": 60,
>         "verify-enabled": true,
>         "verify-time": 100,
>         "max-verify-time": 128,
>         "verify-status": "SUCCEEDED",
>         "statistics": {
>             "MACMergeFrameAssErrorCount": 0,
>             "MACMergeFrameSmdErrorCount": 0,
>             "MACMergeFrameAssOkCount": 1388,
>             "MACMergeFragCountRx": 1398,
>             "MACMergeFragCountTx": 0,
>             "MACMergeHoldCount": 0
>         }
>     } ]
> 
> Tested on DWMAC CORE 5.10a
> 
> Signed-off-by: Furong Xu <0x1207@...il.com>
> ---
>  .../net/ethernet/stmicro/stmmac/stmmac_tc.c   | 34 ++-----------------
>  1 file changed, 3 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> index 494fe2f68300..eeb5eb453b98 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c
> @@ -943,7 +943,6 @@ static int tc_taprio_configure(struct stmmac_priv *priv,
>  	u32 size, wid = priv->dma_cap.estwid, dep = priv->dma_cap.estdep;
>  	struct timespec64 time, current_time, qopt_time;
>  	ktime_t current_time_ns;
> -	bool fpe = false;
>  	int i, ret = 0;
>  	u64 ctr;
>  
> @@ -1028,16 +1027,6 @@ static int tc_taprio_configure(struct stmmac_priv *priv,
>  
>  		switch (qopt->entries[i].command) {
>  		case TC_TAPRIO_CMD_SET_GATES:
> -			if (fpe)
> -				return -EINVAL;
> -			break;
> -		case TC_TAPRIO_CMD_SET_AND_HOLD:
> -			gates |= BIT(0);
> -			fpe = true;
> -			break;
> -		case TC_TAPRIO_CMD_SET_AND_RELEASE:
> -			gates &= ~BIT(0);
> -			fpe = true;

I don't think these can go.

In the DWMAC5 manual, I see:
"To enable the support of hold and release operations, the format of the
GCL is slightly changed while configuring and enabling the FPE. The first Queue (Q0) is always programmed to carry preemption
traffic and therefore it is always Open. The bit corresponding to Q0 is renamed as Release/Hold MAC control. The TX Queues
whose packets are preemptable are indicated by setting the PEC field of the MTL_FPE_CTRL_STS register. The GCL bit of the
corresponding Queue are ignored and considered as always "Open". So, even if the software writes a "0" ("C"), it is ignored for
such queues."

It's relatively clear to me that this is what the "gates" variable is
doing here - it's modulating when preemptible traffic begins to be
"held", and when it is "released".

Now, the "fpe" variable - that can definitely go.

>  			break;
>  		default:
>  			return -EOPNOTSUPP;

Also, this is more general advice. If TC_TAPRIO_CMD_SET_AND_HOLD and
TC_TAPRIO_CMD_SET_AND_RELEASE used to work as UAPI input into this
driver, you don't want to break that now by letting those fall into the
default -EOPNOTSUPP case. What worked must continue to work... somehow.

> @@ -1068,16 +1057,11 @@ static int tc_taprio_configure(struct stmmac_priv *priv,
>  
>  	tc_taprio_map_maxsdu_txq(priv, qopt);
>  
> -	if (fpe && !priv->dma_cap.fpesel) {
> +	if (qopt->mqprio.preemptible_tcs && !priv->dma_cap.fpesel) {
>  		mutex_unlock(&priv->est_lock);
>  		return -EOPNOTSUPP;
>  	}
>  
> -	/* Actual FPE register configuration will be done after FPE handshake
> -	 * is success.
> -	 */
> -	priv->plat->fpe_cfg->enable = fpe;
> -
>  	ret = stmmac_est_configure(priv, priv, priv->est,
>  				   priv->plat->clk_ptp_rate);
>  	mutex_unlock(&priv->est_lock);