Subject: Re: [PATCH net-next 08/13] net: dsa: hellcreek: deny tc-taprio changes to per-tc max SDU

From: Kurt Kanzenbach <[email-masked]>
Date: Thu, 22 Sep 2022 10:10:13 +0200

On Wed Sep 21 2022, Vladimir Oltean wrote:
> On Wed, Sep 21, 2022 at 05:12:06PM +0300, Vladimir Oltean wrote:
>> On Wed, Sep 21, 2022 at 01:46:22PM +0200, Kurt Kanzenbach wrote:
>> > >> So, configured to 128 and 132 bytes (including VLAN Ethernet header) is
>> > >> the maximum frame size which passes through.
>> > >
>> > > Frame size means MAC DA + MAC SA + VLAN header + Ethertype + L2 payload,
>> > > and without FCS, right?
>> > 
>> > Yes.
>> > 
>> > >
>> > > Because max_sdu 128 only counts the L2 payload, so the maximum frame
>> > > size that passes should be 142 octets, or 146 octets with VLAN.
>> > 
>> > Ok, i see. So, for 128 max-sdu we should end up with something like this
>> > in the prio config register:
>> > 
>> >  schedule->max_sdu[tc] + VLAN_ETH_HLEN - 4
>> 
>> What does 4 represent? ETH_FCS_LEN?
>> 
>> So when schedule->max_sdu[tc] is 128, you write to HR_PTPRTCCFG_MAXSDU
>> the value of 128 + 18 - 4 = 142, and this will pass packets (VLAN-tagged
>> or not) with an skb->len (on xmit) <= 142, right?
>
> Mistake, I meant skb->len <= 146 (max_sdu[tc] + VLAN_ETH_HLEN). So the
> hardware calculates the max frame len to include FCS, and skb->len is
> without FCS, hence the 4 discrepancy.

Yes, seems like it.

In case you repost this series, can you replace your patch with the one
below?

From 6488e0f979f3ea8c6130beb1b3e661cdb7796916 Mon Sep 17 00:00:00 2001
From: Kurt Kanzenbach <[email-masked]>
Date: Wed, 14 Sep 2022 19:51:40 +0200
Subject: [PATCH] net: dsa: hellcreek: Offload per-tc max SDU from tc-taprio

Add support for configuring the max SDU per priority and per port. If not
specified, keep the default.

Signed-off-by: Kurt Kanzenbach <[email-masked]>
---
 drivers/net/dsa/hirschmann/hellcreek.c | 64 +++++++++++++++++++++++---
 drivers/net/dsa/hirschmann/hellcreek.h |  7 +++
 2 files changed, 64 insertions(+), 7 deletions(-)

diff --git a/drivers/net/dsa/hirschmann/hellcreek.c b/drivers/net/dsa/hirschmann/hellcreek.c
index 5ceee71d9a25..c4b76b1e7a63 100644
--- a/drivers/net/dsa/hirschmann/hellcreek.c
+++ b/drivers/net/dsa/hirschmann/hellcreek.c
@@ -128,6 +128,16 @@ static void hellcreek_select_prio(struct hellcreek *hellcreek, int prio)
 	hellcreek_write(hellcreek, val, HR_PSEL);
 }
 
+static void hellcreek_select_port_prio(struct hellcreek *hellcreek, int port,
+				       int prio)
+{
+	u16 val = port << HR_PSEL_PTWSEL_SHIFT;
+
+	val |= prio << HR_PSEL_PRTCWSEL_SHIFT;
+
+	hellcreek_write(hellcreek, val, HR_PSEL);
+}
+
 static void hellcreek_select_counter(struct hellcreek *hellcreek, int counter)
 {
 	u16 val = counter << HR_CSEL_SHIFT;
@@ -1537,6 +1547,45 @@ hellcreek_port_prechangeupper(struct dsa_switch *ds, int port,
 	return ret;
 }
 
+static void hellcreek_setup_maxsdu(struct hellcreek *hellcreek, int port,
+				   const struct tc_taprio_qopt_offload *schedule)
+{
+	int tc;
+
+	for (tc = 0; tc < 8; ++tc) {
+		u32 max_sdu = schedule->max_sdu[tc] + VLAN_ETH_HLEN - ETH_FCS_LEN;
+		u16 val;
+
+		if (!schedule->max_sdu[tc])
+			continue;
+
+		dev_dbg(hellcreek->dev, "Configure max-sdu %u for tc %d on port %d\n",
+			max_sdu, tc, port);
+
+		hellcreek_select_port_prio(hellcreek, port, tc);
+
+		val = (max_sdu & HR_PTPRTCCFG_MAXSDU_MASK) << HR_PTPRTCCFG_MAXSDU_SHIFT;
+
+		hellcreek_write(hellcreek, val, HR_PTPRTCCFG);
+	}
+}
+
+static void hellcreek_reset_maxsdu(struct hellcreek *hellcreek, int port)
+{
+	int tc;
+
+	for (tc = 0; tc < 8; ++tc) {
+		u16 val;
+
+		hellcreek_select_port_prio(hellcreek, port, tc);
+
+		val = (HELLCREEK_DEFAULT_MAX_SDU & HR_PTPRTCCFG_MAXSDU_MASK)
+			<< HR_PTPRTCCFG_MAXSDU_SHIFT;
+
+		hellcreek_write(hellcreek, val, HR_PTPRTCCFG);
+	}
+}
+
 static void hellcreek_setup_gcl(struct hellcreek *hellcreek, int port,
 				const struct tc_taprio_qopt_offload *schedule)
 {
@@ -1720,7 +1769,10 @@ static int hellcreek_port_set_schedule(struct dsa_switch *ds, int port,
 	}
 	hellcreek_port->current_schedule = taprio_offload_get(taprio);
 
-	/* Then select port */
+	/* Configure max sdu */
+	hellcreek_setup_maxsdu(hellcreek, port, hellcreek_port->current_schedule);
+
+	/* Select tdg */
 	hellcreek_select_tgd(hellcreek, port);
 
 	/* Enable gating and keep defaults */
@@ -1772,7 +1824,10 @@ static int hellcreek_port_del_schedule(struct dsa_switch *ds, int port)
 		hellcreek_port->current_schedule = NULL;
 	}
 
-	/* Then select port */
+	/* Reset max sdu */
+	hellcreek_reset_maxsdu(hellcreek, port);
+
+	/* Select tgd */
 	hellcreek_select_tgd(hellcreek, port);
 
 	/* Disable gating and return to regular switching flow */
@@ -1814,15 +1869,10 @@ static int hellcreek_port_setup_tc(struct dsa_switch *ds, int port,
 {
 	struct tc_taprio_qopt_offload *taprio = type_data;
 	struct hellcreek *hellcreek = ds->priv;
-	int tc;
 
 	if (type != TC_SETUP_QDISC_TAPRIO)
 		return -EOPNOTSUPP;
 
-	for (tc = 0; tc < TC_MAX_QUEUE; tc++)
-		if (taprio->max_sdu[tc])
-			return -EOPNOTSUPP;
-
 	if (!hellcreek_validate_schedule(hellcreek, taprio))
 		return -EOPNOTSUPP;
 
diff --git a/drivers/net/dsa/hirschmann/hellcreek.h b/drivers/net/dsa/hirschmann/hellcreek.h
index c96b8c278904..66b989d946e4 100644
--- a/drivers/net/dsa/hirschmann/hellcreek.h
+++ b/drivers/net/dsa/hirschmann/hellcreek.h
@@ -37,6 +37,7 @@
 #define HELLCREEK_VLAN_UNTAGGED_MEMBER	0x1
 #define HELLCREEK_VLAN_TAGGED_MEMBER	0x3
 #define HELLCREEK_NUM_EGRESS_QUEUES	8
+#define HELLCREEK_DEFAULT_MAX_SDU	1536
 
 /* Register definitions */
 #define HR_MODID_C			(0 * 2)
@@ -72,6 +73,12 @@
 #define HR_PRTCCFG_PCP_TC_MAP_SHIFT	0
 #define HR_PRTCCFG_PCP_TC_MAP_MASK	GENMASK(2, 0)
 
+#define HR_PTPRTCCFG			(0xa9 * 2)
+#define HR_PTPRTCCFG_SET_QTRACK		BIT(15)
+#define HR_PTPRTCCFG_REJECT		BIT(14)
+#define HR_PTPRTCCFG_MAXSDU_SHIFT	0
+#define HR_PTPRTCCFG_MAXSDU_MASK	GENMASK(10, 0)
+
 #define HR_CSEL				(0x8d * 2)
 #define HR_CSEL_SHIFT			0
 #define HR_CSEL_MASK			GENMASK(7, 0)
-- 
2.30.2