rohan.g.thomas@intel.com writes:

From: Rohan G Thomas <redacted>

On Fri, 26 Jan 2024 09:35:01 +0100, Esben Haabendal wrote:

quoted

quoted

+	/* If TBS feature is supported(i.e. tbssel is true), then at least 1 Tx
+	 * DMA channel supports TBS. So if tbs_ch_num is 0 and tbssel is true,
+	 * assume all Tx DMA channels support TBS. TBS_CH field, which gives
+	 * number of Tx DMA channels with TBS support is only available only

for

quoted

+	 * DW xGMAC IP. For other DWMAC IPs all Tx DMA channels can

support TBS.

The Ethernet QOS controllers found in various i.MX socs does not support TBS
on TX queue 0. I believe this patch would break the dwmac driver for these
platforms.

AFAIU from Synopsys DWMAC5 Databook, all queues support TBS. But TBS
cannot coexist with TSO. So all glue drivers enabling TBS feature are
avoiding queue 0 to support TSO. Also packets requesting TSO are
always directed to queue 0 by stmmac driver.

After re-reading the i.MX8MP documentation, and making a few
experiments, I have to agree with you. Enabling TBS (enhanced
descriptors) for Q0 should be ok on i.MX.

quoted

quoted

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3773,12 +3773,18 @@ stmmac_setup_dma_desc(struct stmmac_priv

*priv, unsigned int mtu)

quoted

 		dma_conf->dma_rx_size = DMA_DEFAULT_RX_SIZE;

 	/* Earlier check for TBS */
-	for (chan = 0; chan < priv->plat->tx_queues_to_use; chan++) {
-		struct stmmac_tx_queue *tx_q = &dma_conf-
tx_queue[chan];
-		int tbs_en = priv->plat->tx_queues_cfg[chan].tbs_en;
+	if (priv->dma_cap.tbssel) {
+		/* TBS is available only for tbs_ch_num of Tx DMA channels,
+		 * starting from the highest Tx DMA channel.
+		 */
+		chan = priv->dma_cap.number_tx_channel - priv-
dma_cap.tbs_ch_num;

For IPs which don't have tbs_ch_num, this loop goes from 0 to
number_tx_channel to check if tbs_enable is set by glue driver.
Existing logic is also the same. Unless you set tbs_en flag of
queue 0 from the glue driver or dts configuration this patch doesn't
set tbs flag for queue 0. This is a sanity check to avoid wrong
configuration for IPs which support tbs only in a few number of
queues.

Sounds good.

quoted

quoted

+		for (; chan < priv->plat->tx_queues_to_use; chan++) {
+			struct stmmac_tx_queue *tx_q = &dma_conf-
tx_queue[chan];
+			int tbs_en = priv->plat->tx_queues_cfg[chan].tbs_en;

-		/* Setup per-TXQ tbs flag before TX descriptor alloc */
-		tx_q->tbs |= tbs_en ? STMMAC_TBS_AVAIL : 0;
+			/* Setup per-TXQ tbs flag before TX descriptor alloc

*/

quoted

+			tx_q->tbs |= tbs_en ? STMMAC_TBS_AVAIL : 0;
+		}
 	}

Please correct me if I've misstated anything.

No corrections for now :)

/Esben