rohan.g.thomas@xxxxxxxxx writes: > From: Rohan G Thomas <rohan.g.thomas@xxxxxxxxx> > > On Fri, 26 Jan 2024 09:35:01 +0100, Esben Haabendal wrote: > >> > + /* 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 >> > + * 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. >> > --- 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) >> > 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. >> > + 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 >> */ >> > + tx_q->tbs |= tbs_en ? STMMAC_TBS_AVAIL : 0; >> > + } >> > } > > Please correct me if I've misstated anything. No corrections for now :) /Esben