rtl8180: disable buggy rate fallback mechanism
Currently the driver configures mac80211 to provide two rates for each TX frame: One initial rate and one alternate fallback rate, each one with its retry count. HW does not support fully this: rtl8180 doesn't have support for rate scaling at all, and rtl8185/rtl8187SE supports it in a way that does not fit with mac80211: The HW does automatically fall back to the next lower rate, and only a lower limit can be specified, so the HW may TX also on rates in between the two rates specified by mac80211. Furthermore only the total TX retry count can be specified for each packet, while the number of TX attempts before scaling rate can be configured only globally (not per each packet). Currently the driver sets the HW auto rate fallback mechanism to quickly scale rate after a couple of retries, and it uses the alternate rate requested by mac80211 as fallback limit rate (and it does this even wrongly). The HW indeed will behave differently than what mac80211 mandates, that is probably undesirable, and the reported TX retry count may not refer to what mac80211 thinks, and this could fool mac80211. This patch makes the driver to declare to mac80211 to support only one rate configuration for each packet, and it does disable the HW auto rate fallback mechanism, relying only on SW and letting mac80211 to do all by itself. This should ensure correct operation and fairness respect to mac80211. Indeed here tests with iperf do not show significant performance differences. Signed-off-by: Andrea Merello <andrea.merello@gmail.com> Signed-off-by: John W. Linville <linville@tuxdriver.com>
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@ -348,7 +348,6 @@ static void rtl8180_handle_tx(struct ieee80211_hw *dev, unsigned int prio)
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info->flags |= IEEE80211_TX_STAT_ACK;
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info->status.rates[0].count = (flags & 0xFF) + 1;
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info->status.rates[1].idx = -1;
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ieee80211_tx_status_irqsafe(dev, skb);
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if (ring->entries - skb_queue_len(&ring->queue) == 2)
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@ -540,8 +539,6 @@ static void rtl8180_tx(struct ieee80211_hw *dev,
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entry->plcp_len = cpu_to_le16(plcp_len);
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entry->tx_buf = cpu_to_le32(mapping);
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entry->flags2 = info->control.rates[1].idx >= 0 ?
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ieee80211_get_alt_retry_rate(dev, info, 0)->bitrate << 4 : 0;
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entry->retry_limit = info->control.rates[0].count - 1;
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/* We must be sure that tx_flags is written last because the HW
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@ -864,7 +861,7 @@ static int rtl8180_init_hw(struct ieee80211_hw *dev)
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if (priv->chip_family != RTL818X_CHIP_FAMILY_RTL8180) {
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rtl818x_iowrite8(priv, &priv->map->WPA_CONF, 0);
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rtl818x_iowrite8(priv, &priv->map->RATE_FALLBACK, 0x81);
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rtl818x_iowrite8(priv, &priv->map->RATE_FALLBACK, 0);
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} else {
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rtl818x_iowrite8(priv, &priv->map->SECURITY, 0);
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@ -1738,7 +1735,7 @@ static int rtl8180_probe(struct pci_dev *pdev,
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priv = dev->priv;
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priv->pdev = pdev;
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dev->max_rates = 2;
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dev->max_rates = 1;
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SET_IEEE80211_DEV(dev, &pdev->dev);
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pci_set_drvdata(pdev, dev);
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