brcmfmac: reserve 2 credits for host tx control path

It is observed that sometimes when sdiod is low in tx credits in low
rssi scenarios, the data path consumes all sdiod rx all credits and
there is no sdiod rx credit available for control path causing host
and card to go out of sync resulting in link loss between host and
card. So in order to prevent it some credits are reserved for control
path.

Note that TXCTL_CREDITS can't be larger than the firmware default
credit update threshold 2; otherwise there will be a deadlock for both
side waiting for each other.
Signed-off-by: Amar Shankar <amsr@cypress.com>
Signed-off-by: Jia-Shyr Chuang <joseph.chuang@cypress.com>
Signed-off-by: Chi-Hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200610152106.175257-4-chi-hsien.lin@cypress.com

drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c

@@ -648,6 +648,8 @@ static const struct brcmf_firmware_mapping brcmf_sdio_fwnames[] = {
 	BRCMF_FW_ENTRY(CY_CC_43012_CHIP_ID, 0xFFFFFFFF, 43012)
 };
 
+#define TXCTL_CREDITS	2
+
 static void pkt_align(struct sk_buff *p, int len, int align)
 {
 	uint datalign;
@@ -661,8 +663,16 @@ static void pkt_align(struct sk_buff *p, int len, int align)
 /* To check if there's window offered */
 static bool data_ok(struct brcmf_sdio *bus)
 {
-	return (u8)(bus->tx_max - bus->tx_seq) != 0 &&
-	       ((u8)(bus->tx_max - bus->tx_seq) & 0x80) == 0;
+	/* Reserve TXCTL_CREDITS credits for txctl */
+	return (bus->tx_max - bus->tx_seq) > TXCTL_CREDITS &&
+	       ((bus->tx_max - bus->tx_seq) & 0x80) == 0;
+}
+
+/* To check if there's window offered */
+static bool txctl_ok(struct brcmf_sdio *bus)
+{
+	return (bus->tx_max - bus->tx_seq) != 0 &&
+	       ((bus->tx_max - bus->tx_seq) & 0x80) == 0;
 }
 
 static int
@@ -2668,7 +2678,7 @@ static void brcmf_sdio_dpc(struct brcmf_sdio *bus)
 	brcmf_sdio_clrintr(bus);
 
 	if (bus->ctrl_frame_stat && (bus->clkstate == CLK_AVAIL) &&
-	    data_ok(bus)) {
+	    txctl_ok(bus)) {
 		sdio_claim_host(bus->sdiodev->func1);
 		if (bus->ctrl_frame_stat) {
 			err = brcmf_sdio_tx_ctrlframe(bus,  bus->ctrl_frame_buf,
@@ -2676,6 +2686,9 @@ static void brcmf_sdio_dpc(struct brcmf_sdio *bus)
 			bus->ctrl_frame_err = err;
 			wmb();
 			bus->ctrl_frame_stat = false;
+			if (err)
+				brcmf_err("sdio ctrlframe tx failed err=%d\n",
+					  err);
 		}
 		sdio_release_host(bus->sdiodev->func1);
 		brcmf_sdio_wait_event_wakeup(bus);