From 824f4b7b89b11559e8eb0f1f766adafd426a6ed5 Mon Sep 17 00:00:00 2001
From: Eero Nurkkala <eero.nurkkala@offcode.fi>
Date: Tue, 28 Nov 2023 13:18:32 +0200
Subject: [PATCH] risc-v/mpfs: usb: fix fierce cpu polling if remote closes

If the remote end just closes an endpoint and no longer handles it,
the system is prone to intensive cpu polling via mpfs_write_tx_fifo()
especially if the device side doesn't know a thing about what the
remote did.

Fix this by marking the EP as dead, which will skip all writes causing
unnecessary polling. The EP is back in business if the remote end
sends some data (rx) or the connection is re-established.

Signed-off-by: Eero Nurkkala <eero.nurkkala@offcode.fi>
---
 arch/risc-v/src/mpfs/hardware/mpfs_usb.h |  1 +
 arch/risc-v/src/mpfs/mpfs_usb.c          | 68 +++++++++++++++++++++---
 2 files changed, 61 insertions(+), 8 deletions(-)

diff --git a/arch/risc-v/src/mpfs/hardware/mpfs_usb.h b/arch/risc-v/src/mpfs/hardware/mpfs_usb.h
index 863044d8ddd9a..25264faf0e869 100644
--- a/arch/risc-v/src/mpfs/hardware/mpfs_usb.h
+++ b/arch/risc-v/src/mpfs/hardware/mpfs_usb.h
@@ -419,6 +419,7 @@ struct mpfs_ep_s
   struct mpfs_rqhead_s  reqq;         /* Read/write request queue */
   struct mpfs_rqhead_s  pendq;        /* Write requests pending stall sent */
   struct usbdev_epdesc_s *descb[2];   /* Pointers to this endpoint descriptors */
+  uint32_t              linkdead;     /* Remote end has closed the connection */
   volatile uint8_t      epstate;      /* State of the endpoint (see enum mpfs_epstate_e) */
   uint8_t               stalled:1;    /* true: Endpoint is stalled */
   uint8_t               pending:1;    /* true: IN Endpoint stall is pending */
diff --git a/arch/risc-v/src/mpfs/mpfs_usb.c b/arch/risc-v/src/mpfs/mpfs_usb.c
index 8f0e11bc20e1c..cfb8d6264951d 100644
--- a/arch/risc-v/src/mpfs/mpfs_usb.c
+++ b/arch/risc-v/src/mpfs/mpfs_usb.c
@@ -133,6 +133,8 @@
 #define MPFS_MIN_EP_FIFO_SIZE 8
 #define MPFS_USB_REG_MAX      0x2000
 
+#define LINKDEAD_THRESHOLD    20
+
 /* Request queue operations *************************************************/
 
 #define mpfs_rqempty(q)      ((q)->head == NULL)
@@ -229,6 +231,7 @@ static void   mpfs_epset_reset(struct mpfs_usbdev_s *priv, uint16_t epset);
 
 static struct mpfs_usbdev_s g_usbd;
 static uint8_t g_clkrefs;
+static bool    g_linkdead;
 
 static const struct usbdev_epops_s g_epops =
 {
@@ -772,11 +775,26 @@ static int mpfs_req_wrsetup(struct mpfs_usbdev_s *priv,
 
   if (nbytes > packetsize)
     {
-      ret = mpfs_write_tx_fifo(buf, packetsize, epno);
-      if (ret != OK)
+      if (privep->linkdead < LINKDEAD_THRESHOLD)
         {
-          privep->epstate = USB_EPSTATE_IDLE;
-          return ret;
+          ret = mpfs_write_tx_fifo(buf, packetsize, epno);
+          if (ret != OK)
+            {
+              privep->linkdead++;
+              privep->epstate = USB_EPSTATE_IDLE;
+              return ret;
+            }
+          else
+            {
+              privep->linkdead = 0;
+            }
+        }
+      else
+        {
+          /* We're in trouble, remote has likely closed */
+
+          g_linkdead = true;
+          return -EIO;
         }
 
       if (epno == EP0)
@@ -797,11 +815,26 @@ static int mpfs_req_wrsetup(struct mpfs_usbdev_s *priv,
     }
   else
     {
-      ret = mpfs_write_tx_fifo(buf, nbytes, epno);
-      if (ret != OK)
+      if (privep->linkdead < LINKDEAD_THRESHOLD)
         {
-          privep->epstate = USB_EPSTATE_IDLE;
-          return ret;
+          ret = mpfs_write_tx_fifo(buf, nbytes, epno);
+          if (ret != OK)
+            {
+              privep->linkdead++;
+              privep->epstate = USB_EPSTATE_IDLE;
+              return ret;
+            }
+          else
+            {
+              privep->linkdead = 0;
+            }
+        }
+      else
+        {
+          /* We're in trouble, remote has likely closed */
+
+          g_linkdead = true;
+          return -EIO;
         }
     }
 
@@ -2444,6 +2477,8 @@ static void mpfs_reset(struct mpfs_usbdev_s *priv)
 
       mpfs_req_cancel(privep, -ESHUTDOWN);
 
+      privep->linkdead  = 0;
+
       /* Reset endpoint status */
 
       privep->stalled   = false;
@@ -3456,11 +3491,28 @@ static int mpfs_usb_interrupt(int irq, void *context, void *arg)
     {
       for (i = 0; i < MPFS_USB_NENDPOINTS; i++)
         {
+          /* Check if dead connections are back in business */
+
+          if (g_linkdead)
+            {
+              /* This releases all, which is a problem if only some
+               * endpoints are closed on the remote; whereas some
+               * are functioning; for example ACM and mass storage;
+               * now the functioning one likely marks the closed ones
+               * as no longer dead.
+               */
+
+              struct mpfs_ep_s *privep = &priv->eplist[i];
+              privep->linkdead = 0;
+            }
+
           if ((pending_rx_ep & (1 << i)) != 0)
             {
               mpfs_ep_rx_interrupt(priv, i);
             }
         }
+
+      g_linkdead = false;
     }
 
   if ((isr & SUSPEND_IRQ_MASK) != 0)