From fc7295eb74016b51c61272ef2b990734c6453382 Mon Sep 17 00:00:00 2001
From: Jeff Epler <jepler@gmail.com>
Date: Mon, 17 Mar 2025 09:03:44 -0500
Subject: [PATCH 1/2] Actually report errors in pio_sm_xfer_data

---
 src/include/piomatter/piomatter.h | 20 +++++++++++++++++---
 src/pymain.cpp                    |  9 ++++++++-
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/include/piomatter/piomatter.h b/src/include/piomatter/piomatter.h
index c43f7ec..1143a18 100644
--- a/src/include/piomatter/piomatter.h
+++ b/src/include/piomatter/piomatter.h
@@ -26,7 +26,7 @@ struct piomatter_base {
     piomatter_base &operator=(const piomatter_base &) = delete;
 
     virtual ~piomatter_base() {}
-    virtual void show() = 0;
+    virtual int show() = 0;
 
     double fps;
 };
@@ -48,7 +48,11 @@ struct piomatter : piomatter_base {
         show();
     }
 
-    void show() override {
+    int show() override {
+        int err = pending_error_errno.exchange(0); // we're handling this error
+        if (err != 0) {
+            return err;
+        }
         int buffer_idx = manager.get_free_buffer();
         auto &bufseq = buffers[buffer_idx];
         bufseq.resize(geometry.schedules.size());
@@ -61,6 +65,7 @@ struct piomatter : piomatter_base {
             old_active_time = geometry.schedules[i].back().active_time;
         }
         manager.put_filled_buffer(buffer_idx);
+        return 0;
     }
 
     ~piomatter() {
@@ -174,7 +179,15 @@ struct piomatter : piomatter_base {
                 const auto &data = cur_buf[seq_idx];
                 auto datasize = sizeof(uint32_t) * data.size();
                 auto dataptr = const_cast<uint32_t *>(&data[0]);
-                pio_sm_xfer_data(pio, sm, PIO_DIR_TO_SM, datasize, dataptr);
+                // returns err = rp1_ioctl.... which seems to be a negative
+                // errno value
+                int r =
+                    pio_sm_xfer_data(pio, sm, PIO_DIR_TO_SM, datasize, dataptr);
+                if (r != 0) {
+                    pending_error_errno.store(-r);
+                    printf("xfer_data() returned error %d (%s)\n", r,
+                           strerror(-r));
+                }
                 t1 = monotonicns64();
                 if (t0 != t1) {
                     fps = 1e9 / (t1 - t0);
@@ -194,6 +207,7 @@ struct piomatter : piomatter_base {
     matrix_geometry geometry;
     colorspace converter;
     std::thread blitter_thread;
+    std::atomic<int> pending_error_errno;
 };
 
 } // namespace piomatter
diff --git a/src/pymain.cpp b/src/pymain.cpp
index 483b2dc..053aded 100644
--- a/src/pymain.cpp
+++ b/src/pymain.cpp
@@ -18,7 +18,14 @@ struct PyPiomatter {
     py::buffer buffer;
     std::unique_ptr<piomatter::piomatter_base> matter;
 
-    void show() { matter->show(); }
+    void show() {
+        int err = matter->show();
+        if (err != 0) {
+            errno = err;
+            PyErr_SetFromErrno(PyExc_OSError);
+            throw py::error_already_set();
+        }
+    }
     double fps() const { return matter->fps; }
 };
 

From 89dd515ae5489a9cbde3b2c1e4c9b7c62d7e2756 Mon Sep 17 00:00:00 2001
From: Jeff Epler <jepler@gmail.com>
Date: Mon, 17 Mar 2025 10:29:45 -0500
Subject: [PATCH 2/2] restore large xfer workaround

sadly, it's not possible to gracefully switch from large to blocked
xfers, further xfer ioctls fail after the first large xfer fails.
---
 src/include/piomatter/piomatter.h | 46 +++++++++++++++++++++++++++----
 1 file changed, 41 insertions(+), 5 deletions(-)

diff --git a/src/include/piomatter/piomatter.h b/src/include/piomatter/piomatter.h
index 1143a18..4ead468 100644
--- a/src/include/piomatter/piomatter.h
+++ b/src/include/piomatter/piomatter.h
@@ -12,6 +12,42 @@
 
 namespace piomatter {
 
+static int pio_sm_xfer_data_large(PIO pio, int sm, int direction, size_t size,
+                                  uint32_t *databuf) {
+#if 0
+    // it would be NICE to gracefully fall back to blocked transfer, but sadly
+    // once the large xfer ioctl fails, future small xfers fail too.
+    static enum { UNKNOWN, OK, BAD } large_xfer_status = UNKNOWN;
+    printf("large_xfer_status=%d\n", large_xfer_status);
+    if (large_xfer_status != BAD) {
+        int r = pio_sm_xfer_data(pio, sm, direction, size, databuf);
+        if (large_xfer_status == UNKNOWN && r != 0) {
+            large_xfer_status = BAD;
+            fprintf(stderr,
+                    "Transmission limit workaround engaged. May reduce quality of "
+                    "output.\nSee https://github.com/raspberrypi/utils/issues/123 "
+                    "for details.\n");
+        } else {
+            if (large_xfer_status == UNKNOWN && r == 0) {
+                large_xfer_status = OK;
+            }
+            return r;
+        }
+    }
+#endif
+    constexpr size_t MAX_XFER = 65532;
+    while (size) {
+        size_t xfersize = std::min(size_t{MAX_XFER}, size);
+        int r = pio_sm_xfer_data(pio, sm, direction, xfersize, databuf);
+        if (r != 0) {
+            return r;
+        }
+        size -= xfersize;
+        databuf += xfersize / sizeof(*databuf);
+    }
+    return 0;
+}
+
 static uint64_t monotonicns64() {
     struct timespec tp;
     clock_gettime(CLOCK_MONOTONIC, &tp);
@@ -181,12 +217,12 @@ struct piomatter : piomatter_base {
                 auto dataptr = const_cast<uint32_t *>(&data[0]);
                 // returns err = rp1_ioctl.... which seems to be a negative
                 // errno value
-                int r =
-                    pio_sm_xfer_data(pio, sm, PIO_DIR_TO_SM, datasize, dataptr);
+                int r = pio_sm_xfer_data_large(pio, sm, PIO_DIR_TO_SM, datasize,
+                                               dataptr);
                 if (r != 0) {
-                    pending_error_errno.store(-r);
-                    printf("xfer_data() returned error %d (%s)\n", r,
-                           strerror(-r));
+                    pending_error_errno.store(errno);
+                    printf("xfer_data() returned error %d (errno=%s)\n", r,
+                           strerror(errno));
                 }
                 t1 = monotonicns64();
                 if (t0 != t1) {