greybus: gb-beagleplay: propagate hdlc_tx_frames() errors to callers

Now that hdlc_tx_frames() can drop frames when the circular buffer is
full, make the failure visible to callers:

 - Change hdlc_tx_frames() return type from void to int (-EAGAIN on
   buffer full).
 - Change gb_beagleplay_start_svc() / gb_beagleplay_stop_svc() to
   return int so probe and firmware-upload paths can detect failures.
 - gb_message_send(): propagate the error so the greybus core can
   handle the transport failure.
 - hdlc_tx_s_frame_ack(): log with dev_warn_ratelimited on failure
   (ACK loss is recoverable by HDLC retransmission).
 - Probe path: propagate start_svc failure via new free_greybus label.
 - Firmware upload paths: return FW_UPLOAD_ERR_RW_ERROR when SVC
   restart fails instead of silently continuing.
 - Remove path: best-effort stop_svc, ignore failure.

Cc: Ayush Singh <ayushdevel1325@gmail.com>
Cc: Johan Hovold <johan@kernel.org>
Cc: Alex Elder <elder@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Weigang He <geoffreyhe2@gmail.com>
Link: https://patch.msgid.link/20260330120801.981506-2-geoffreyhe2@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/greybus/gb-beagleplay.c b/drivers/greybus/gb-beagleplay.c
index 79ae3ef8698ee4d02920691f6c33096105dccf91..305066febbe7770a565a66b214c3bfaa89c922c8 100644 (file)
--- a/drivers/greybus/gb-beagleplay.c
+++ b/drivers/greybus/gb-beagleplay.c
@@ -314,6 +314,9 @@ static void hdlc_transmit(struct work_struct *work)
  * @payloads: array of payload buffers
  * @count: number of payloads
  *
+ * Every data byte may need HDLC escaping (doubling its size).
+ * Frame layout: flag(1) + address(1-2) + control(1-2) + payload + CRC(2-4) + flag(1).
+ *
  * Returns the maximum number of bytes needed in the circular buffer.
  */
 static size_t hdlc_encoded_length(const struct hdlc_payload payloads[],
@@ -348,8 +351,10 @@ static size_t hdlc_encoded_length(const struct hdlc_payload payloads[],
  * available, then verifies space under the lock and writes the entire
  * frame atomically.  Either a complete frame is enqueued or nothing is
  * written, avoiding both sleeping in atomic context and partial frames.
+ *
+ * Returns 0 on success, -EAGAIN if the buffer remains full after retries.
  */
-static void hdlc_tx_frames(struct gb_beagleplay *bg, u8 address, u8 control,
+static int hdlc_tx_frames(struct gb_beagleplay *bg, u8 address, u8 control,
                           const struct hdlc_payload payloads[], size_t count)
 {
        size_t needed = hdlc_encoded_length(payloads, count);
@@ -372,25 +377,24 @@ static void hdlc_tx_frames(struct gb_beagleplay *bg, u8 address, u8 control,
        }
 
        if (retries < 0) {
-               dev_warn_ratelimited(&bg->sd->dev,
-                                    "Tx circ buf full, dropping frame\n");
-               return;
+               dev_warn_ratelimited(&bg->sd->dev, "Tx circ buf full, dropping frame\n");
+               return -EAGAIN;
        }
 
        spin_lock(&bg->tx_producer_lock);
 
        /*
-        * Re-check under the lock.  Should not fail since
-        * tx_producer_lock serialises all producers and the
-        * consumer only frees space, but guard against it.
+        * Re-check space under the lock to close the TOCTOU window.
+        * This should be rare since tx_producer_lock serialises all
+        * producers and the consumer only frees space.  If it fires,
+        * the caller is expected to handle -EAGAIN (retry or report).
         */
        head = bg->tx_circ_buf.head;
        tail = READ_ONCE(bg->tx_circ_buf.tail);
        if (unlikely(CIRC_SPACE(head, tail, TX_CIRC_BUF_SIZE) < needed)) {
                spin_unlock(&bg->tx_producer_lock);
-               dev_warn_ratelimited(&bg->sd->dev,
-                                    "Tx circ buf space lost, dropping frame\n");
-               return;
+               dev_warn_ratelimited(&bg->sd->dev, "Tx circ buf space lost, dropping frame\n");
+               return -EAGAIN;
        }
 
        hdlc_append_tx_frame(bg);
@@ -406,11 +410,16 @@ static void hdlc_tx_frames(struct gb_beagleplay *bg, u8 address, u8 control,
        spin_unlock(&bg->tx_producer_lock);
 
        schedule_work(&bg->tx_work);
+       return 0;
 }
 
 static void hdlc_tx_s_frame_ack(struct gb_beagleplay *bg)
 {
-       hdlc_tx_frames(bg, bg->rx_buffer[0], (bg->rx_buffer[1] >> 1) & 0x7, NULL, 0);
+       int ret;
+
+       ret = hdlc_tx_frames(bg, bg->rx_buffer[0], (bg->rx_buffer[1] >> 1) & 0x7, NULL, 0);
+       if (ret)
+               dev_warn_ratelimited(&bg->sd->dev, "Failed to send HDLC ACK: %d\n", ret);
 }
 
 static void hdlc_rx_frame(struct gb_beagleplay *bg)
@@ -674,6 +683,7 @@ static int gb_message_send(struct gb_host_device *hd, u16 cport, struct gb_messa
        struct gb_beagleplay *bg = dev_get_drvdata(&hd->dev);
        struct hdlc_payload payloads[3];
        __le16 cport_id = cpu_to_le16(cport);
+       int ret;
 
        dev_dbg(&hd->dev, "Sending greybus message with Operation %u, Type: %X on Cport %u",
                msg->header->operation_id, msg->header->type, cport);
@@ -688,7 +698,10 @@ static int gb_message_send(struct gb_host_device *hd, u16 cport, struct gb_messa
        payloads[2].buf = msg->payload;
        payloads[2].len = msg->payload_size;
 
-       hdlc_tx_frames(bg, ADDRESS_GREYBUS, 0x03, payloads, 3);
+       ret = hdlc_tx_frames(bg, ADDRESS_GREYBUS, 0x03, payloads, 3);
+       if (ret)
+               return ret;
+
        greybus_message_sent(bg->gb_hd, msg, 0);
 
        return 0;
@@ -701,20 +714,20 @@ static void gb_message_cancel(struct gb_message *message)
 static struct gb_hd_driver gb_hdlc_driver = { .message_send = gb_message_send,
                                              .message_cancel = gb_message_cancel };
 
-static void gb_beagleplay_start_svc(struct gb_beagleplay *bg)
+static int gb_beagleplay_start_svc(struct gb_beagleplay *bg)
 {
        const u8 command = CONTROL_SVC_START;
        const struct hdlc_payload payload = { .len = 1, .buf = (void *)&command };
 
-       hdlc_tx_frames(bg, ADDRESS_CONTROL, 0x03, &payload, 1);
+       return hdlc_tx_frames(bg, ADDRESS_CONTROL, 0x03, &payload, 1);
 }
 
-static void gb_beagleplay_stop_svc(struct gb_beagleplay *bg)
+static int gb_beagleplay_stop_svc(struct gb_beagleplay *bg)
 {
        const u8 command = CONTROL_SVC_STOP;
        const struct hdlc_payload payload = { .len = 1, .buf = (void *)&command };
 
-       hdlc_tx_frames(bg, ADDRESS_CONTROL, 0x03, &payload, 1);
+       return hdlc_tx_frames(bg, ADDRESS_CONTROL, 0x03, &payload, 1);
 }
 
 static int cc1352_bootloader_wait_for_ack(struct gb_beagleplay *bg)
@@ -952,7 +965,9 @@ static enum fw_upload_err cc1352_prepare(struct fw_upload *fw_upload,
        gb_greybus_deinit(bg);
        msleep(5 * MSEC_PER_SEC);
 
-       gb_beagleplay_stop_svc(bg);
+       /* Best effort — device is entering bootloader mode regardless. */
+       if (gb_beagleplay_stop_svc(bg))
+               dev_warn(&bg->sd->dev, "Failed to send SVC stop before flashing\n");
        msleep(200);
        flush_work(&bg->tx_work);
 
@@ -994,7 +1009,9 @@ static enum fw_upload_err cc1352_prepare(struct fw_upload *fw_upload,
                if (gb_greybus_init(bg) < 0)
                        return dev_err_probe(&bg->sd->dev, FW_UPLOAD_ERR_RW_ERROR,
                                             "Failed to initialize greybus");
-               gb_beagleplay_start_svc(bg);
+               if (gb_beagleplay_start_svc(bg))
+                       return dev_err_probe(&bg->sd->dev, FW_UPLOAD_ERR_RW_ERROR,
+                                            "Failed to restart SVC after skip");
                return FW_UPLOAD_ERR_FW_INVALID;
        }
 
@@ -1075,7 +1092,9 @@ static enum fw_upload_err cc1352_poll_complete(struct fw_upload *fw_upload)
                return dev_err_probe(&bg->sd->dev, FW_UPLOAD_ERR_RW_ERROR,
                                     "Failed to initialize greybus");
 
-       gb_beagleplay_start_svc(bg);
+       if (gb_beagleplay_start_svc(bg) < 0)
+               return dev_err_probe(&bg->sd->dev, FW_UPLOAD_ERR_RW_ERROR,
+                                    "Failed to start SVC");
 
        return FW_UPLOAD_ERR_NONE;
 }
@@ -1186,10 +1205,14 @@ static int gb_beagleplay_probe(struct serdev_device *serdev)
        if (ret)
                goto free_fw;
 
-       gb_beagleplay_start_svc(bg);
+       ret = gb_beagleplay_start_svc(bg);
+       if (ret)
+               goto free_greybus;
 
        return 0;
 
+free_greybus:
+       gb_greybus_deinit(bg);
 free_fw:
        gb_fw_deinit(bg);
 free_hdlc:
@@ -1205,6 +1228,7 @@ static void gb_beagleplay_remove(struct serdev_device *serdev)
 
        gb_fw_deinit(bg);
        gb_greybus_deinit(bg);
+       /* Best effort — device is being removed. */
        gb_beagleplay_stop_svc(bg);
        hdlc_deinit(bg);
        gb_serdev_deinit(bg);