From a3e69e715daa4693c105764519fa06771237bc40 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Mon, 18 Feb 2019 10:21:28 +1100
Subject: [PATCH] HAL_ChibiOS: avoid doing one-way SPI transfers

these transfers use dummy bytes in the hal driver, which may not be in
DMA safe memory, so best to avoid them
---
 libraries/AP_HAL_ChibiOS/Device.cpp                  |  4 ++--
 libraries/AP_HAL_ChibiOS/SPIDevice.cpp               |  8 +-------
 libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c | 12 +++++++++---
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/libraries/AP_HAL_ChibiOS/Device.cpp b/libraries/AP_HAL_ChibiOS/Device.cpp
index bf9e56f465..1281d2512a 100644
--- a/libraries/AP_HAL_ChibiOS/Device.cpp
+++ b/libraries/AP_HAL_ChibiOS/Device.cpp
@@ -161,10 +161,10 @@ bool DeviceBus::adjust_timer(AP_HAL::Device::PeriodicHandle h, uint32_t period_u
 void DeviceBus::bouncebuffer_setup(const uint8_t *&buf_tx, uint16_t tx_len,
                                    uint8_t *&buf_rx, uint16_t rx_len)
 {
-    if (buf_rx) {
+    if (rx_len != 0) {
         bouncebuffer_setup_read(bounce_buffer_rx, &buf_rx, rx_len);
     }
-    if (buf_tx) {
+    if (tx_len != 0) {
         bouncebuffer_setup_write(bounce_buffer_tx, &buf_tx, tx_len);
     }
 }
diff --git a/libraries/AP_HAL_ChibiOS/SPIDevice.cpp b/libraries/AP_HAL_ChibiOS/SPIDevice.cpp
index 328cb8e383..89bb46eea1 100644
--- a/libraries/AP_HAL_ChibiOS/SPIDevice.cpp
+++ b/libraries/AP_HAL_ChibiOS/SPIDevice.cpp
@@ -176,13 +176,7 @@ void SPIDevice::do_transfer(const uint8_t *send, uint8_t *recv, uint32_t len)
 
     bus.bouncebuffer_setup(send, len, recv, len);
 
-    if (send == nullptr) {
-        spiReceive(spi_devices[device_desc.bus].driver, len, recv);
-    } else if (recv == nullptr) {
-        spiSend(spi_devices[device_desc.bus].driver, len, send);
-    } else {
-        spiExchange(spi_devices[device_desc.bus].driver, len, send, recv);
-    }
+    spiExchange(spi_devices[device_desc.bus].driver, len, send, recv);
 
     bus.bouncebuffer_finish(send, recv, len);
 
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c b/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c
index 9b5204a549..7ae9d79c2c 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c
@@ -48,6 +48,8 @@ void bouncebuffer_init(struct bouncebuffer_t **bouncebuffer, uint32_t prealloc_b
 
 /*
   setup for reading from a device into memory, allocating a bouncebuffer if needed
+  Note that *buf can be NULL, in which case we allocate DMA capable memory, but don't
+  copy to it in bouncebuffer_finish_read(). This avoids DMA failures in dummyrx in the SPI LLD
  */
 void bouncebuffer_setup_read(struct bouncebuffer_t *bouncebuffer, uint8_t **buf, uint32_t size)
 {
@@ -79,8 +81,10 @@ void bouncebuffer_setup_read(struct bouncebuffer_t *bouncebuffer, uint8_t **buf,
 void bouncebuffer_finish_read(struct bouncebuffer_t *bouncebuffer, const uint8_t *buf, uint32_t size)
 {
     if (bouncebuffer && buf == bouncebuffer->dma_buf) {
-        osalDbgAssert((bouncebuffer->busy == true), "bouncebuffer finish_read");        
-        memcpy(bouncebuffer->orig_buf, buf, size);
+        osalDbgAssert((bouncebuffer->busy == true), "bouncebuffer finish_read");
+        if (bouncebuffer->orig_buf) {
+            memcpy(bouncebuffer->orig_buf, buf, size);
+        }
         bouncebuffer->busy = false;
     }
 }
@@ -104,7 +108,9 @@ void bouncebuffer_setup_write(struct bouncebuffer_t *bouncebuffer, const uint8_t
         osalDbgAssert((bouncebuffer->dma_buf != NULL), "bouncebuffer write allocate");
         bouncebuffer->size = size;
     }
-    memcpy(bouncebuffer->dma_buf, *buf, size);
+    if (*buf) {
+        memcpy(bouncebuffer->dma_buf, *buf, size);
+    }
     *buf = bouncebuffer->dma_buf;
 #if defined(STM32H7)
     osalDbgAssert((((uint32_t)*buf)&31) == 0, "bouncebuffer write align");