hw/dma/xlnx_csu_dma: Support starting a read transfer through a class…

… method

An option on real hardware when embedding a DMA engine into a peripheral
is to make the peripheral control the engine through a custom DMA control
(hardware) interface between the two. Software drivers in this scenario
configure and trigger DMA operations through the controlling peripheral's
register API (for example, writing a specific bit in a register could
propagate down to a transfer start signal on the DMA control interface).
At the same time the status, results and interrupts for the transfer might
still be intended to be read and caught through the DMA engine's register
API (and signals).

This patch adds a class 'read' method for allowing to start read transfers
from peripherals embedding and controlling the Xilinx CSU DMA engine as in
above scenario.

Signed-off-by: Francisco Iglesias <francisco.iglesias@xilinx.com>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Message-id: 20220121161141.14389-6-francisco.iglesias@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/dma/xlnx_csu_dma.c

@@ -472,6 +472,20 @@ static uint64_t addr_msb_pre_write(RegisterInfo *reg, uint64_t val)
     return val & R_ADDR_MSB_ADDR_MSB_MASK;
 }
 
+static MemTxResult xlnx_csu_dma_class_read(XlnxCSUDMA *s, hwaddr addr,
+                                           uint32_t len)
+{
+    RegisterInfo *reg = &s->regs_info[R_SIZE];
+    uint64_t we = MAKE_64BIT_MASK(0, 4 * 8);
+
+    s->regs[R_ADDR] = addr;
+    s->regs[R_ADDR_MSB] = (uint64_t)addr >> 32;
+
+    register_write(reg, len, we, object_get_typename(OBJECT(s)), false);
+
+    return (s->regs[R_SIZE] == 0) ? MEMTX_OK : MEMTX_ERROR;
+}
+
 static const RegisterAccessInfo *xlnx_csu_dma_regs_info[] = {
 #define DMACH_REGINFO(NAME, snd)                                              \
     (const RegisterAccessInfo []) {                                           \
@@ -696,6 +710,7 @@ static void xlnx_csu_dma_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     StreamSinkClass *ssc = STREAM_SINK_CLASS(klass);
+    XlnxCSUDMAClass *xcdc = XLNX_CSU_DMA_CLASS(klass);
 
     dc->reset = xlnx_csu_dma_reset;
     dc->realize = xlnx_csu_dma_realize;
@@ -704,6 +719,8 @@ static void xlnx_csu_dma_class_init(ObjectClass *klass, void *data)
 
     ssc->push = xlnx_csu_dma_stream_push;
     ssc->can_push = xlnx_csu_dma_stream_can_push;
+
+    xcdc->read = xlnx_csu_dma_class_read;
 }
 
 static void xlnx_csu_dma_init(Object *obj)

include/hw/dma/xlnx_csu_dma.h

@@ -51,7 +51,22 @@ typedef struct XlnxCSUDMA {
     RegisterInfo regs_info[XLNX_CSU_DMA_R_MAX];
 } XlnxCSUDMA;
 
-#define XLNX_CSU_DMA(obj) \
-    OBJECT_CHECK(XlnxCSUDMA, (obj), TYPE_XLNX_CSU_DMA)
+OBJECT_DECLARE_TYPE(XlnxCSUDMA, XlnxCSUDMAClass, XLNX_CSU_DMA)
+
+struct XlnxCSUDMAClass {
+    SysBusDeviceClass parent_class;
+
+    /*
+     * read: Start a read transfer on a Xilinx CSU DMA engine
+     *
+     * @s: the Xilinx CSU DMA engine to start the transfer on
+     * @addr: the address to read
+     * @len: the number of bytes to read at 'addr'
+     *
+     * @return a MemTxResult indicating whether the operation succeeded ('len'
+     * bytes were read) or failed.
+     */
+    MemTxResult (*read)(XlnxCSUDMA *s, hwaddr addr, uint32_t len);
+};
 
 #endif