serial: sirf: use hrtimer for data rx

when the serial works as a bluetooth sink, due to audio realtime
requirement, the driver should have something similar with ALSA:
1. one big DMA buffer to easy the schedule jitter
2. split this big DMA buffer to multiple small periods, for each
period, we get a DMA interrupt, then push the data to userspace.
the small periods will easy the audio latency.

so ALSA generally uses a cyclic chained DMA.

but for sirfsoc, the dma hardware has the limitation: we have
only two loops in the cyclic mode, so we can only support two
small periods to switch. if we make the DMA buffer too big, we
get long latency, if we make the DMA buffer too little, we get
miss in scheduling for audio realtime.

so this patch moves to use a hrtimer to simulate the cyclic
DMA, then we can have a big buffer, and also have a timely
data push to users as the hrtimer can generate in small period
then actual HW interrupts.

with this patch, we also delete a lot of complex codes to handle
loop buffers, and RX timeout interrupt since the RX work can be
completely handled from hrtimer interrupt.

tests show using this way will make our bad audio streaming be-
come smooth.
Signed-off-by: Qipan Li <Qipan.Li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sirfsoc_uart.h

@@ -7,6 +7,7 @@
  */
 #include <linux/bitops.h>
 #include <linux/log2.h>
+#include <linux/hrtimer.h>
 struct sirfsoc_uart_param {
 	const char *uart_name;
 	const char *port_name;
@@ -293,6 +294,7 @@ struct sirfsoc_uart_register sirfsoc_uart = {
 
 #define SIRFUART_IO_MODE			BIT(0)
 #define SIRFUART_DMA_MODE			0x0
+#define SIRFUART_RX_DMA_FLUSH			0x4
 
 /* Baud Rate Calculation */
 #define SIRF_USP_MIN_SAMPLE_DIV			0x1
@@ -353,8 +355,7 @@ struct sirfsoc_uart_register sirfsoc_uart = {
 				 uint_st->sirfsoc_rx_timeout)
 #define SIRFUART_CTS_INT_ST(uint_st)	(uint_st->sirfsoc_cts)
 #define SIRFUART_RX_DMA_INT_EN(uint_en, uart_type)		\
-				(uint_en->sirfsoc_rx_timeout_en |\
-				 uint_en->sirfsoc_frm_err_en |\
+				(uint_en->sirfsoc_frm_err_en |\
 				 uint_en->sirfsoc_rx_oflow_en |\
 				 uint_en->sirfsoc_rxd_brk_en |\
 				((uart_type != SIRF_REAL_UART) ? \
@@ -369,7 +370,7 @@ struct sirfsoc_uart_register sirfsoc_uart = {
 #define SIRFSOC_PORT_TYPE			0xa5
 
 /* Uart Common Use Macro*/
-#define SIRFSOC_RX_DMA_BUF_SIZE	256
+#define SIRFSOC_RX_DMA_BUF_SIZE		(1024 * 32)
 #define BYTES_TO_ALIGN(dma_addr)	((unsigned long)(dma_addr) & 0x3)
 /* Uart Fifo Level Chk */
 #define SIRFUART_TX_FIFO_SC_OFFSET	0
@@ -385,8 +386,8 @@ struct sirfsoc_uart_register sirfsoc_uart = {
 #define SIRFUART_RX_FIFO_CHK_SC SIRFUART_TX_FIFO_CHK_SC
 #define	SIRFUART_RX_FIFO_CHK_LC SIRFUART_TX_FIFO_CHK_LC
 #define SIRFUART_RX_FIFO_CHK_HC SIRFUART_TX_FIFO_CHK_HC
+#define SIRFUART_RX_FIFO_MASK 0x7f
 /* Indicate how many buffers used */
-#define SIRFSOC_RX_LOOP_BUF_CNT		2
 
 /* For Fast Baud Rate Calculation */
 struct sirfsoc_baudrate_to_regv {
@@ -400,7 +401,7 @@ enum sirfsoc_tx_state {
 	TX_DMA_PAUSE,
 };
 
-struct sirfsoc_loop_buffer {
+struct sirfsoc_rx_buffer {
 	struct circ_buf			xmit;
 	dma_cookie_t			cookie;
 	struct dma_async_tx_descriptor	*desc;
@@ -420,17 +421,16 @@ struct sirfsoc_uart_port {
 	struct dma_chan			*tx_dma_chan;
 	dma_addr_t			tx_dma_addr;
 	struct dma_async_tx_descriptor	*tx_dma_desc;
-	struct tasklet_struct		rx_dma_complete_tasklet;
-	struct tasklet_struct		rx_tmo_process_tasklet;
 	unsigned int			rx_io_count;
 	unsigned long			transfer_size;
 	enum sirfsoc_tx_state		tx_dma_state;
 	unsigned int			cts_gpio;
 	unsigned int			rts_gpio;
 
-	struct sirfsoc_loop_buffer	rx_dma_items[SIRFSOC_RX_LOOP_BUF_CNT];
-	int				rx_completed;
-	int				rx_issued;
+	struct sirfsoc_rx_buffer	rx_dma_items;
+	struct hrtimer			hrt;
+	bool				is_hrt_enabled;
+	unsigned long			rx_period_time;
 };
 
 /* Register Access Control */