tty: serial: tegra: Optimize DMA buffer synchronization

Synchronize only the dirty part of DMA buffer in order to avoid
unnecessary overhead of syncing of the clean part, which is the case
of every serial DMA transfer in practice.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20200112180919.5194-3-digetx@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
index 3b495e7c9534572947cbbc9a9f6b0e7de076a2f7..33034b852a51fa52238d7d86c0ea7329170e967f 100644 (file)
--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -534,11 +534,12 @@ static int tegra_uart_start_tx_dma(struct tegra_uart_port *tup,
        struct circ_buf *xmit = &tup->uport.state->xmit;
        dma_addr_t tx_phys_addr;
 
-       dma_sync_single_for_device(tup->uport.dev, tup->tx_dma_buf_phys,
-                               UART_XMIT_SIZE, DMA_TO_DEVICE);
-
        tup->tx_bytes = count & ~(0xF);
        tx_phys_addr = tup->tx_dma_buf_phys + xmit->tail;
+
+       dma_sync_single_for_device(tup->uport.dev, tx_phys_addr,
+                                  tup->tx_bytes, DMA_TO_DEVICE);
+
        tup->tx_dma_desc = dmaengine_prep_slave_single(tup->tx_dma_chan,
                                tx_phys_addr, tup->tx_bytes, DMA_MEM_TO_DEV,
                                DMA_PREP_INTERRUPT);
@@ -680,7 +681,7 @@ static void tegra_uart_copy_rx_to_tty(struct tegra_uart_port *tup,
                return;
 
        dma_sync_single_for_cpu(tup->uport.dev, tup->rx_dma_buf_phys,
-                               TEGRA_UART_RX_DMA_BUFFER_SIZE, DMA_FROM_DEVICE);
+                               count, DMA_FROM_DEVICE);
        copied = tty_insert_flip_string(tty,
                        ((unsigned char *)(tup->rx_dma_buf_virt)), count);
        if (copied != count) {
@@ -688,7 +689,7 @@ static void tegra_uart_copy_rx_to_tty(struct tegra_uart_port *tup,
                dev_err(tup->uport.dev, "RxData copy to tty layer failed\n");
        }
        dma_sync_single_for_device(tup->uport.dev, tup->rx_dma_buf_phys,
-                               TEGRA_UART_RX_DMA_BUFFER_SIZE, DMA_TO_DEVICE);
+                                  count, DMA_TO_DEVICE);
 }
 
 static void tegra_uart_rx_buffer_push(struct tegra_uart_port *tup,
@@ -788,8 +789,6 @@ static int tegra_uart_start_rx_dma(struct tegra_uart_port *tup)
        tup->rx_dma_active = true;
        tup->rx_dma_desc->callback = tegra_uart_rx_dma_complete;
        tup->rx_dma_desc->callback_param = tup;
-       dma_sync_single_for_device(tup->uport.dev, tup->rx_dma_buf_phys,
-                               count, DMA_TO_DEVICE);
        tup->rx_bytes_requested = count;
        tup->rx_cookie = dmaengine_submit(tup->rx_dma_desc);
        dma_async_issue_pending(tup->rx_dma_chan);
@@ -1154,6 +1153,9 @@ static int tegra_uart_dma_channel_allocate(struct tegra_uart_port *tup,
                        dma_release_channel(dma_chan);
                        return -ENOMEM;
                }
+               dma_sync_single_for_device(tup->uport.dev, dma_phys,
+                                          TEGRA_UART_RX_DMA_BUFFER_SIZE,
+                                          DMA_TO_DEVICE);
                dma_sconfig.src_addr = tup->uport.mapbase;
                dma_sconfig.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
                dma_sconfig.src_maxburst = tup->cdata->max_dma_burst_bytes;