From 736cd79f483fd7a1e0b71e6eaddf01d8d87fbbbb Mon Sep 17 00:00:00 2001 From: Robert Baldyga Date: Fri, 31 Jul 2015 10:58:28 +0200 Subject: [PATCH] serial: samsung: fix DMA for FIFO smaller than cache line size So far DMA mode were activated when only number of bytes to send was equal or greater than min_dma_size. Due to requirement that DMA transaction buffer should be aligned to cache line size, the excessive bytes were written to FIFO before starting DMA transaction. The problem occurred when FIFO size were smaller than cache alignment, because writing all excessive bytes to FIFO would fail. It happened in DMA mode when PIO interrupts disabled, which caused driver hung. The solution is to test if buffer is alligned to cache line size before activating DMA mode, and if it's not, running PIO mode to align buffer and then starting DMA transaction. In PIO mode, when interrupts are enabled, lack of space in FIFO isn't the problem, so buffer aligning will always finish with success. Cc: # v3.18+ Reported-by: Krzysztof Kozlowski Signed-off-by: Robert Baldyga Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/samsung.c | 36 +++++++++++++++++++++--------------- 1 file changed, 21 insertions(+), 15 deletions(-) diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c index faee021c27b0..856686d6dcdb 100644 --- a/drivers/tty/serial/samsung.c +++ b/drivers/tty/serial/samsung.c @@ -294,15 +294,6 @@ static int s3c24xx_serial_start_tx_dma(struct s3c24xx_uart_port *ourport, if (ourport->tx_mode != S3C24XX_TX_DMA) enable_tx_dma(ourport); - while (xmit->tail & (dma_get_cache_alignment() - 1)) { - if (rd_regl(port, S3C2410_UFSTAT) & ourport->info->tx_fifofull) - return 0; - wr_regb(port, S3C2410_UTXH, xmit->buf[xmit->tail]); - xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1); - port->icount.tx++; - count--; - } - dma->tx_size = count & ~(dma_get_cache_alignment() - 1); dma->tx_transfer_addr = dma->tx_addr + xmit->tail; @@ -342,7 +333,8 @@ static void s3c24xx_serial_start_next_tx(struct s3c24xx_uart_port *ourport) } if (!ourport->dma || !ourport->dma->tx_chan || - count < ourport->min_dma_size) + count < ourport->min_dma_size || + xmit->tail & (dma_get_cache_alignment() - 1)) s3c24xx_serial_start_tx_pio(ourport); else s3c24xx_serial_start_tx_dma(ourport, count); @@ -736,7 +728,7 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id) struct uart_port *port = &ourport->port; struct circ_buf *xmit = &port->state->xmit; unsigned long flags; - int count; + int count, dma_count = 0; spin_lock_irqsave(&port->lock, flags); @@ -744,8 +736,12 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id) if (ourport->dma && ourport->dma->tx_chan && count >= ourport->min_dma_size) { - s3c24xx_serial_start_tx_dma(ourport, count); - goto out; + int align = dma_get_cache_alignment() - + (xmit->tail & (dma_get_cache_alignment() - 1)); + if (count-align >= ourport->min_dma_size) { + dma_count = count-align; + count = align; + } } if (port->x_char) { @@ -766,14 +762,24 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id) /* try and drain the buffer... */ - count = port->fifosize; - while (!uart_circ_empty(xmit) && count-- > 0) { + if (count > port->fifosize) { + count = port->fifosize; + dma_count = 0; + } + + while (!uart_circ_empty(xmit) && count > 0) { if (rd_regl(port, S3C2410_UFSTAT) & ourport->info->tx_fifofull) break; wr_regb(port, S3C2410_UTXH, xmit->buf[xmit->tail]); xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1); port->icount.tx++; + count--; + } + + if (!count && dma_count) { + s3c24xx_serial_start_tx_dma(ourport, dma_count); + goto out; } if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) { -- 2.20.1