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SubjectRe: [PATCH 4/4] serial: 8250-mtk: modify uart DMA rx
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On Wed, 2019-05-15 at 21:48 +0800, Nicolas Boichat wrote:
> On Sat, Apr 27, 2019 at 11:36 AM Long Cheng <long.cheng@mediatek.com> wrote:
> >
> > Modify uart rx and complete for DMA.
>
> I don't know much about the DMA framework, but can you please explain
> why you are making the changes in this CL? I see that you are dropping
> dma_sync_single_for_device calls, for example, why?
>

the rx buffer is create by 'dma_alloc_coherent'. in the function, the
buffer is uncache. We don't need to sync between CPU and DMA. So I
remove it.

> >
> > Signed-off-by: Long Cheng <long.cheng@mediatek.com>
> > ---
> > drivers/tty/serial/8250/8250_mtk.c | 53 ++++++++++++++++--------------------
> > 1 file changed, 23 insertions(+), 30 deletions(-)
> >
> > diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
> > index c1fdbc0..04081a6 100644
> > --- a/drivers/tty/serial/8250/8250_mtk.c
> > +++ b/drivers/tty/serial/8250/8250_mtk.c
> > @@ -30,7 +30,6 @@
> > #define MTK_UART_DMA_EN_TX 0x2
> > #define MTK_UART_DMA_EN_RX 0x5
> >
> > -#define MTK_UART_TX_SIZE UART_XMIT_SIZE
> > #define MTK_UART_RX_SIZE 0x8000
> > #define MTK_UART_TX_TRIGGER 1
> > #define MTK_UART_RX_TRIGGER MTK_UART_RX_SIZE
> > @@ -64,28 +63,30 @@ static void mtk8250_dma_rx_complete(void *param)
> > struct mtk8250_data *data = up->port.private_data;
> > struct tty_port *tty_port = &up->port.state->port;
> > struct dma_tx_state state;
> > + int copied, cnt, tmp;
> > unsigned char *ptr;
> > - int copied;
> >
> > - dma_sync_single_for_cpu(dma->rxchan->device->dev, dma->rx_addr,
> > - dma->rx_size, DMA_FROM_DEVICE);
> > + if (data->rx_status == DMA_RX_SHUTDOWN)
> > + return;
> >
> > dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
> > + cnt = dma->rx_size - state.residue;
> > + tmp = cnt;
>
> I ponder, maybe we should rename cnt to left? (like, how many bytes
> are left to transfer, in total) Or maybe "total"
> Then maybe rename tmp to cnt.
>
like better.

> >
> > - if (data->rx_status == DMA_RX_SHUTDOWN)
> > - return;
> > + if ((data->rx_pos + cnt) > dma->rx_size)
> > + tmp = dma->rx_size - data->rx_pos;
>
> Maybe replace this and the line above:
> tmp = max_t(int, cnt, dma->rx_size - data->rx_pos);
>
Yes. It's better.

> >
> > - if ((data->rx_pos + state.residue) <= dma->rx_size) {
> > - ptr = (unsigned char *)(data->rx_pos + dma->rx_buf);
> > - copied = tty_insert_flip_string(tty_port, ptr, state.residue);
> > - } else {
> > - ptr = (unsigned char *)(data->rx_pos + dma->rx_buf);
> > - copied = tty_insert_flip_string(tty_port, ptr,
> > - dma->rx_size - data->rx_pos);
> > + ptr = (unsigned char *)(data->rx_pos + dma->rx_buf);
> > + copied = tty_insert_flip_string(tty_port, ptr, tmp);
> > + data->rx_pos += tmp;
> > +
> > + if (cnt > tmp) {
> > ptr = (unsigned char *)(dma->rx_buf);
> > - copied += tty_insert_flip_string(tty_port, ptr,
> > - data->rx_pos + state.residue - dma->rx_size);
> > + tmp = cnt - tmp;
> > + copied += tty_insert_flip_string(tty_port, ptr, tmp);
> > + data->rx_pos = tmp;
> > }
> > +
> > up->port.icount.rx += copied;
> >
> > tty_flip_buffer_push(tty_port);
> > @@ -96,9 +97,7 @@ static void mtk8250_dma_rx_complete(void *param)
> > static void mtk8250_rx_dma(struct uart_8250_port *up)
> > {
> > struct uart_8250_dma *dma = up->dma;
> > - struct mtk8250_data *data = up->port.private_data;
> > struct dma_async_tx_descriptor *desc;
> > - struct dma_tx_state state;
> >
> > desc = dmaengine_prep_slave_single(dma->rxchan, dma->rx_addr,
> > dma->rx_size, DMA_DEV_TO_MEM,
> > @@ -113,12 +112,6 @@ static void mtk8250_rx_dma(struct uart_8250_port *up)
> >
> > dma->rx_cookie = dmaengine_submit(desc);
> >
> > - dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
> > - data->rx_pos = state.residue;
> > -
> > - dma_sync_single_for_device(dma->rxchan->device->dev, dma->rx_addr,
> > - dma->rx_size, DMA_FROM_DEVICE);
> > -
> > dma_async_issue_pending(dma->rxchan);
> > }
> >
> > @@ -131,13 +124,13 @@ static void mtk8250_dma_enable(struct uart_8250_port *up)
> > if (data->rx_status != DMA_RX_START)
> > return;
> >
> > - dma->rxconf.direction = DMA_DEV_TO_MEM;
> > - dma->rxconf.src_addr_width = dma->rx_size / 1024;
> > - dma->rxconf.src_addr = dma->rx_addr;
> > + dma->rxconf.direction = DMA_DEV_TO_MEM;
> > + dma->rxconf.src_port_window_size = dma->rx_size;
> > + dma->rxconf.src_addr = dma->rx_addr;
> >
> > - dma->txconf.direction = DMA_MEM_TO_DEV;
> > - dma->txconf.dst_addr_width = MTK_UART_TX_SIZE / 1024;
> > - dma->txconf.dst_addr = dma->tx_addr;
> > + dma->txconf.direction = DMA_MEM_TO_DEV;
> > + dma->txconf.dst_port_window_size = UART_XMIT_SIZE;
> > + dma->txconf.dst_addr = dma->tx_addr;
> >
> > serial_out(up, UART_FCR, UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_RCVR |
> > UART_FCR_CLEAR_XMIT);
> > @@ -217,7 +210,7 @@ static void mtk8250_shutdown(struct uart_port *port)
> > * Mediatek UARTs use an extra highspeed register (UART_MTK_HIGHS)
> > *
> > * We need to recalcualte the quot register, as the claculation depends
> > - * on the vaule in the highspeed register.
> > + * on the value in the highspeed register.
>
> Since you're doing some cosmetic changes here, you might as well fix
> recalcualte => recalculate and claculation => calculation on the line
> above.
>

I see.

> But technically, this should belong in another patch...
>
> > *
> > * Some baudrates are not supported by the chip, so we use the next
> > * lower rate supported and update termios c_flag.
> > --
> > 1.7.9.5
> >


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