Subject: Re: [PATCH 4/4] serial: 8250-mtk: modify uart DMA rx

From: Long Cheng <[email-masked]>
Date: Fri, 17 May 2019 15:36:42 +0800

On Wed, 2019-05-15 at 21:48 +0800, Nicolas Boichat wrote:
> On Sat, Apr 27, 2019 at 11:36 AM Long Cheng <[email-masked]> 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 <[email-masked]>
> > ---
> >  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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