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Date:   Wed, 22 May 2019 13:24:22 +0800
From:   Long Cheng <long.cheng@...iatek.com>
To:     Nicolas Boichat <drinkcat@...omium.org>
CC:     Vinod Koul <vkoul@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Ryder Lee" <ryder.lee@...iatek.com>,
        Sean Wang <sean.wang@...nel.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sean Wang <sean.wang@...iatek.com>,
        <dmaengine@...r.kernel.org>, <devicetree@...r.kernel.org>,
        "linux-arm Mailing List" <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        <linux-serial@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Yingjoe Chen <yingjoe.chen@...iatek.com>,
        YT Shen <yt.shen@...iatek.com>,
        Zhenbao Liu <zhenbao.liu@...iatek.com>,
        Long Cheng <long.cheng@...iatek.com>
Subject: Re: [PATCH 4/4] serial: 8250-mtk: modify uart DMA rx

On Fri, 2019-05-17 at 15:36 +0800, Long Cheng wrote:
> 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@...iatek.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@...iatek.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.
> 

can't replace by 'max_t'. So I will keep original code.

> > >
> > > -       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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