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From:   Tim Harvey <tharvey@gateworks.com>
Date:   Tue, 30 Jun 2020 10:11:33 -0700
Message-ID: <CAJ+vNU1sEqo4ty68-9LeKFd4oY-qKiEt7_unp-1oCjX=+XQr7g@mail.gmail.com>
Subject: Re: [PATCH] can: mcp251x: add support for half duplex controllers
To:     Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        linux-can@vger.kernel.org, netdev <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Cc:     "David S . Miller" <davem@davemloft.net>,
        Sean Nyekjaer <sean@geanix.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        =?UTF-8?B?VGltbyBTY2hsw7zDn2xlcg==?= <schluessler@krause.de>,
        "Gustavo A . R . Silva" <gustavo@embeddedor.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Thu, May 28, 2020 at 8:28 AM Tim Harvey <tharvey@gateworks.com> wrote:
>
> Some SPI host controllers do not support full-duplex SPI and are
> marked as such via the SPI_CONTROLLER_HALF_DUPLEX controller flag.
>
> For such controllers use half duplex transactions but retain full
> duplex transactions for the controllers that can handle those.
>
> Signed-off-by: Tim Harvey <tharvey@gateworks.com>
> ---
>  drivers/net/can/spi/mcp251x.c | 34 +++++++++++++++++++++++++++-------
>  1 file changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/can/spi/mcp251x.c b/drivers/net/can/spi/mcp251x.c
> index 5009ff2..203ef20 100644
> --- a/drivers/net/can/spi/mcp251x.c
> +++ b/drivers/net/can/spi/mcp251x.c
> @@ -290,8 +290,12 @@ static u8 mcp251x_read_reg(struct spi_device *spi, u8 reg)
>         priv->spi_tx_buf[0] = INSTRUCTION_READ;
>         priv->spi_tx_buf[1] = reg;
>
> -       mcp251x_spi_trans(spi, 3);
> -       val = priv->spi_rx_buf[2];
> +       if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
> +               spi_write_then_read(spi, priv->spi_tx_buf, 2, &val, 1);
> +       } else {
> +               mcp251x_spi_trans(spi, 3);
> +               val = priv->spi_rx_buf[2];
> +       }
>
>         return val;
>  }
> @@ -303,10 +307,18 @@ static void mcp251x_read_2regs(struct spi_device *spi, u8 reg, u8 *v1, u8 *v2)
>         priv->spi_tx_buf[0] = INSTRUCTION_READ;
>         priv->spi_tx_buf[1] = reg;
>
> -       mcp251x_spi_trans(spi, 4);
> +       if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
> +               u8 val[2] = { 0 };
>
> -       *v1 = priv->spi_rx_buf[2];
> -       *v2 = priv->spi_rx_buf[3];
> +               spi_write_then_read(spi, priv->spi_tx_buf, 2, val, 2);
> +               *v1 = val[0];
> +               *v2 = val[1];
> +       } else {
> +               mcp251x_spi_trans(spi, 4);
> +
> +               *v1 = priv->spi_rx_buf[2];
> +               *v2 = priv->spi_rx_buf[3];
> +       }
>  }
>
>  static void mcp251x_write_reg(struct spi_device *spi, u8 reg, u8 val)
> @@ -409,8 +421,16 @@ static void mcp251x_hw_rx_frame(struct spi_device *spi, u8 *buf,
>                         buf[i] = mcp251x_read_reg(spi, RXBCTRL(buf_idx) + i);
>         } else {
>                 priv->spi_tx_buf[RXBCTRL_OFF] = INSTRUCTION_READ_RXB(buf_idx);
> -               mcp251x_spi_trans(spi, SPI_TRANSFER_BUF_LEN);
> -               memcpy(buf, priv->spi_rx_buf, SPI_TRANSFER_BUF_LEN);
> +               if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
> +                       spi_write_then_read(spi, priv->spi_tx_buf, 1,
> +                                           priv->spi_rx_buf,
> +                                           SPI_TRANSFER_BUF_LEN);
> +                       memcpy(buf + 1, priv->spi_rx_buf,
> +                              SPI_TRANSFER_BUF_LEN - 1);
> +               } else {
> +                       mcp251x_spi_trans(spi, SPI_TRANSFER_BUF_LEN);
> +                       memcpy(buf, priv->spi_rx_buf, SPI_TRANSFER_BUF_LEN);
> +               }
>         }
>  }
>
> --
> 2.7.4
>

Marc / Wolfgang,

Any feedback on this?

Best Regards,

Tim