netdev - Re: [PATCH net-next] net: dsa: xrs700x: Correctly address device over I2C

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Date:   Tue, 2 Feb 2021 14:05:20 -0600
From:   George McCollister <george.mccollister@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: xrs700x: Correctly address device over I2C

On Tue, Feb 2, 2021 at 1:17 PM Tobias Waldekranz <tobias@...dekranz.com> wrote:
[snip]
>
> George, have you used the chip in I2C mode with the code that is on
> net-next now? I was not able to get the driver to even read the ID
> register correctly.

I wrote the i2c driver before I had any hardware in hand thinking I
was going to get a board with the switch connected via i2c. When the
board arrived it turned out it was connected via mdio so I wrote that
driver as well. I looked it over quite carefully but I guess the
documentation was wrong and I had the register addresses shifted off
by one. I never ended up with hardware to test the i2c.

>
>  drivers/net/dsa/xrs700x/xrs700x_i2c.c | 31 ++++++++++++---------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/net/dsa/xrs700x/xrs700x_i2c.c b/drivers/net/dsa/xrs700x/xrs700x_i2c.c
> index a5f8883af829..16a46a78a037 100644
> --- a/drivers/net/dsa/xrs700x/xrs700x_i2c.c
> +++ b/drivers/net/dsa/xrs700x/xrs700x_i2c.c
> @@ -10,33 +10,34 @@
>  #include "xrs700x.h"
>  #include "xrs700x_reg.h"
>
> +struct xrs700x_i2c_cmd {
> +       __be32 reg;
> +       __be16 val;
> +} __packed;
> +
>  static int xrs700x_i2c_reg_read(void *context, unsigned int reg,
>                                 unsigned int *val)
>  {
>         struct device *dev = context;
>         struct i2c_client *i2c = to_i2c_client(dev);
> -       unsigned char buf[4];
> +       struct xrs700x_i2c_cmd cmd;
>         int ret;
>
> -       buf[0] = reg >> 23 & 0xff;
> -       buf[1] = reg >> 15 & 0xff;
> -       buf[2] = reg >> 7 & 0xff;
> -       buf[3] = (reg & 0x7f) << 1;
> +       cmd.reg = cpu_to_be32(reg | 1);
>
> -       ret = i2c_master_send(i2c, buf, sizeof(buf));
> +       ret = i2c_master_send(i2c, (char *)&cmd.reg, sizeof(cmd.reg));
>         if (ret < 0) {
>                 dev_err(dev, "xrs i2c_master_send returned %d\n", ret);
>                 return ret;
>         }
>
> -       ret = i2c_master_recv(i2c, buf, 2);
> +       ret = i2c_master_recv(i2c, (char *)&cmd.val, sizeof(cmd.val));
>         if (ret < 0) {
>                 dev_err(dev, "xrs i2c_master_recv returned %d\n", ret);
>                 return ret;
>         }
>
> -       *val = buf[0] << 8 | buf[1];
> -
> +       *val = be16_to_cpu(cmd.val);
>         return 0;
>  }
>
> @@ -45,17 +46,13 @@ static int xrs700x_i2c_reg_write(void *context, unsigned int reg,
>  {
>         struct device *dev = context;
>         struct i2c_client *i2c = to_i2c_client(dev);
> -       unsigned char buf[6];
> +       struct xrs700x_i2c_cmd cmd;
>         int ret;
>
> -       buf[0] = reg >> 23 & 0xff;
> -       buf[1] = reg >> 15 & 0xff;
> -       buf[2] = reg >> 7 & 0xff;
> -       buf[3] = (reg & 0x7f) << 1 | 1;
> -       buf[4] = val >> 8 & 0xff;
> -       buf[5] = val & 0xff;
> +       cmd.reg = cpu_to_be32(reg);
> +       cmd.val = cpu_to_be16(val);
>
> -       ret = i2c_master_send(i2c, buf, sizeof(buf));
> +       ret = i2c_master_send(i2c, (char *)&cmd, sizeof(cmd));
>         if (ret < 0) {
>                 dev_err(dev, "xrs i2c_master_send returned %d\n", ret);
>                 return ret;
> --
> 2.17.1
>

Reviewed-by: George McCollister <george.mccollister@...il.com>