Re: [PATCH v1 1/8] i2c: Introduce i2c_10bit_addr_from_msg()

[Geert Uytterhoeven]

Hi Andy,

On Wed, 12 Feb 2025 at 17:35, Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> There are already a lot of drivers that have been using
> i2c_8bit_addr_from_msg() for 7-bit addresses, now it's time
> to have the similar for 10-bit addresses.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

Thanks for your patch!

> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -952,6 +952,16 @@ static inline u8 i2c_8bit_addr_from_msg(const struct i2c_msg *msg)
>         return (msg->addr << 1) | (msg->flags & I2C_M_RD);
>  }
>
> +static inline u8 i2c_10bit_addr_from_msg(const struct i2c_msg *msg)

Having never used 10-bit addressing myself, or even looked into it,
it took me a while to understand what this helper really does...
So this returns the high byte of the artificial 16-bit address that
must be used to address a target that uses 10-bit addressing?
Hence I think this should be renamed, to better match its purpose.

> +{
> +       /*
> +        * 10-bit address
> +        *   addr_1: 5'b11110 | addr[9:8] | (R/nW)
> +        *   addr_2: addr[7:0]

I think the second comment line does not belong here, as this function
doesn't care about that part.

> +        */
> +       return 0xf0 | ((msg->addr & GENMASK(9, 8)) >> 7) | (msg->flags & I2C_M_RD);
> +}

Probably you also want to add a similar but much simpler helper to
return the low byte?

> +
>  u8 *i2c_get_dma_safe_msg_buf(struct i2c_msg *msg, unsigned int threshold);
>  void i2c_put_dma_safe_msg_buf(u8 *buf, struct i2c_msg *msg, bool xferred);
>

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds