Re: [PATCH RFT 1/2] i2c: rcar: reset controller is mandatory for Gen3+

[Geert Uytterhoeven]

Hi Wolfram,

Thanks for your patch!
On Wed, Sep 13, 2023 at 8:41 AM Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
> Initially, we only needed a reset controller to make sure RXDMA works at
> least once per transfer. Meanwhile, documentation has been updated. It
> now says that a reset has to be performed prior every transaction, also
> if it is non-DMA. So, make the reset controller a requirement instead of
> being optional.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

> --- a/drivers/i2c/busses/i2c-rcar.c
> +++ b/drivers/i2c/busses/i2c-rcar.c
> @@ -838,12 +838,10 @@ static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
>
>         /* Gen3 needs a reset before allowing RXDMA once */
>         if (priv->devtype == I2C_RCAR_GEN3) {
> -               priv->flags |= ID_P_NO_RXDMA;
> -               if (!IS_ERR(priv->rstc)) {
> -                       ret = rcar_i2c_do_reset(priv);
> -                       if (ret == 0)
> -                               priv->flags &= ~ID_P_NO_RXDMA;
> -               }
> +               priv->flags &= ~ID_P_NO_RXDMA;
> +               ret = rcar_i2c_do_reset(priv);
> +               if (ret)
> +                       priv->flags |= ID_P_NO_RXDMA;

This is pre-existing, but if rcar_i2c_do_reset() returns an error,
that means the I2C block couldn't get out of reset.  Are we sure we
can still do PIO transfers in that case, or should this be considered
a fatal error?

>         }
>
>         rcar_i2c_init(priv);
> @@ -1096,11 +1094,13 @@ static int rcar_i2c_probe(struct platform_device *pdev)
>
>         if (priv->devtype == I2C_RCAR_GEN3) {
>                 priv->rstc = devm_reset_control_get_exclusive(&pdev->dev, NULL);
> -               if (!IS_ERR(priv->rstc)) {
> -                       ret = reset_control_status(priv->rstc);
> -                       if (ret < 0)
> -                               priv->rstc = ERR_PTR(-ENOTSUPP);
> -               }
> +               if (IS_ERR(priv->rstc))
> +                       return dev_err_probe(&pdev->dev, PTR_ERR(priv->rstc),
> +                                            "couldn't get reset");
> +
> +               ret = reset_control_status(priv->rstc);
> +               if (ret < 0)
> +                       return ret;

This is a pre-existing check, but do you really need it?
This condition will be true if the reset is still asserted, which
could happen due to some glitch, or force-booting into a new kernel
using kexec.  And AFAIUI, that should be resolved by the call to
rcar_i2c_do_reset() above.

>         }
>
>         /* Stay always active when multi-master to keep arbitration working */

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