Re: [PATCH v1 1/2] ARM: i.MX8MP: skov: add fallback for unsupported HW

[Sascha Hauer <s.hauer@pengutronix.de>]

On Mon, Mar 18, 2024 at 10:45:32AM +0100, Oleksij Rempel wrote:
> Add fallback support for currently not supported HW. Instead of
> completely fail, it is better to use some kind of basic devicetree with
> reduced functionality.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> ---
>  arch/arm/boards/skov-imx8mp/board.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/boards/skov-imx8mp/board.c b/arch/arm/boards/skov-imx8mp/board.c
> index 5424c3b9ab..a45fe8517f 100644
> --- a/arch/arm/boards/skov-imx8mp/board.c
> +++ b/arch/arm/boards/skov-imx8mp/board.c
> @@ -83,6 +83,12 @@ static const struct board_description imx8mp_variants[] = {
>  		.dts_compatible_hdmi = "skov,imx8mp-skov-revb-hdmi",
>  		.flags = SKOV_IMX8MP_HAS_HDMI,
>  	},
> +	/* Keep this entry always on the last place. It will be used
> +	 * as fallback variant if not supported variant is detected.
> +	 */
> +	{
> +		.dts_compatible = "skov,imx8mp-skov-basic",
> +	},

This increases ARRAY_SIZE(imx8mp_variants) to 3...
>  };
>  
>  static int skov_imx8mp_fixup(struct device_node *root, void *data)
> @@ -168,13 +174,14 @@ static int skov_imx8mp_init_variant(struct skov_imx8mp_priv *priv)
>  	if (ret)
>  		return ret;
>  
> -	priv->variant_id = v;
>  
>  	if (v >= ARRAY_SIZE(imx8mp_variants)) {

... so this doesn't trigger anymore for the still invalid variant 2.

Better make the basic variant a separate initializer outside of the
imx8mp_variants array. That also gets you rid of the "keep last" comment
above.

variant_id is written to the /chosen/skov,imx8mp-board-version property.
This looks wrong for the "basic" variant as this is not a fixed number
but instead depends on the highest number the bootloader knows (which
might be different from the last variant_id userspace knows).

> -		dev_err(dev, "Invalid variant %u\n", v);
> -		return -EINVAL;
> +		dev_warn(dev, "Unsuported variant %u. Fall back to basic variant\n", v);
> +		v = ARRAY_SIZE(imx8mp_variants) - 1;
>  	}

Sascha

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