[PATCH v2 17/32] mach-snapdragon: generate fdtfile automatically

[Neil Armstrong]

On 19/12/2023 17:04, Caleb Connolly wrote:
> With just a few basic rules, we can generate the $fdtfile environment
> variable to match the format used in Linux. This uses the root
> compatible property inside u-boot, with specific handling for the
> Dragonboard845c which is a special case, and for the qrb robotics
> boards.
> 
> This is known to work on supported platforms, and lets us avoid having a
> big lookup table.
> 
> Signed-off-by: Caleb Connolly <caleb.connolly at linaro.org>
> ---
>   arch/arm/mach-snapdragon/board.c | 101 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 101 insertions(+)
> 
> diff --git a/arch/arm/mach-snapdragon/board.c b/arch/arm/mach-snapdragon/board.c
> index b00f536d38b4..752166ea7563 100644
> --- a/arch/arm/mach-snapdragon/board.c
> +++ b/arch/arm/mach-snapdragon/board.c
> @@ -113,6 +113,106 @@ int board_init(void)
>   	return 0;
>   }
>   
> +/* Sets up the "board", and "soc" environment variables as well as constructing the devicetree
> + * path, with a few quirks to handle non-standard dtb filenames. This is not meant to be a
> + * comprehensive solution to automatically picking the DTB, but aims to be correct for the
> + * majority case. For most devices it should be possible to make this algorithm work by
> + * adjusting the root compatible property in the U-Boot DTS. Handling devices with multiple
> + * variants that are all supported by a single U-Boot image will require implementing device-
> + * specific detection.
> + */
> +static void configure_env(void)
> +{
> +	const char *first_compat, *last_compat;
> +	char *tmp;
> +	char buf[32] = { 0 };
> +	/*
> +	 * Most DTB filenames follow the scheme: qcom/<soc>-[vendor]-<board>.dtb
> +	 * The vendor is skipped when it's a Qualcomm reference board, or the
> +	 * db845c.
> +	 */
> +	char dt_path[64] = { 0 };
> +	int compat_count, ret;
> +	ofnode root;
> +
> +	root = ofnode_root();
> +	/* This is almost always 2, but be explicit that we want the first and last compatibles
> +	 * not the first and second.
> +	 */
> +	compat_count = ofnode_read_string_count(root, "compatible");
> +	if (compat_count < 2) {
> +		log_warning("%s: only one root compatible bailing!\n", __func__);
> +		return;
> +	}
> +
> +	/* The most specific device compatible (e.g. "thundercomm,db845c") */
> +	ret = ofnode_read_string_index(root, "compatible", 0, &first_compat);
> +	if (ret < 0) {
> +		log_warning("Can't read first compatible\n");
> +		return;
> +	}
> +
> +	/* The last compatible is always the SoC compatible */
> +	ret = ofnode_read_string_index(root, "compatible", compat_count - 1, &last_compat);
> +	if (ret < 0) {
> +		log_warning("Can't read second compatible\n");
> +		return;
> +	}
> +
> +	/* Copy the second compat (e.g. "qcom,sdm845") into buf */
> +	strlcpy(buf, last_compat, sizeof(buf) - 1);
> +	tmp = buf;
> +
> +	/* strsep() is destructive, it replaces the comma with a \0 */
> +	if (!strsep(&tmp, ",")) {
> +		log_warning("second compatible '%s' has no ','\n", buf);
> +		return;
> +	}
> +
> +	/* tmp now points to just the "sdm845" part of the string */
> +	env_set("soc", tmp);
> +
> +	/* Now figure out the "board" part from the first compatible */
> +	memset(buf, 0, sizeof(buf));
> +	strlcpy(buf, first_compat, sizeof(buf) - 1);
> +	tmp = buf;
> +
> +	/* The Qualcomm reference boards (RBx, HDK, etc)  */
> +	if (!strncmp("qcom", buf, strlen("qcom"))) {
> +		/*
> +		 * They all have the first compatible as "qcom,<soc>-<board>"
> +		 * (e.g. "qcom,qrb5165-rb5"). We extract just the part after
> +		 * the dash.
> +		 */
> +		if (!strsep(&tmp, "-")) {
> +			log_warning("compatible '%s' has no '-'\n", buf);
> +			return;
> +		}
> +		/* tmp is now "rb5" */
> +		env_set("board", tmp);
> +	} else {
> +		if (!strsep(&tmp, ",")) {
> +			log_warning("compatible '%s' has no ','\n", buf);
> +			return;
> +		}
> +		/* for thundercomm we just want the bit after the comma (e.g. "db845c"),
> +		 * for all other boards we replace the comma with a '-' and take both
> +		 * (e.g. "oneplus-enchilada")
> +		 */
> +		if (!strncmp("thundercomm", buf, strlen("thundercomm"))) {
> +			env_set("board", tmp);
> +		} else {
> +			*(tmp - 1) = '-';
> +			env_set("board", buf);
> +		}
> +	}
> +
> +	/* Now build the full path name */
> +	snprintf(dt_path, sizeof(dt_path), "qcom/%s-%s.dtb",
> +		 env_get("soc"), env_get("board"));
> +	env_set("fdtfile", dt_path);
> +}
> +
>   void __weak qcom_late_init(void)
>   {
>   }
> @@ -142,6 +242,7 @@ int board_late_init(void)
>   	if (status)
>   		log_warning("%s: Failed to set run time variables\n", __func__);
>   
> +	configure_env();
>   	qcom_late_init();
>   
>   	return 0;
> 

Nice, hope it will still fit for all future boards!


Reviewed-by: Neil Armstrong <neil.armstrong at linaro.org>