[PATCH RESEND 12/16] mach-snapdragon: parse incoming ARM32 ATAGS

[Sam Day]

Heya Casey,

On Wednesday, 3 June 2026 at 11:47 PM, Casey Connolly <casey.connolly at linaro.org> wrote:

> Hi Sam,
> 
> (CC list definitely needs some tuning on the next revision XD)

Hmm? Is it incorrect to use `b4 prep --auto-to-cc` nowadays?

> 
> On 6/1/26 10:12, Sam Day via B4 Relay wrote:
> > From: Sam Day <me at samcday.com>
> >
> > Many (often fused) bootloaders on older ARMv7 qcom SoCs do not support
> > FDTs at all, and instead pass along ATAGS in r2.
> >
> > Minimal support for parsing memory info out of these tags is introduced,
> > so that we can support mainline devicetrees, which expect the bootloader
> > to populate /memory nodes.
> 
> I think this should go its own armv7-specific file. It would probably
> also make sense to just have a separate implementation of
> board_fdt_blob_setup() since it's already really quite complicated.

I was considering that as well but decided against it, since sprinkling #ifdef
everywhere is quite ugly, and the ATAGS handling code is quite minimal. Are you
sure it really needs to be split out?

> 
> The SMEM series will do a bit of rework, in the next spin I'll probably
> move the caching stuff out as well, maybe I should also take
> board_fdt_blob_setup() then the file can be arm64 specific?

I'm not sure how we can have a separate version of board_fdt_blob_setup. On
ARMv7, sometimes you'll br receiving ATAGS in r2, sometimes it'll be FDT. It
depends on which bootloader you're chaining from.

e.g my nokia-fame can run U-Boot directly chained from SBL3 since the bootchain
on this device has been broken enough, in which case U-Boot gets ATAGS. My
samsung-expressltexx chains from lk2nd, in which case U-Boot gets an FDT.

Cheers,
-Sam

> 
> >
> > Signed-off-by: Sam Day <me at samcday.com>
> > ---
> >   arch/arm/mach-snapdragon/board.c | 119 ++++++++++++++++++++++++++++++---------
> >   1 file changed, 91 insertions(+), 28 deletions(-)
> >
> > diff --git a/arch/arm/mach-snapdragon/board.c b/arch/arm/mach-snapdragon/board.c
> > index 627b566d178..753983467a0 100644
> > --- a/arch/arm/mach-snapdragon/board.c
> > +++ b/arch/arm/mach-snapdragon/board.c
> > @@ -11,6 +11,7 @@
> >
> >   #include <asm/gpio.h>
> >   #include <asm/io.h>
> > +#include <asm/setup.h>
> >   #include <asm/system.h>
> >   #include <dm/device.h>
> >   #include <dm/pinctrl.h>
> > @@ -175,6 +176,67 @@ static int qcom_parse_memory(const void *fdt)
> >   	return 0;
> >   }
> >
> > +static bool qcom_atags_valid(const phys_addr_t p)
> > +{
> > +	const struct tag *tags = (const struct tag *)p;
> > +
> > +	return tags && tags->hdr.tag == ATAG_CORE &&
> > +	       tags->hdr.size >= sizeof(struct tag_header) / sizeof(u32);
> > +}
> > +
> > +static int qcom_parse_atags(const struct tag *tags)
> > +{
> > +	phys_addr_t ram_end = 0;
> > +	const struct tag *t;
> > +	bool atags_end = false;
> > +	u32 words = 0;
> > +	int j = 0;
> > +
> > +	memset(prevbl_ddr_banks, 0, sizeof(prevbl_ddr_banks));
> > +
> > +	for (t = tags; words < SZ_16K / sizeof(u32); t = tag_next(t)) {
> > +		if (t->hdr.tag == ATAG_NONE) {
> > +			atags_end = true;
> > +			break;
> > +		}
> > +		if (t->hdr.size < sizeof(struct tag_header) / sizeof(u32))
> > +			return -EINVAL;
> > +		if (t->hdr.size > SZ_16K / sizeof(u32) - words)
> > +			return -EINVAL;
> > +
> > +		words += t->hdr.size;
> > +
> > +		if (t->hdr.tag != ATAG_MEM)
> > +			continue;
> > +		if (t->hdr.size < tag_size(tag_mem32))
> > +			return -EINVAL;
> > +		if (!t->u.mem.size)
> > +			continue;
> > +
> > +		prevbl_ddr_banks[j].start = t->u.mem.start;
> > +		prevbl_ddr_banks[j].size = t->u.mem.size;
> > +		ram_end = max(ram_end, (phys_addr_t)t->u.mem.start + t->u.mem.size);
> > +		j++;
> > +
> > +		if (j == CONFIG_NR_DRAM_BANKS)
> > +			break;
> > +	}
> > +
> > +	if (!atags_end && j < CONFIG_NR_DRAM_BANKS) {
> > +		log_err("Provided more memory banks than we can handle\n");
> > +		return -EINVAL;
> > +	}
> > +	if (!j)
> > +		return -ENODATA;
> > +
> > +	qsort(prevbl_ddr_banks, j, sizeof(prevbl_ddr_banks[0]), ddr_bank_cmp);
> > +
> > +	gd->ram_base = prevbl_ddr_banks[0].start;
> > +	gd->ram_size = ram_end - gd->ram_base;
> > +
> > +	return 0;
> > +}
> > +
> >   static void show_psci_version(void)
> >   {
> >   #ifdef CONFIG_ARM64
> > @@ -227,42 +289,52 @@ static void qcom_psci_fixup(void *fdt)
> >    */
> >   int board_fdt_blob_setup(void **fdtp)
> >   {
> > -	struct fdt_header *external_fdt, *internal_fdt;
> > -	bool internal_valid, external_valid;
> > -	int ret = -ENODATA;
> > -
> > -	internal_fdt = (struct fdt_header *)*fdtp;
> > -	external_fdt = (struct fdt_header *)get_prev_bl_fdt_addr();
> > -	external_valid = external_fdt && !fdt_check_header(external_fdt);
> > -	internal_valid = !fdt_check_header(internal_fdt);
> > +	int ret = -ENODATA, setup_ret = -EEXIST;
> > +	struct fdt_header *internal_fdt = *fdtp;
> > +	phys_addr_t prev_bl_arg = get_prev_bl_fdt_addr();
> > +	bool internal_valid = internal_fdt && !fdt_check_header(internal_fdt);
> > +	bool external_is_fdt = prev_bl_arg &&
> > +			       !fdt_check_header((const void *)prev_bl_arg);
> >
> > -	/*
> > -	 * There is no point returning an error here, U-Boot can't do anything useful in this situation.
> > -	 * Bail out while we can still print a useful error message.
> > -	 */
> > -	if (!internal_valid && !external_valid)
> > +	if (internal_valid) {
> > +		debug("Using built in FDT\n");
> > +	} else if (external_is_fdt) {
> > +		debug("Using external FDT\n");
> > +		*fdtp = (void *)prev_bl_arg;
> > +		setup_ret = 0;
> > +	} else {
> > +		/*
> > +		 * There is no point returning an error here, U-Boot can't do
> > +		 * anything useful in this situation. Bail out while we can
> > +		 * still print a useful error message.
> > +		 */
> >   		panic("Internal FDT is invalid and no external FDT was provided! (fdt=%p)\n",
> > -		      external_fdt);
> > +		      (void *)prev_bl_arg);
> > +	}
> >
> >   	/* Prefer memory information from internal DT if it's present */
> >   	if (internal_valid)
> >   		ret = qcom_parse_memory(internal_fdt);
> >
> > -	if (ret < 0 && external_valid) {
> > +	if (ret < 0 && prev_bl_arg) {
> >   		/* No internal FDT or it lacks a proper /memory node.
> >   		 * The previous bootloader handed us something, let's try that.
> >   		 */
> >   		if (internal_valid)
> >   			debug("No memory info in internal FDT, falling back to external\n");
> >
> > -		ret = qcom_parse_memory(external_fdt);
> > +		/* the prev BL arg is either an FDT or ATAGS */
> > +		if (external_is_fdt)
> > +			ret = qcom_parse_memory((const void *)prev_bl_arg);
> > +		if (ret < 0 && qcom_atags_valid(prev_bl_arg))
> > +			ret = qcom_parse_atags((const struct tag *)prev_bl_arg);
> >   	}
> >
> >   	if (ret < 0)
> >   		panic("No valid memory ranges found!\n");
> >
> > -	/* If we have an external FDT, it can only have come from the Android bootloader. */
> > -	if (external_valid)
> > +	/* If we have a prev BL arg, we assume it came from ABL */
> > +	if (prev_bl_arg)
> >   		qcom_boot_source = QCOM_BOOT_SOURCE_ANDROID;
> >   	else
> >   		qcom_boot_source = QCOM_BOOT_SOURCE_XBL;
> > @@ -270,18 +342,9 @@ int board_fdt_blob_setup(void **fdtp)
> >   	debug("ram_base = %#011lx, ram_size = %#011llx\n",
> >   	      gd->ram_base, (unsigned long long)gd->ram_size);
> >
> > -	if (internal_valid) {
> > -		debug("Using built in FDT\n");
> > -		ret = -EEXIST;
> > -	} else {
> > -		debug("Using external FDT\n");
> > -		*fdtp = external_fdt;
> > -		ret = 0;
> > -	}
> > -
> >   	qcom_psci_fixup(*fdtp);
> >
> > -	return ret;
> > +	return setup_ret;
> >   }
> >
> >   /*
> >
> 
>