Re: [PATCH v2 06/15] ARM: i.MX: scratch: add FDT support

[Marco Felsch <m.felsch@pengutronix.de>]

On 26-02-06, Ahmad Fatoum wrote:
> 
> 
> On 2/4/26 9:01 PM, Marco Felsch wrote:
> > Add support to store a FDT within the scratch area. The user needs to
> > query the location and size via imx_scratch_get_fdt() which can be used
> > afterwards to write the actual FDT into it.
> > 
> > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > ---
> >  arch/arm/mach-imx/scratch.c | 24 ++++++++++++++++++++++++
> >  common/Kconfig              | 14 ++++++++++++++
> >  include/mach/imx/scratch.h  |  2 ++
> >  3 files changed, 40 insertions(+)
> > 
> > diff --git a/arch/arm/mach-imx/scratch.c b/arch/arm/mach-imx/scratch.c
> > index e4e2d25969f061c9fcdfd7c3d87701b715eb2805..da138445dfb352f2f3497be77004aefc7d46f188 100644
> > --- a/arch/arm/mach-imx/scratch.c
> > +++ b/arch/arm/mach-imx/scratch.c
> > @@ -16,7 +16,10 @@ struct imx_scratch_space {
> >  	u32 bootrom_log[128];
> >  	u32 reserved[128];		/* reserve for bootrom log */
> >  	struct optee_header optee_hdr;
> > +	/* FDT needs an 8 byte alignment */
> > +	u8 fdt[CONFIG_SCRATCH_FDT_SIZE] __aligned(8);
> >  };
> > +static_assert(sizeof(struct imx_scratch_space) <= CONFIG_SCRATCH_SIZE);
> >  
> >  static struct imx_scratch_space *scratch;
> >  
> > @@ -92,3 +95,24 @@ const struct optee_header *imx_scratch_get_optee_hdr(void)
> >  
> >  	return &scratch->optee_hdr;
> >  }
> > +
> > +u8 *imx_scratch_get_fdt(unsigned int *fdt_sz)
> > +{
> > +	unsigned int sz;
> > +
> > +	if (!scratch) {
> > +		if (IN_PBL)
> > +			return ERR_PTR(-EINVAL);
> > +		else
> > +			scratch = (void *)arm_mem_scratch_get();
> > +	}
> > +
> > +	sz = sizeof(scratch->fdt);
> > +	if (sz == 0)
> > +		return NULL;
> > +
> > +	if (fdt_sz)
> > +		*fdt_sz = sz;
> > +
> > +	return scratch->fdt;
> > +}
> > diff --git a/common/Kconfig b/common/Kconfig
> > index 50c26695b2b56a943edfd00a7e0cb1067ad269a9..265652900a5632177d36efa84d590be6db2e7015 100644
> > --- a/common/Kconfig
> > +++ b/common/Kconfig
> > @@ -304,6 +304,20 @@ config SCRATCH_SIZE
> >  	default 0x8000
> >  	prompt "Scratch size"
> >  
> > +config SCRATCH_FDT_SIZE
> > +	hex
> > +	default 0x0
> > +	prompt "Scratch FDT size"
> > +	help
> > +	  The size of the scratch area used as destination to load and optional
> > +	  decompress the barebox builtin DTB into it. Can be 0x0 if early FDT
> > +	  support is not requied.
> > +
> > +	  If specified, SCRATCH_FDT_SIZE <= SCRATCH_SIZE must be ensured.
> > +
> > +	  This option should match the OP-TEE's CFG_DTB_MAX_SIZE configuration
> > +	  if used by OP-TEE.
> 
> AFAIU, this is a workaround because OP-TEE doesn't accept outside
> information about how big the DTB buffer is, just its base address.

This is correct for the bl_params case. In case of transfer-lists the
size could be detected by OP-TEE OS.

> In that case, this should go to security/Kconfig and be named something
> like PBL_OPTEE_DTB_MAX_SIZE. There's no need to ask every user that
> configures barebox about this.

This would bind the FDT support to OP-TEE but the FDT could be used by
other boot binaries as well. In the speak of ARM, it could be used by
the TF-A. In the speak of RISC-V, it could be used by opensbi. Therefore
I made it generic.

I wanted to avoid multiple Kconfig options to configure the scatch space
for:
 - OP-TEE FDT
 - OpenSBI FDT
 - TF-A FDT

I'm currently unsure if dropping the OP-TEE note from the help message
helps. But I have no hard feelings about PBL_OPTEE_DTB_MAX_SIZE either.

Regards,
  Marco


> 
> 
> Cheers,
> Ahmad
> 
> -- 
> Pengutronix e.K.                  |                             |
> Steuerwalder Str. 21              | http://www.pengutronix.de/  |
> 31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |
> 
> 

-- 
#gernperDu 
#CallMeByMyFirstName

Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | https://www.pengutronix.de/ |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-9    |