Re: [PATCH v3 06/15] Introduce structured tag value definition

[Herve Codina <herve.codina@bootlin.com>]

Hi david,

On Thu, 10 Sep 2026 15:33:58 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Aug 26, 2026 at 10:31:37AM +0200, Herve Codina wrote:
> [snip]
> > +#define FDT_TAG_CAN_SKIP(tag_data, tag_id) \
> > +		(FDT_TAG_STRUCTURED | FDT_TAG_SKIP_SAFE | tag_data | tag_id)
> > +
> > +/* Tests reserved tags */
> > +#define FDT_TEST_NONE_CAN_SKIP		FDT_TAG_CAN_SKIP(FDT_TAG_DATA_NONE, 0)
> > +#define FDT_TEST_1CELL_CAN_SKIP		FDT_TAG_CAN_SKIP(FDT_TAG_DATA_1CELL, 0)
> > +#define FDT_TEST_2CELLS_CAN_SKIP	FDT_TAG_CAN_SKIP(FDT_TAG_DATA_2CELLS, 0)
> > +#define FDT_TEST_VARLEN_CAN_SKIP	FDT_TAG_CAN_SKIP(FDT_TAG_DATA_VARLEN, 0)
> > +#define FDT_TEST_NONE_NO_SKIP		FDT_TAG_NO_SKIP(FDT_TAG_DATA_NONE, 0)  
> 
> Sorry, missed until I saw the later treegen changes that this is
> defining some specific tag values.
> 
> Given that, "Tests reserved tags" needs to be expanded to better
> explain what these tags are for - what should readers do upon
> encountering them, when should writers use it ("never, unless you're a
> test case" is acceptable).

I would say, in both cases, consider them as "unknown" tags.
And so:
/*
 * Tests reserved tags
 * 
 * When those tags are encountered they should be considered as "unknown"
 * tags and rules related to "unknown" tags must be followed.
 *
 * Readers should skip them or fail depending on the SKIP_SAFE flag. Writers
 * should never use those tags. Their usage is only acceptable in test cases.
 */

> 
> It might be worth reserving a whole range of tag values for tests /
> documentation / experimentation, rather than just a handful of
> specific values.
> 

Ok. The range reservation will added be in the comment.

/*
 * Tests reserved tags
 *
 * A TAG_ID range in "structured tags" is reserved to tests tags.
 * This tests reserved range is from tag_id 0 to tag_id 0x100.
 *
 * When those tags are encountered they should be considered as "unknown"
 * tags and rules related to "unknown" tags must be followed.
 *
 * Readers should skip them or fail depending on the SKIP_SAFE flag. Writers
 * should never use those tags. Their usage is only acceptable in test cases.
 */

Is it ok?

Best regards,
Hervé


-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com