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

[David Gibson]

On Thu, Sep 10, 2026 at 09:58:23AM +0200, Herve Codina wrote:
> Hi david,
> 
> On Thu, 10 Sep 2026 15:33:58 +1000
> David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> 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?

I'd probably put the reserved range up high somewhere rather than
starting at 0.  Otherwise it looks good.


-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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