Re: [PATCH 2/4] cxl: Add KUnit tests for HDM decoder encoding helpers

[Alison Schofield <alison.schofield@intel.com>]

On Fri, Oct 16, 2026 at 09:01:37PM +0100, Jonathan Cameron wrote:
> On Tue, 13 Oct 2026 21:17:53 -0700
> Alison Schofield <alison.schofield@intel.com> wrote:
> 
> > The CXL subsystem has no KUnit infrastructure for testing self-contained
> > logic.
> > 
> > Introduce CONFIG_CXL_KUNIT_TEST and drivers/cxl/.kunitconfig, along with
> > an initial suite for the HDM decoder interleave encoding helpers. The
> > suite checks valid and invalid encodings and round-trip conversions.
> > 
> > Use a single Kconfig option for all CXL KUnit suites, with each suite
> > built as a separate module. This allows new suites to be added without
> > requiring additional configuration options.
> > 
> > The HDM decoder helpers provide a starting point for establishing the
> > location, naming, and configuration conventions for future CXL KUnit tests.
> > 
> > Suggested-by: Dave Jiang <dave.jiang@intel.com>
> > Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> 
> Just one thing inline for the only case where the test is exhaustive.
> Either way on that
> Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
> 
> > diff --git a/drivers/cxl/tests/hdm_encoding_kunit.c b/drivers/cxl/tests/hdm_encoding_kunit.c
> > new file mode 100644
> > index 000000000000..54a7cb078a06
> > --- /dev/null
> > +++ b/drivers/cxl/tests/hdm_encoding_kunit.c
> 
> > +
> > +/* Decoder Count field of the CXL HDM Decoder Capability Register */
> > +static void hdm_decoder_count(struct kunit *test)
> > +{
> > +	static const int expect[16] = {
> > +		1, 2, 4, 6, 8, 10, 12, 14, 16, 20, 24, 28, 32,
> > +		-ENXIO, -ENXIO, -ENXIO,
> 
> Can we make the mapping of bit to value more explicit?
> 		[0x0] = 1,
> 		[0x1] = 2, [0x2] = 4, [0x3] = 6, [0x4] = 8,
> 		[0x5] = 10, [0x6] = 12, [0x7] = 14, [0x8] = 16,
> 		[0x9] = 20, [0xA] = 24, [0xB] = 28, [0xC] = 32,
> 		-ENXIO, -ENXIO, -ENXIO,
> //hex is to match spec that just lists these one by one by hex value.

Thanks Jonathan!

Added to my v2 prep but w a different handling of those trailing ENXIO's 

static const int expect[16] = {
	[0x0] = 1,
	[0x1] = 2, [0x2] = 4, [0x3] = 6, [0x4] = 8,
	[0x5] = 10, [0x6] = 12, [0x7] = 14, [0x8] = 16,
	[0x9] = 20, [0xA] = 24, [0xB] = 28, [0xC] = 32,
	[0xD ... 0xF] = -ENXIO,
};

-- Alison