Re: [PATCH] cxl: Replace HDM decoder granularity magic numbers

From: Davidlohr Bueso
Date: Mon Aug 22 2022 - 13:35:16 EST


On Mon, 22 Aug 2022, Adam Manzanares wrote:

When reviewing the CFMWS parsing code that deals with the HDM decoders,
I noticed a couple of magic numbers. This commit replaces these magic numbers
with constants defined by the CXL 2.0 specification.

Please use 3.0 spec :)

Actually the whole drivers/cxl/* could use updating the comments for 3.0.

Signed-off-by: Adam Manzanares <a.manzanares@xxxxxxxxxxx>
---
drivers/cxl/cxl.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index f680450f0b16..ba3a66b5b9cd 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -61,6 +61,10 @@
#define CXL_HDM_DECODER0_SKIP_LOW(i) CXL_HDM_DECODER0_TL_LOW(i)
#define CXL_HDM_DECODER0_SKIP_HIGH(i) CXL_HDM_DECODER0_TL_HIGH(i)

+/* HDM decoder control register constants CXL 2.0 8.2.5.12.7 */

This now becomes 8.2.4.19.7.

+#define CXL_DECODER_MIN_GRANULARITY 256
+#define CXL_DECODER_MAX_GRANULARITY_ORDER 6

Considering there is a single user, I don't think we need to add
the CXL_DECODER_MAX_GRANULARITY_ORDER. And if a new one is added
it would be better to keep symmetry (bytes) and just do
CXL_DECODER_MAX_GRANULARITY, but that's probably the reason why
it doesn't exist in the first place.

+
static inline int cxl_hdm_decoder_count(u32 cap_hdr)
{
int val = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, cap_hdr);
@@ -71,9 +75,9 @@ static inline int cxl_hdm_decoder_count(u32 cap_hdr)
/* Encode defined in CXL 2.0 8.2.5.12.7 HDM Decoder Control Register */
static inline int cxl_to_granularity(u16 ig, unsigned int *val)
{
- if (ig > 6)
+ if (ig > CXL_DECODER_MAX_GRANULARITY_ORDER)
return -EINVAL;
- *val = 256 << ig;
+ *val = CXL_DECODER_MIN_GRANULARITY << ig;
return 0;
}

@@ -96,7 +100,7 @@ static inline int cxl_to_ways(u8 eniw, unsigned int *val)

static inline int granularity_to_cxl(int g, u16 *ig)
{
- if (g > SZ_16K || g < 256 || !is_power_of_2(g))
+ if (g > SZ_16K || g < CXL_DECODER_MIN_GRANULARITY || !is_power_of_2(g))

Looks good.

Thanks,
Davidlohr