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

[Davidlohr Bueso]

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