linux-kernel - Re: [PATCH v2] cxl: Replace HDM decoder granularity magic numbers

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Date:   Wed, 28 Sep 2022 08:45:02 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Adam Manzanares <a.manzanares@...sung.com>,
        "alison.schofield@...el.com" <alison.schofield@...el.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "bwidawsk@...nel.org" <bwidawsk@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>
Cc:     "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cxl: Replace HDM decoder granularity magic numbers


On 8/29/2022 3:03 PM, 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 3.0 specification.
>
> v2:
>   - Change references to CXL 3.0 specification (David)
>   - CXL_DECODER_MAX_GRANULARITY_ORDER -> CXL_DECODER_MAX_ENCODED_IG (Dan)
>
> Signed-off-by: Adam Manzanares <a.manzanares@...sung.com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>


> ---
>   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..3ab81ad9d2e5 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 3.0 8.2.5.19.7 */
> +#define CXL_DECODER_MIN_GRANULARITY 256
> +#define CXL_DECODER_MAX_ENCODED_IG 6
> +
>   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_ENCODED_IG)
>   		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))
>   		return -EINVAL;
>   	*ig = ilog2(g) - 8;
>   	return 0;
> @@ -248,7 +252,6 @@ enum cxl_decoder_type {
>    */
>   #define CXL_DECODER_MAX_INTERLEAVE 16
>   
> -#define CXL_DECODER_MIN_GRANULARITY 256
>   
>   /**
>    * struct cxl_decoder - Common CXL HDM Decoder Attributes