[PATCH] cxl/hdm: Fix decoder count calculation

[PATCH] cxl/hdm: Fix decoder count calculation

[Ben Widawsky]

The decoder count in the HDM decoder capability structure is an encoded
field. As defined in the spec:

Decoder Count: Reports the number of memory address decoders implemented
by the component.
0 – 1 Decoder
1 – 2 Decoders
2 – 4 Decoders
3 – 6 Decoders
4 – 8 Decoders
5 – 10 DecodersAll other values are reserved

Nothing is actually fixed by this as nothing actually used this mapping
yet.

Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
 drivers/cxl/core.c | 3 ++-
 drivers/cxl/cxl.h  | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
index cda09a9cd98e..92db02fe7aa8 100644
--- a/drivers/cxl/core.c
+++ b/drivers/cxl/core.c
@@ -666,7 +666,8 @@ void cxl_probe_component_regs(struct device *dev, void __iomem *base,
 
 			hdr = readl(register_block);
 
-			decoder_cnt = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr);
+			decoder_cnt =
+				cxl_hdm_decoder_count(FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr));
 			length = 0x20 * decoder_cnt + 0x10;
 
 			map->hdm_decoder.valid = true;
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 1ffc5e07e24d..f0dff7d96286 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -35,6 +35,7 @@
 /* HDM decoders CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure */
 #define CXL_HDM_DECODER_CAP_OFFSET 0x0
 #define   CXL_HDM_DECODER_COUNT_MASK GENMASK(3, 0)
+#define	    cxl_hdm_decoder_count(bits) ((bits) == 0 ? 1 : (bits) * 2)
 #define   CXL_HDM_DECODER_TARGET_COUNT_MASK GENMASK(7, 4)
 #define CXL_HDM_DECODER0_BASE_LOW_OFFSET 0x10
 #define CXL_HDM_DECODER0_BASE_HIGH_OFFSET 0x14
-- 
2.32.0

Re: [PATCH] cxl/hdm: Fix decoder count calculation

[Dan Williams]

On Thu, Jun 10, 2021 at 2:53 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> The decoder count in the HDM decoder capability structure is an encoded
> field. As defined in the spec:
>
> Decoder Count: Reports the number of memory address decoders implemented
> by the component.
> 0 – 1 Decoder
> 1 – 2 Decoders
> 2 – 4 Decoders
> 3 – 6 Decoders
> 4 – 8 Decoders
> 5 – 10 DecodersAll other values are reserved
>
> Nothing is actually fixed by this as nothing actually used this mapping
> yet.
>
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> ---
>  drivers/cxl/core.c | 3 ++-
>  drivers/cxl/cxl.h  | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> index cda09a9cd98e..92db02fe7aa8 100644
> --- a/drivers/cxl/core.c
> +++ b/drivers/cxl/core.c
> @@ -666,7 +666,8 @@ void cxl_probe_component_regs(struct device *dev, void __iomem *base,
>
>                         hdr = readl(register_block);
>
> -                       decoder_cnt = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr);
> +                       decoder_cnt =
> +                               cxl_hdm_decoder_count(FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr));

How about make it a static inline helper that takes @hdr and move the
FIELD_GET inside there to save some indentation?

I still think it warrants a Fixes: tag, the commit ids in cxl.git/next
are stable.

Re: [PATCH] cxl/hdm: Fix decoder count calculation

[Jonathan Cameron]

On Thu, 10 Jun 2021 14:53:32 -0700
Ben Widawsky <ben.widawsky@intel.com> wrote:

> The decoder count in the HDM decoder capability structure is an encoded
> field. As defined in the spec:
> 
> Decoder Count: Reports the number of memory address decoders implemented
> by the component.
> 0 – 1 Decoder
> 1 – 2 Decoders
> 2 – 4 Decoders
> 3 – 6 Decoders
> 4 – 8 Decoders
> 5 – 10 DecodersAll other values are reserved
> 
> Nothing is actually fixed by this as nothing actually used this mapping
> yet.
> 
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
lgtm.

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  drivers/cxl/core.c | 3 ++-
>  drivers/cxl/cxl.h  | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> index cda09a9cd98e..92db02fe7aa8 100644
> --- a/drivers/cxl/core.c
> +++ b/drivers/cxl/core.c
> @@ -666,7 +666,8 @@ void cxl_probe_component_regs(struct device *dev, void __iomem *base,
>  
>  			hdr = readl(register_block);
>  
> -			decoder_cnt = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr);
> +			decoder_cnt =
> +				cxl_hdm_decoder_count(FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr));
>  			length = 0x20 * decoder_cnt + 0x10;
>  
>  			map->hdm_decoder.valid = true;
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 1ffc5e07e24d..f0dff7d96286 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -35,6 +35,7 @@
>  /* HDM decoders CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure */
>  #define CXL_HDM_DECODER_CAP_OFFSET 0x0
>  #define   CXL_HDM_DECODER_COUNT_MASK GENMASK(3, 0)
> +#define	    cxl_hdm_decoder_count(bits) ((bits) == 0 ? 1 : (bits) * 2)
>  #define   CXL_HDM_DECODER_TARGET_COUNT_MASK GENMASK(7, 4)
>  #define CXL_HDM_DECODER0_BASE_LOW_OFFSET 0x10
>  #define CXL_HDM_DECODER0_BASE_HIGH_OFFSET 0x14

[PATCH v2] cxl/hdm: Fix decoder count calculation

[Ben Widawsky]

The decoder count in the HDM decoder capability structure is an encoded
field. As defined in the spec:

Decoder Count: Reports the number of memory address decoders implemented
by the component.
0 – 1 Decoder
1 – 2 Decoders
2 – 4 Decoders
3 – 6 Decoders
4 – 8 Decoders
5 – 10 Decoders
All other values are reserved

Nothing is actually fixed by this as nothing actually used this mapping
yet.

Cc: Ira Weiny <ira.weiny@intel.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
v2:
- Minor whitespace cleanup in commit message.
- Move value decoder to inline function. (Dan)
- Rework value decoding logic to be more concise.
---
 drivers/cxl/core.c | 2 +-
 drivers/cxl/cxl.h  | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
index 6db660249cea..49744ad885de 100644
--- a/drivers/cxl/core.c
+++ b/drivers/cxl/core.c
@@ -603,7 +603,7 @@ void cxl_probe_component_regs(struct device *dev, void __iomem *base,
 
 			hdr = readl(register_block);
 
-			decoder_cnt = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, hdr);
+			decoder_cnt = cxl_hdm_decoder_count(hdr);
 			length = 0x20 * decoder_cnt + 0x10;
 
 			map->hdm_decoder.valid = true;
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 3f9a6f7b05db..f1e52487c644 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -42,6 +42,13 @@
 #define CXL_HDM_DECODER0_SIZE_HIGH_OFFSET 0x1c
 #define CXL_HDM_DECODER0_CTRL_OFFSET 0x20
 
+static inline int cxl_hdm_decoder_count(u32 cap_hdr)
+{
+	int val = FIELD_GET(CXL_HDM_DECODER_COUNT_MASK, cap_hdr);
+
+	return val ? val * 2 : 1;
+}
+
 /* CXL 2.0 8.2.8.1 Device Capabilities Array Register */
 #define CXLDEV_CAP_ARRAY_OFFSET 0x0
 #define   CXLDEV_CAP_ARRAY_CAP_ID 0
-- 
2.32.0

Re: [PATCH v2] cxl/hdm: Fix decoder count calculation

[Dan Williams]

On Fri, Jun 11, 2021 at 12:01 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> The decoder count in the HDM decoder capability structure is an encoded
> field. As defined in the spec:
>
> Decoder Count: Reports the number of memory address decoders implemented
> by the component.
> 0 – 1 Decoder
> 1 – 2 Decoders
> 2 – 4 Decoders
> 3 – 6 Decoders
> 4 – 8 Decoders
> 5 – 10 Decoders
> All other values are reserved
>
> Nothing is actually fixed by this as nothing actually used this mapping
> yet.

I'll still add the Fixes tag because the original commit is broken
even if the impact of fixing this bug is moot in the near term.