[PATCH 09/14] cxl/mem: Fix CXL DVSEC Range Sizing

[Dan Williams <dan.j.williams@intel.com>]

Per CXL 2.0 Section 8.1.3.8.4 "DVSEC CXL Range 1 Base Low" there is no
way to specify decode sizes smaller than 256M. Fix cxl_dvsec_ranges()
and cxl_hdm_decode_init() to account for that default decode range.
Note, that this means that any BIOS implementation that sets mem_enable,
but not HDM Decoder Capability enable will cause the driver to fail to
attach. A later change validates the DVSEC ranges against platform CXL
decode (CXL CFMWS) to make a decision about overriding the default DVSEC
Range configuration.

Fixes: 560f78559006 ("cxl/pci: Retrieve CXL DVSEC memory info")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/cxl/core/pci.c |   10 +++++++---
 drivers/cxl/mem.c      |   10 +---------
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index f3e59f8b6621..f1c0677a4f52 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -236,7 +236,12 @@ int cxl_dvsec_ranges(struct cxl_dev_state *cxlds,
 		if (rc)
 			return rc;
 
-		size = (u64)temp << 32;
+		/*
+		 * Per CXL 2.0 Section 8.1.3.8.4 "DVSEC CXL Range 1 Base
+		 * Low", the minimum decode size is 256MB
+		 */
+		size = SZ_256M;
+		size |= (u64)temp << 32;
 
 		rc = pci_read_config_dword(
 			pdev, d + CXL_DVSEC_RANGE_SIZE_LOW(i), &temp);
@@ -264,8 +269,7 @@ int cxl_dvsec_ranges(struct cxl_dev_state *cxlds,
 			.end = base + size - 1
 		};
 
-		if (size)
-			ranges++;
+		ranges++;
 	}
 
 	info->ranges = ranges;
diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 902d1f6e189e..af4a88d3c5fa 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -84,15 +84,7 @@ __mock bool cxl_hdm_decode_init(struct cxl_dev_state *cxlds,
 			    CXL_HDM_DECODER_CTRL_OFFSET);
 	global_enable = global_ctrl & CXL_HDM_DECODER_ENABLE;
 
-	/*
-	 * Per CXL 2.0 Section 8.1.3.8.3 and 8.1.3.8.4 DVSEC CXL Range 1 Base
-	 * [High,Low] when HDM operation is enabled the range register values
-	 * are ignored by the device, but the spec also recommends matching the
-	 * DVSEC Range 1,2 to HDM Decoder Range 0,1. So, non-zero info->ranges
-	 * are expected even though Linux does not require or maintain that
-	 * match.
-	 */
-	if (!global_enable && info->mem_enabled && info->ranges)
+	if (!global_enable && info->mem_enabled)
 		goto out;
 
 	retval = true;