[PATCH v3 6/6] cxl/mem: Replace redundant debug message with a comment

From: Dan Williams <dan.j.williams@intel.com>
To: linux-cxl@vger.kernel.org
Cc: Ben Widawsky <ben.widawsky@intel.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Davidlohr Bueso <dave@stgolabs.net>
Subject: [PATCH v3 6/6] cxl/mem: Replace redundant debug message with a comment
Date: Fri, 08 Apr 2022 12:30:29 -0700	[thread overview]
Message-ID: <164944616743.454665.7055846627973202403.stgit@dwillia2-desk3.amr.corp.intel.com> (raw)
In-Reply-To: <164730736948.3806189.17828261054974867700.stgit@dwillia2-desk3.amr.corp.intel.com>

cxl_mem_probe() already emits a log message when HDM operation can not
be established. Delete the similar one in cxl_hdm_decode_init().

What is less obvious is why global_ctrl being enabled makes positive
values of info->ranges irrelevant, and the Linux behavior with respect
to the spec recommendation to mirror CXL Range registers with HDM
Decoder Base + Size registers.

Cc: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Changes since v2:
- Clarify that Linux does not maintain the spec recommended match
  between HDM decoders and CXL DVSEC range registers. (Ben and Jonathan)

 drivers/cxl/mem.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 3baae1332760..43e73d259207 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -107,11 +107,17 @@ __mock bool cxl_hdm_decode_init(struct cxl_dev_state *cxlds)
 	global_ctrl = readl(crb + cmap->hdm_decoder.offset +
 			    CXL_HDM_DECODER_CTRL_OFFSET);
 	global_enable = global_ctrl & CXL_HDM_DECODER_ENABLE;
-	if (!global_enable && info->ranges) {
-		dev_dbg(cxlds->dev,
-			"DVSEC ranges already programmed and HDM decoders not enabled.\n");
+
+	/*
+	 * 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->ranges)
 		goto out;
-	}
 
 	retval = true;
 

