[PATCH 2/5] cxl/hdm: Use 4-byte reads to retrieve HDM decoder base+limit

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

The CXL specification mandates that 4-byte registers must be accessed
with 4-byte access cycles. CXL 3.0 8.2.3 "Component Register Layout and
Definition" states that the behavior is undefined if (2) 32-bit
registers are accessed as an 8-byte quantity. It turns out that at least
one hardware implementation is sensitive to this in practice. The @size
variable results in zero with:

    size = readq(hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(which));

...and the correct size with:

    lo = readl(hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(which));
    hi = readl(hdm + CXL_HDM_DECODER0_SIZE_HIGH_OFFSET(which));
    size = (hi << 32) + lo;

Fixes: d17d0540a0db ("cxl/core/hdm: Add CXL standard decoder enumeration to the core")
Cc: <stable@vger.kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/cxl/core/hdm.c |   20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 35b338b716fe..6fdf7981ddc7 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -1,6 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2022 Intel Corporation. All rights reserved. */
-#include <linux/io-64-nonatomic-hi-lo.h>
 #include <linux/seq_file.h>
 #include <linux/device.h>
 #include <linux/delay.h>
@@ -785,8 +784,8 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 			    int *target_map, void __iomem *hdm, int which,
 			    u64 *dpa_base, struct cxl_endpoint_dvsec_info *info)
 {
+	u64 size, base, skip, dpa_size, lo, hi;
 	struct cxl_endpoint_decoder *cxled;
-	u64 size, base, skip, dpa_size;
 	bool committed;
 	u32 remainder;
 	int i, rc;
@@ -801,8 +800,12 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 							which, info);
 
 	ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(which));
-	base = ioread64_hi_lo(hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(which));
-	size = ioread64_hi_lo(hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(which));
+	lo = readl(hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(which));
+	hi = readl(hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(which));
+	base = (hi << 32) + lo;
+	lo = readl(hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(which));
+	hi = readl(hdm + CXL_HDM_DECODER0_SIZE_HIGH_OFFSET(which));
+	size = (hi << 32) + lo;
 	committed = !!(ctrl & CXL_HDM_DECODER0_CTRL_COMMITTED);
 	cxld->commit = cxl_decoder_commit;
 	cxld->reset = cxl_decoder_reset;
@@ -865,8 +868,9 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 		return rc;
 
 	if (!info) {
-		target_list.value =
-			ioread64_hi_lo(hdm + CXL_HDM_DECODER0_TL_LOW(which));
+		lo = readl(hdm + CXL_HDM_DECODER0_TL_LOW(which));
+		hi = readl(hdm + CXL_HDM_DECODER0_TL_HIGH(which));
+		target_list.value = (hi << 32) + lo;
 		for (i = 0; i < cxld->interleave_ways; i++)
 			target_map[i] = target_list.target_id[i];
 
@@ -883,7 +887,9 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 			port->id, cxld->id, size, cxld->interleave_ways);
 		return -ENXIO;
 	}
-	skip = ioread64_hi_lo(hdm + CXL_HDM_DECODER0_SKIP_LOW(which));
+	lo = readl(hdm + CXL_HDM_DECODER0_SKIP_LOW(which));
+	hi = readl(hdm + CXL_HDM_DECODER0_SKIP_HIGH(which));
+	skip = (hi << 32) + lo;
 	cxled = to_cxl_endpoint_decoder(&cxld->dev);
 	rc = devm_cxl_dpa_reserve(cxled, *dpa_base + skip, dpa_size, skip);
 	if (rc) {