linux-kernel - [PATCH 1/2] Revert "iommu/amd: Fix performance counter initialization"

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Date:   Fri,  9 Apr 2021 03:58:47 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org, will@...nel.org, jsnitsel@...hat.com,
        pmenzel@...gen.mpg.de, Jon.Grimm@....com,
        Tj <ml.linux@...oe.vision>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Alexander Monakov <amonakov@...ras.ru>,
        David Coe <david.coe@...e.co.uk>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH 1/2] Revert "iommu/amd: Fix performance counter initialization"

From: Paul Menzel <pmenzel@...gen.mpg.de>

This reverts commit 6778ff5b21bd8e78c8bd547fd66437cf2657fd9b.

The original commit tries to address an issue, where PMC power-gating
causing the IOMMU PMC pre-init test to fail on certain desktop/mobile
platforms where the power-gating is normally enabled.

There have been several reports that the workaround still does not
guarantee to work, and can add up to 100 ms (on the worst case)
to the boot process on certain platforms such as the MSI B350M MORTAR
with AMD Ryzen 3 2200G.

Therefore, revert this commit as a prelude to removing the pre-init
test.

Link: https://lore.kernel.org/linux-iommu/alpine.LNX.3.20.13.2006030935570.3181@monopod.intra.ispras.ru/
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201753
Cc: Tj (Elloe Linux) <ml.linux@...oe.vision>
Cc: Shuah Khan <skhan@...uxfoundation.org>
Cc: Alexander Monakov <amonakov@...ras.ru>
Cc: David Coe <david.coe@...e.co.uk>
Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
Note: I have revised the commit message to add more detail
      and remove uncessary information.

 drivers/iommu/amd/init.c | 45 ++++++++++------------------------------
 1 file changed, 11 insertions(+), 34 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 321f5906e6ed..648cdfd03074 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -12,7 +12,6 @@
 #include <linux/acpi.h>
 #include <linux/list.h>
 #include <linux/bitmap.h>
-#include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/syscore_ops.h>
 #include <linux/interrupt.h>
@@ -257,8 +256,6 @@ static enum iommu_init_state init_state = IOMMU_START_STATE;
 static int amd_iommu_enable_interrupts(void);
 static int __init iommu_go_to_state(enum iommu_init_state state);
 static void init_device_table_dma(void);
-static int iommu_pc_get_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr,
-				u8 fxn, u64 *value, bool is_write);
 
 static bool amd_iommu_pre_enabled = true;
 
@@ -1717,11 +1714,13 @@ static int __init init_iommu_all(struct acpi_table_header *table)
 	return 0;
 }
 
-static void __init init_iommu_perf_ctr(struct amd_iommu *iommu)
+static int iommu_pc_get_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr,
+				u8 fxn, u64 *value, bool is_write);
+
+static void init_iommu_perf_ctr(struct amd_iommu *iommu)
 {
-	int retry;
 	struct pci_dev *pdev = iommu->dev;
-	u64 val = 0xabcd, val2 = 0, save_reg, save_src;
+	u64 val = 0xabcd, val2 = 0, save_reg = 0;
 
 	if (!iommu_feature(iommu, FEATURE_PC))
 		return;
@@ -1729,39 +1728,17 @@ static void __init init_iommu_perf_ctr(struct amd_iommu *iommu)
 	amd_iommu_pc_present = true;
 
 	/* save the value to restore, if writable */
-	if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false) ||
-	    iommu_pc_get_set_reg(iommu, 0, 0, 8, &save_src, false))
-		goto pc_false;
-
-	/*
-	 * Disable power gating by programing the performance counter
-	 * source to 20 (i.e. counts the reads and writes from/to IOMMU
-	 * Reserved Register [MMIO Offset 1FF8h] that are ignored.),
-	 * which never get incremented during this init phase.
-	 * (Note: The event is also deprecated.)
-	 */
-	val = 20;
-	if (iommu_pc_get_set_reg(iommu, 0, 0, 8, &val, true))
+	if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, false))
 		goto pc_false;
 
 	/* Check if the performance counters can be written to */
-	val = 0xabcd;
-	for (retry = 5; retry; retry--) {
-		if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true) ||
-		    iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false) ||
-		    val2)
-			break;
-
-		/* Wait about 20 msec for power gating to disable and retry. */
-		msleep(20);
-	}
-
-	/* restore */
-	if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, true) ||
-	    iommu_pc_get_set_reg(iommu, 0, 0, 8, &save_src, true))
+	if ((iommu_pc_get_set_reg(iommu, 0, 0, 0, &val, true)) ||
+	    (iommu_pc_get_set_reg(iommu, 0, 0, 0, &val2, false)) ||
+	    (val != val2))
 		goto pc_false;
 
-	if (val != val2)
+	/* restore */
+	if (iommu_pc_get_set_reg(iommu, 0, 0, 0, &save_reg, true))
 		goto pc_false;
 
 	pci_info(pdev, "IOMMU performance counters supported\n");
-- 
2.17.1