linux-kernel - [PATCH v4 2/3] x86/platform/uv: Update TSC sync state for UV5

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Message-Id: <20220406195149.228164-3-steve.wahl@hpe.com>
Date:   Wed,  6 Apr 2022 14:51:48 -0500
From:   Steve Wahl <steve.wahl@....com>
To:     Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Mike Travis <mike.travis@....com>, Steve Wahl <steve.wahl@....com>,
        Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: [PATCH v4 2/3] x86/platform/uv: Update TSC sync state for UV5

From: Mike Travis <mike.travis@....com>

The UV5 platform synchronizes the TSCs among all chassis, and will not
proceed to OS boot without achieving synchronization.  Previous UV
platforms provided a register indicating successful synchronization.
This is no longer available on UV5.  On this platform TSC_ADJUST
should not be reset by the kernel.

Signed-off-by: Mike Travis <mike.travis@....com>
Signed-off-by: Steve Wahl <steve.wahl@....com>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@....com>
---
v2: Update patch description to be more explanatory.

v4: Update patch description to provide better context
    Removed a pr_debug() and an unrelated whitespace change
---
 arch/x86/kernel/apic/x2apic_uv_x.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index f5a48e66e4f5..a6e9c2794ef5 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -199,7 +199,13 @@ static void __init uv_tsc_check_sync(void)
 	int mmr_shift;
 	char *state;
 
-	/* Different returns from different UV BIOS versions */
+	/* UV5 guarantees synced TSCs; do not zero TSC_ADJUST */
+	if (!is_uv(UV2|UV3|UV4)) {
+		mark_tsc_async_resets("UV5+");
+		return;
+	}
+
+	/* UV2,3,4, UV BIOS TSC sync state available */
 	mmr = uv_early_read_mmr(UVH_TSC_SYNC_MMR);
 	mmr_shift =
 		is_uv2_hub() ? UVH_TSC_SYNC_SHIFT_UV2K : UVH_TSC_SYNC_SHIFT;
-- 
2.26.2