linux-kernel - [PATCH v2 2/3] x86/platform/uv: Update TSC sync state for UV5

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Date:   Tue, 15 Mar 2022 10:42:48 -0500
From:   Mike Travis <mike.travis@....com>
To:     Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steve Wahl <steve.wahl@....com>, x86@...nel.org
Cc:     Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: [PATCH v2 2/3] x86/platform/uv: Update TSC sync state for UV5

Update TSC to not check TSC sync state for uv5+ as it is not available.
It is assumed that TSC will always be in sync for multiple chassis and
will pass the tests for the kernel to accept it as the clocksource.
To disable this check use the kernel start options tsc=reliable
clocksource=tsc.

Signed-off-by: Mike Travis <mike.travis@....com>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@....com>
Reviewed-by: Steve Wahl <steve.wahl@....com>
---
v2: Update patch description to be more explanatory.
---
 arch/x86/kernel/apic/x2apic_uv_x.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index f5a48e66e4f5..387d6533549a 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -199,10 +199,16 @@ static void __init uv_tsc_check_sync(void)
 	int mmr_shift;
 	char *state;
 
-	/* Different returns from different UV BIOS versions */
+	/* UV5+, sync state from bios not available, assumed valid */
+	if (!is_uv(UV2|UV3|UV4)) {
+		pr_debug("UV: TSC sync state for UV5+ assumed valid\n");
+		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;
+	mmr_shift = is_uv2_hub() ? UVH_TSC_SYNC_SHIFT_UV2K : UVH_TSC_SYNC_SHIFT;
 	sync_state = (mmr >> mmr_shift) & UVH_TSC_SYNC_MASK;
 
 	/* Check if TSC is valid for all sockets */
-- 
2.26.2