linux-kernel - [tip:x86/timers] x86/hpet: Add function to select a /dev/hpet channel

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Date:   Thu, 27 Jun 2019 16:48:17 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, eranian@...gle.com,
        Suravee.Suthikulpanit@....com, tglx@...utronix.de,
        ashok.raj@...el.com, mingo@...nel.org, ravi.v.shankar@...el.com,
        peterz@...radead.org, hpa@...or.com, andi.kleen@...el.com,
        ricardo.neri-calderon@...ux.intel.com
Subject: [tip:x86/timers] x86/hpet: Add function to select a /dev/hpet
 channel

Commit-ID:  af5a1dadf3fcf673906af1a1129b2b7528494ee5
Gitweb:     https://git.kernel.org/tip/af5a1dadf3fcf673906af1a1129b2b7528494ee5
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sun, 23 Jun 2019 15:24:01 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 28 Jun 2019 00:57:23 +0200

x86/hpet: Add function to select a /dev/hpet channel

If CONFIG_HPET=y is enabled the x86 specific HPET code should reserve at
least one channel for the /dev/hpet character device, so that not all
channels are absorbed for per CPU clockevent devices.

Create a function to assign HPET_MODE_DEVICE so the rework of the
clockevents allocation code can utilize the mode information instead of
reducing the number of evaluated channels by #ifdef hackery.

The function is not yet used, but provided as a separate patch for ease of
review. It will be used when the rework of the clockevent selection takes
place.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: Ashok Raj <ashok.raj@...el.com>
Cc: Andi Kleen <andi.kleen@...el.com>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Ravi Shankar <ravi.v.shankar@...el.com>
Link: https://lkml.kernel.org/r/20190623132436.002758910@linutronix.de

---
 arch/x86/kernel/hpet.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 3a8ec363d569..640ff75cc523 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -228,8 +228,25 @@ static void __init hpet_reserve_platform_timers(void)
 	hpet_alloc(&hd);
 
 }
+
+static void __init hpet_select_device_channel(void)
+{
+	int i;
+
+	for (i = 0; i < hpet_base.nr_channels; i++) {
+		struct hpet_channel *hc = hpet_base.channels + i;
+
+		/* Associate the first unused channel to /dev/hpet */
+		if (hc->mode == HPET_MODE_UNUSED) {
+			hc->mode = HPET_MODE_DEVICE;
+			return;
+		}
+	}
+}
+
 #else
 static inline void hpet_reserve_platform_timers(void) { }
+static inline void hpet_select_device_channel(void) {}
 #endif
 
 /* Common HPET functions */