RE: [net-next, v3, 01/10] ptp: add ptp virtual clock driver framework

Hi Richard,

-----Original Message-----
From: Richard Cochran <richardcochran@gmail.com>
Sent: 2021年6月18日 1:33
To: Y.b. Lu <yangbo.lu@nxp.com>
Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org;
linux-kselftest@vger.kernel.org; mptcp@lists.linux.dev; David S . Miller
[off-list ref]; Jakub Kicinski [off-list ref]; Mat Martineau
[off-list ref]; Matthieu Baerts
[off-list ref]; Shuah Khan [off-list ref]; Michal
Kubecek [off-list ref]; Florian Fainelli [off-list ref];
Andrew Lunn [off-list ref]; Rui Sousa [off-list ref]; Sebastien
Laveze [off-list ref]
Subject: Re: [net-next, v3, 01/10] ptp: add ptp virtual clock driver framework

On Tue, Jun 15, 2021 at 05:45:08PM +0800, Yangbo Lu wrote:

quoted

diff --git a/drivers/ptp/Makefile b/drivers/ptp/Makefile index

8673d1743faa..3c6a905760e2 100644

--- a/drivers/ptp/Makefile
+++ b/drivers/ptp/Makefile

@@ -3,7 +3,7 @@
 # Makefile for PTP 1588 clock support.
 #

-ptp-y					:= ptp_clock.o ptp_chardev.o ptp_sysfs.o
+ptp-y					:= ptp_clock.o ptp_vclock.o ptp_chardev.o

ptp_sysfs.o

Nit: Please place ptp_vclock.o at the end of the list.

Ok.

quoted

 ptp_kvm-$(CONFIG_X86)			:= ptp_kvm_x86.o ptp_kvm_common.o
 ptp_kvm-$(CONFIG_HAVE_ARM_SMCCC)	:= ptp_kvm_arm.o

ptp_kvm_common.o

quoted

 obj-$(CONFIG_PTP_1588_CLOCK)		+= ptp.o

quoted

diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h
index 6b97155148f1..3f388d63904c 100644
--- a/drivers/ptp/ptp_private.h
+++ b/drivers/ptp/ptp_private.h

@@ -48,6 +48,20 @@ struct ptp_clock {
 	struct kthread_delayed_work aux_work;  };

+#define info_to_vclock(d) container_of((d), struct ptp_vclock, info)
+#define cc_to_vclock(d) container_of((d), struct ptp_vclock, cc)
+#define dw_to_vclock(d) container_of((d), struct ptp_vclock,
+refresh_work)
+
+struct ptp_vclock {
+	struct ptp_clock *pclock;
+	struct ptp_clock_info info;
+	struct ptp_clock *clock;
+	struct cyclecounter cc;
+	struct timecounter tc;
+	spinlock_t lock;	/* protects tc/cc */
+	struct delayed_work refresh_work;

Can we please have a kthread worker here instead of work?

Experience shows that plain work can be delayed for a long, long time on busy
systems.

I think do_aux_work callback could be utilized for ptp virtual clock, right?

quoted

+};
+
 /*
  * The function queue_cnt() is safe for readers to call without
  * holding q->lock. Readers use this function to verify that the
queue @@ -89,4 +103,6 @@ extern const struct attribute_group
*ptp_groups[];  int ptp_populate_pin_groups(struct ptp_clock *ptp);
void ptp_cleanup_pin_groups(struct ptp_clock *ptp);

+struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock);
+void ptp_vclock_unregister(struct ptp_vclock *vclock);
 #endif

quoted

diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c new

file mode 100644 index 000000000000..b8f500677314

--- /dev/null
+++ b/drivers/ptp/ptp_vclock.c

@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PTP virtual clock driver
+ *
+ * Copyright 2021 NXP
+ */
+#include <linux/slab.h>
+#include "ptp_private.h"
+
+#define PTP_VCLOCK_CC_MULT		(1 << 31)
+#define PTP_VCLOCK_CC_SHIFT		31

These two are okay, but ...

quoted

+#define PTP_VCLOCK_CC_MULT_NUM		(1 << 9)
+#define PTP_VCLOCK_CC_MULT_DEM		15625ULL

the similarity of naming is confusing for these two.  They are only used in
the .adjfine method.  How about this?

  PTP_VCLOCK_FADJ_NUMERATOR, or even PTP_VCLOCK_FADJ_SHIFT (see
below)
  PTP_VCLOCK_FADJ_DENOMINATOR

quoted

+#define PTP_VCLOCK_CC_REFRESH_INTERVAL	(HZ * 2)

Consider dropping CC from the name.
PTP_VCLOCK_REFRESH_INTERVAL sounds good to me.

Thanks. Will rename the MACROs per your suggestion.

quoted

+static int ptp_vclock_adjfine(struct ptp_clock_info *ptp, long
+scaled_ppm) {
+	struct ptp_vclock *vclock = info_to_vclock(ptp);
+	unsigned long flags;
+	s64 adj;
+
+	adj = (s64)scaled_ppm * PTP_VCLOCK_CC_MULT_NUM;

Rather than

    scaled_ppm * (1 << 9)

I suggest

    scaled_ppm << 9

instead.  I suppose a good compiler would replace the multiplication with a
bit shift, but it never hurts to spell it out.

Ok.

quoted

+	adj = div_s64(adj, PTP_VCLOCK_CC_MULT_DEM);
+
+	spin_lock_irqsave(&vclock->lock, flags);
+	timecounter_read(&vclock->tc);
+	vclock->cc.mult = PTP_VCLOCK_CC_MULT + adj;
+	spin_unlock_irqrestore(&vclock->lock, flags);
+
+	return 0;
+}

Thanks,
Richard