@@ -5,6 +5,7 @@
#include <linux/mutex.h>
#include <linux/pci.h>
#include <linux/slab.h>
+#include <linux/spinlock.h>
#include <linux/xarray.h>
#include "ice_adapter.h"
@@ -28,6 +29,7 @@ static struct ice_adapter *ice_adapter_new(void)
if (!adapter)
return NULL;
+ spin_lock_init(&adapter->ptp_gltsyn_time_lock);
refcount_set(&adapter->refcount, 1);
return adapter;
@@ -4,15 +4,21 @@
#ifndef _ICE_ADAPTER_H_
#define _ICE_ADAPTER_H_
+#include <linux/spinlock_types.h>
#include <linux/refcount_types.h>
struct pci_dev;
/**
* struct ice_adapter - PCI adapter resources shared across PFs
+ * @ptp_gltsyn_time_lock: Spinlock protecting access to the GLTSYN_TIME
+ * register of the PTP clock.
* @refcount: Reference count. struct ice_pf objects hold the references.
*/
struct ice_adapter {
+ /* For access to the GLTSYN_TIME register */
+ spinlock_t ptp_gltsyn_time_lock;
+
refcount_t refcount;
};
@@ -374,6 +374,7 @@ ice_ptp_read_src_clk_reg(struct ice_pf *pf, struct ptp_system_timestamp *sts)
u8 tmr_idx;
tmr_idx = ice_get_ptp_src_clock_index(hw);
+ guard(spinlock)(&pf->adapter->ptp_gltsyn_time_lock);
/* Read the system timestamp pre PHC read */
ptp_read_system_prets(sts);
@@ -1925,15 +1926,8 @@ ice_ptp_gettimex64(struct ptp_clock_info *info, struct timespec64 *ts,
struct ptp_system_timestamp *sts)
{
struct ice_pf *pf = ptp_info_to_pf(info);
- struct ice_hw *hw = &pf->hw;
-
- if (!ice_ptp_lock(hw)) {
- dev_err(ice_pf_to_dev(pf), "PTP failed to get time\n");
- return -EBUSY;
- }
ice_ptp_read_time(pf, ts, sts);
- ice_ptp_unlock(hw);
return 0;
}
@@ -274,6 +274,9 @@ void ice_ptp_src_cmd(struct ice_hw *hw, enum ice_ptp_tmr_cmd cmd)
*/
static void ice_ptp_exec_tmr_cmd(struct ice_hw *hw)
{
+ struct ice_pf *pf = container_of(hw, struct ice_pf, hw);
+
+ guard(spinlock)(&pf->adapter->ptp_gltsyn_time_lock);
wr32(hw, GLTSYN_CMD_SYNC, SYNC_EXEC_CMD);
ice_flush(hw);
}
The PTP hardware semaphore (PFTSYN_SEM) is used to synchronize operations that program the PTP timers. The operations involve issuing commands to the sideband queue. The E810 does not have a hardware sideband queue, so the admin queue is used. The admin queue is slow. I have observed delays in hundreds of milliseconds waiting for ice_sq_done. When phc2sys reads the time from the ice PTP clock and PFTSYN_SEM is held by a task performing one of the slow operations, ice_ptp_lock can easily time out. phc2sys gets -EBUSY and the kernel prints: ice 0000:XX:YY.0: PTP failed to get time These messages appear once every few seconds, causing log spam. The E810 datasheet recommends an algorithm for reading the upper 64 bits of the GLTSYN_TIME register. It matches what's implemented in ice_ptp_read_src_clk_reg. It is robust against wrap-around, but not necessarily against the concurrent setting of the register (with GLTSYN_CMD_{INIT,ADJ}_TIME commands). Perhaps that's why ice_ptp_gettimex64 also takes PFTSYN_SEM. The race with time setters can be prevented without relying on the PTP hardware semaphore. Using the "ice_adapter" from the previous patch, we can have a common spinlock for the PFs that share the clock hardware. It will protect the reading and writing to the GLTSYN_TIME register. The writing is performed indirectly, by the hardware, as a result of the driver writing GLTSYN_CMD_SYNC in ice_ptp_exec_tmr_cmd. I wasn't sure if the ice_flush there is enough to make sure GLTSYN_TIME has been updated, but it works well in my testing. My test code can be seen here: https://gitlab.com/mschmidt2/linux/-/commits/ice-ptp-host-side-lock-9 It consists of: - kernel threads reading the time in a busy loop and looking at the deltas between consecutive values, reporting new maxima. - a shell script that sets the time repeatedly; - a bpftrace probe to produce a histogram of the measured deltas. Without the spinlock ptp_gltsyn_time_lock, it is easy to see tearing. Deltas in the [2G, 4G) range appear in the histograms. With the spinlock added, there is no tearing and the biggest delta I saw was in the range [1M, 2M), that is under 2 ms. Signed-off-by: Michal Schmidt <mschmidt@redhat.com> --- drivers/net/ethernet/intel/ice/ice_adapter.c | 2 ++ drivers/net/ethernet/intel/ice/ice_adapter.h | 6 ++++++ drivers/net/ethernet/intel/ice/ice_ptp.c | 8 +------- drivers/net/ethernet/intel/ice/ice_ptp_hw.c | 3 +++ 4 files changed, 12 insertions(+), 7 deletions(-)