[PATCH net-next] net: stmmac: ptp: switch to gettimex64() interface
Maxime Chevallier
maxime.chevallier at bootlin.com
Thu Oct 8 02:19:17 PDT 2026
Hi,
On 10/8/26 09:44, Nicolai Buchwitz wrote:
> Hi James
>
> On 6.10.2026 12:36, James Clark wrote:
>> The stmmac PTP support currently implements the gettime64 callback to
>> retrieve the hardware clock time. Update the implementation to provide
>> the gettimex64 callback instead, adding support for the
>> PTP_SYS_OFFSET_EXTENDED ioctl.
>>
>> The system clock readings are taken around the read of the nanoseconds
>> register in get_systime(), so get_systime() gains a ptp_system_timestamp
>> argument. rmb() is used to ensure proper ordering on weakly ordered
>> architectures.
>>
>> Assisted-by: LLM
>> Signed-off-by: James Clark <jjc at jclark.com>
>> ---
>> Tested on a Radxa ZERO 3E (RK3566, DWMAC 4/5) running net-next.
>> Width of the interval between the two system clock readings
>> bracketing each PHC read (2000 calls of 25 samples each):
>>
>> min median
>> Before patch (PTP_SYS_OFFSET): 875 ns 1167 ns
>> After patch (PTP_SYS_OFFSET_EXTENDED): 291 ns 584 ns
>>
>> On this board the 24 MHz arch timer counter advances in steps of 7
>> (~292 ns), so all intervals are multiples of that.
>
>> [...]
>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
>
>> [...]
>
>> @@ -191,8 +192,14 @@ static void get_systime(void __iomem *ioaddr, u64 *systime)
>> sec1 = readl_relaxed(ioaddr + PTP_STSR);
>> do {
>> sec0 = sec1;
>> + ptp_read_system_prets(sts);
>> + if (sts)
>> + rmb();
>> /* Get the TSSS value */
>> ns = readl_relaxed(ioaddr + PTP_STNSR);
>> + if (sts)
>> + rmb();
>> + ptp_read_system_postts(sts);
>
> Additional thought while testing on my stm32mp2:
>
> Would a plain readl() for PTP_STNSR be enough? readl() completes before
> a following delay loop, which is the counter read postts does. That would
> drop both barriers, like igb/ice/bnxt. Fine either way though, macb has
> the same rmb() pattern.
>
> Maxime (Chevallier), what do you think?
I agree yes, I was also wondering about just going to non-relaxed accessor
and drop the barriers.
Maxime
>
>> [...]
>
> Thanks,
> Nicolai
text:
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Subject: Re: [PATCH net-next] net: stmmac: ptp: switch to gettimex64()
interface
To: Nicolai Buchwitz <nb at tipi-net.de>, James Clark <jjc at jclark.com>
Cc: netdev at vger.kernel.org, Andrew Lunn <andrew+netdev at lunn.ch>,
"David S . Miller" <davem at davemloft.net>, Eric Dumazet
<edumazet at kernel.org>, Jakub Kicinski <kuba at kernel.org>,
Paolo Abeni <pabeni at redhat.com>, Richard Cochran <richardcochran at gmail.com>,
Miroslav Lichvar <mlichvar at redhat.com>,
Maxime Coquelin <mcoquelin.stm32 at gmail.com>,
Alexandre Torgue <alexandre.torgue at foss.st.com>,
linux-stm32 at st-md-mailman.stormreply.com,
linux-arm-kernel at lists.infradead.org, linux-kernel at vger.kernel.org
References: <20261006103610.98277-1-jjc at jclark.com>
<573ab838519f1fcfc19b5c03c23aa72f at tipi-net.de>
Content-Language: en-US
From: Maxime Chevallier <maxime.chevallier at bootlin.com>
In-Reply-To: <573ab838519f1fcfc19b5c03c23aa72f at tipi-net.de>
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X-Rspamd-Queue-Id: 95EDC1033384F
Hi,
On 10/8/26 09:44, Nicolai Buchwitz wrote:
> Hi James
>
> On 6.10.2026 12:36, James Clark wrote:
>> The stmmac PTP support currently implements the gettime64 callback to
>> retrieve the hardware clock time. Update the implementation to provide
>> the gettimex64 callback instead, adding support for the
>> PTP_SYS_OFFSET_EXTENDED ioctl.
>>
>> The system clock readings are taken around the read of the nanoseconds
>> register in get_systime(), so get_systime() gains a ptp_system_timestamp
>> argument. rmb() is used to ensure proper ordering on weakly ordered
>> architectures.
>>
>> Assisted-by: LLM
>> Signed-off-by: James Clark <jjc at jclark.com>
>> ---
>> Tested on a Radxa ZERO 3E (RK3566, DWMAC 4/5) running net-next.
>> Width of the interval between the two system clock readings
>> bracketing each PHC read (2000 calls of 25 samples each):
>>
>> min median
>> Before patch (PTP_SYS_OFFSET): 875 ns 1167 ns
>> After patch (PTP_SYS_OFFSET_EXTENDED): 291 ns 584 ns
>>
>> On this board the 24 MHz arch timer counter advances in steps of 7
>> (~292 ns), so all intervals are multiples of that.
>
>> [...]
>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
>
>> [...]
>
>> @@ -191,8 +192,14 @@ static void get_systime(void __iomem *ioaddr, u64 *systime)
>> sec1 = readl_relaxed(ioaddr + PTP_STSR);
>> do {
>> sec0 = sec1;
>> + ptp_read_system_prets(sts);
>> + if (sts)
>> + rmb();
>> /* Get the TSSS value */
>> ns = readl_relaxed(ioaddr + PTP_STNSR);
>> + if (sts)
>> + rmb();
>> + ptp_read_system_postts(sts);
>
> Additional thought while testing on my stm32mp2:
>
> Would a plain readl() for PTP_STNSR be enough? readl() completes before
> a following delay loop, which is the counter read postts does. That would
> drop both barriers, like igb/ice/bnxt. Fine either way though, macb has
> the same rmb() pattern.
>
> Maxime (Chevallier), what do you think?
I agree yes, I was also wondering about just going to non-relaxed accessor
and drop the barriers.
Maxime
>
>> [...]
>
> Thanks,
> Nicolai
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