linux-kernel - Re: [PATCH 5/5] bus: mhi: host: mhi_phc: Add support for PHC over MHI

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Message-ID: <j5kwwz4z635tqahu7kfs53t3ugs346ustz625xx2tjl36rgwwl@rx26xd76qbtj>
Date: Wed, 26 Nov 2025 19:34:45 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, 
	Richard Cochran <richardcochran@...il.com>, mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, taniya.das@....qualcomm.com, 
	imran.shaik@....qualcomm.com, quic_vbadigan@...cinc.com, quic_mrana@...cinc.com
Subject: Re: [PATCH 5/5] bus: mhi: host: mhi_phc: Add support for PHC over MHI

On Thu, Aug 21, 2025 at 06:02:47PM -0700, Jakub Kicinski wrote:
> On Mon, 18 Aug 2025 12:25:50 +0530 Krishna Chaitanya Chundru wrote:
> > This patch introduces the MHI PHC (PTP Hardware Clock) driver, which
> > registers a PTP (Precision Time Protocol) clock and communicates with
> > the MHI core to get the device side timestamps. These timestamps are
> > then exposed to the PTP subsystem, enabling precise time synchronization
> > between the host and the device.
> 
> > +static struct ptp_clock_info qcom_ptp_clock_info = {
> > +	.owner    = THIS_MODULE,
> > +	.gettimex64 =  qcom_ptp_gettimex64,
> > +};
> 
> Yet another device to device clock sync driver. Please see the
> discussion here:
> https://lore.kernel.org/all/20250815113814.5e135318@kernel.org/
> I think we have a consensus within the community that we should 
> stop cramming random clocks into the PTP subsystem.
> 

I agree with you that this clock is not a PTP clock. Looking at the other
discussion you pointed out above, I guess it is the time to come up with a new
framework that exposes the device clock to the host.

But my worry is that the new framework will look a lot like PTP Hardware Clock
(PHC) (atleast for the clock part) and will end up supporting the same userspace
tooling like phc2sys.

- Mani

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