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

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Message-ID: <20250821180247.29d0f4b3@kernel.org>
Date: Thu, 21 Aug 2025 18:02:47 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Manivannan Sadhasivam <mani@...nel.org>, 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 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.

Exporting read-only clocks from another processor is not what PTP
is for.