linux-kernel - Re: [PATCH v2 2/2] phy: nxp-c45-tja11xx: read the tx timestamp without lock

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Date:   Thu, 23 Dec 2021 12:24:17 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     "Radu Pirea (NXP OSS)" <radu-nicolae.pirea@....nxp.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        christian.herber@....com, andrew@...n.ch, hkallweit1@...il.com,
        linux@...linux.org.uk, davem@...emloft.net, kuba@...nel.org
Subject: Re: [PATCH v2 2/2] phy: nxp-c45-tja11xx: read the tx timestamp
 without lock

On Wed, Dec 22, 2021 at 11:34:53PM +0200, Radu Pirea (NXP OSS) wrote:
> Reading the tx timestamps can be done in parallel with adjusting the LTC
> value.
> 
> Calls to nxp_c45_get_hwtxts() are always serialised. If the phy
> interrupt is enabled, .do_aux_work() will not call nxp_c45_get_hwtxts.

Reviewing the code, I see what you mean.  However, the serialization
is completely non-obvious, and future changes to the driver could
easily spoil the implicit serialization.  Given that the mutex is not
highly contended, I suggest dropping this patch in order to
future-proof the driver.

Thanks,
Richard