linux-kernel - Re: [PATCH net] net: lan966x: Fix the initialization of taprio

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Message-ID: <20251119171714.qrzxeufuchci5xfq@DEN-DL-M31836.microchip.com>
Date: Wed, 19 Nov 2025 18:17:14 +0100
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: Andrew Lunn <andrew@...n.ch>
CC: <UNGLinuxDriver@...rochip.com>, <andrew+netdev@...n.ch>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <richardcochran@...il.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: lan966x: Fix the initialization of taprio

The 11/19/2025 15:26, Andrew Lunn wrote:
> 
> On Wed, Nov 19, 2025 at 09:26:46AM +0100, Horatiu Vultur wrote:
> > The 11/18/2025 20:20, Andrew Lunn wrote:
> >
> > Hi Andrew,
> >
> > >
> > > On Mon, Nov 17, 2025 at 03:43:09PM +0100, Horatiu Vultur wrote:
> > > > To initialize the taprio block in lan966x, it is required to configure
> > > > the register REVISIT_DLY. The purpose of this register is to set the
> > > > delay before revisit the next gate and the value of this register depends
> > > > on the system clock. The problem is that the we calculated wrong the value
> > > > of the system clock period in picoseconds. The actual system clock is
> > > > ~165.617754MHZ and this correspond to a period of 6038 pico seconds and
> > > > not 15125 as currently set.
> > >
> > > Is the system clock available as a linux clock? Can you do a
> > > clk_get_rate() on it?
> >
> > Unfortunetly, I can not do clk_get_rate because in the device tree for the
> > switch node I don't have any clocks property. And maybe that is the
> > problem because I have the system clock (sys_clk) in the lan966x.dtsi
> > file. But if I go this way then I need add a bigger changeset and add
> > it to multiple kernel trees which complicate the things.
> > So maybe I should not change this patch and then create another one
> > targeting net-next where I can start using clk_get_rate()
> 
> This is fine as is. But maybe rather than use the magic number, add a
> #defines for the system clock rate, and convert to pico seconds in the
> code, and let the compiler do it at compile time. The code then
> documents what is going on.

Yes, I will add a define for system clock.
I will do it as suggested by Eric.

> 
>         Andrew

-- 
/Horatiu