linux-kernel - Re: [PATCH net-next 1/2] net: pcs: xpcs: enable skip xPCS soft reset

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Date:   Wed, 11 Aug 2021 07:55:29 +0800
From:   Wong Vee Khee <vee.khee.wong@...ux.intel.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Voon Weifeng <weifeng.voon@...el.com>,
        Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>,
        Vladimir Oltean <olteanv@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] net: pcs: xpcs: enable skip xPCS soft reset

Hi Andrew,
On Mon, Aug 09, 2021 at 03:35:09PM +0200, Andrew Lunn wrote:
> On Mon, Aug 09, 2021 at 06:22:28PM +0800, Wong Vee Khee wrote:
> > From: Michael Sit Wei Hong <michael.wei.hong.sit@...el.com>
> > 
> > Unlike any other platforms, Intel AlderLake-S uses Synopsys SerDes where
> > all the SerDes PLL configurations are controlled by the xPCS at the BIOS
> > level. If the driver perform a xPCS soft reset on initialization, these
> > settings will be switched back to the power on reset values.
> > 
> > This changes the xpcs_create function to take in an additional argument
> > to check if the platform request to skip xPCS soft reset during device
> > initialization.
> 
> Why not just call into the BIOS and ask it to configure the SERDES?
> Isn't that what ACPI is all about, hiding the details from the OS? Or
> did the BIOS writers not add a control method to do this?
> 
>     Andrew

BIOS does configured the SerDes. The problem here is that all the
configurations done by BIOS are being reset at xpcs_create().

We would want user of the pcs-xpcs module (stmmac, sja1105) to have
control whether or not we need to perform to the soft reset in the
xpcs_create() call.

Hope that explained.

Regards,
 VK