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 01:36:56 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Wong Vee Khee <vee.khee.wong@...ux.intel.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     Vivien Didelot <vivien.didelot@...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



On 8/10/2021 4:55 PM, Wong Vee Khee wrote:
> 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.

I understood Andrew's response as suggesting to introduce the ability 
for xpcs_create() to make a BIOS call which would configure the SerDes 
after xpcs_soft_reset(). That way the current xpcs_create() signature 
would remain the same, but you could easily hook any post-reset 
initialization by making an appropriate BIOS call.
-- 
Florian