netdev - Re: [PATCH net-next 0/3] net: pcs: altera-tse: simplify and clean-up the driver

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Date:   Mon, 28 Nov 2022 09:39:56 +0100
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     davem@...emloft.net, Rob Herring <robh+dt@...nel.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        thomas.petazzoni@...tlin.com, Andrew Lunn <andrew@...n.ch>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 0/3] net: pcs: altera-tse: simplify and
 clean-up the driver

Hello Russell,

On Sun, 27 Nov 2022 17:34:53 +0000
"Russell King (Oracle)" <linux@...linux.org.uk> wrote:

> On Fri, Nov 25, 2022 at 02:17:58PM +0100, Maxime Chevallier wrote:
> > Hello everyone,
> > 
> > This small series does a bit of code cleanup in the altera TSE pcs
> > driver, removong unused register definitions, handling 1000BaseX
> > speed configuration correctly according to the datasheet, and
> > making use of proper poll_timeout helpers.
> > 
> > No functional change is introduced.
> > 
> > Best regards,
> > 
> > Maxime
> > 
> > Maxime Chevallier (3):
> >   net: pcs: altera-tse: use read_poll_timeout to wait for reset
> >   net: pcs: altera-tse: don't set the speed for 1000BaseX
> >   net: pcs: altera-tse: remove unnecessary register definitions  
> 
> Hi Maxime,
> 
> Please can you check the link timer settings:
> 
>         /* Set link timer to 1.6ms, as per the MegaCore Function User
> Guide */ tse_pcs_write(tse_pcs, SGMII_PCS_LINK_TIMER_0, 0x0D40);
>         tse_pcs_write(tse_pcs, SGMII_PCS_LINK_TIMER_1, 0x03);
> 
> This is true for Cisco SGMII mode - which is specified to use a 1.6ms
> link timer, but 1000baseX is specified by 802.3 to use a 10ms link
> timer interval, so this is technically incorrect for 1000base-X. So,
> if the MegaCore Function User Guide specifies 1.6ms for everything, it
> would appear to contradict 802.3.
> 
> From what I gather from the above, the link timer uses a value of
> 200000 for 1.6ms, which means it is using a 8ns clock period or
> 125MHz.
> 
> If you wish to correct the link timer, you can use this:
> 
> 	int link_timer;
> 
> 	link_timer = phylink_get_link_timer_ns(interface) / 8;
> 	if (link_timer > 0) {
> 		tse_pcs_write(tse_pcs, SGMII_PCS_LINK_TIMER_0,
> link_timer); tse_pcs_write(tse_pcs, SGMII_PCS_LINK_TIMER_1,
> link_timer >> 16); }
> 
> so that it gets set correctly depending on 'interface'.
> phylink_get_link_timer_ns() is an inline static function, so you
> should end up with the above fairly optimised, not that it really
> matters. Also worth documenting that the "8" there is 125MHz in
> nanoseconds - maybe in a similar way to pcs-lynx does.

Ouh that's perfect, thanks !

> It does look like this Altera TSE PCS is very similar to pcs-lynx,
> maybe there's a possibility of refactoring both drivers to share
> code?

Indeed, I've some patches I'm testing to port pcs-lynx to regmap then
do the merge. The one thing that would differ is the reset
handling in the TSE driver, since we need to perform it at every
configuration change basically. But that's not worth having duplicate
drivers just for that, I agree.

I'll post that merge when I'll have the chance to give it a more
thourough test.

Thanks,

Maxime