netdev - Re: [PATCH net v2 2/2] phy: aquantia: Determine rate adaptation support from registers

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Date:   Tue, 29 Nov 2022 11:29:39 -0500
From:   Sean Anderson <sean.anderson@...o.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
        Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Tim Harvey <tharvey@...eworks.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net v2 2/2] phy: aquantia: Determine rate adaptation
 support from registers

On 11/29/22 11:17, Russell King (Oracle) wrote:
> On Tue, Nov 29, 2022 at 10:56:56AM -0500, Sean Anderson wrote:
>> On 11/28/22 19:42, Russell King (Oracle) wrote:
>> > On Mon, Nov 28, 2022 at 07:21:56PM -0500, Sean Anderson wrote:
>> >> On 11/28/22 18:22, Russell King (Oracle) wrote:
>> >> > This doesn't make any sense. priv->supported_speeds is the set of speeds
>> >> > read from the PMAPMD. The only bits that are valid for this are the
>> >> > MDIO_PMA_SPEED_* definitions, but teh above switch makes use of the
>> >> > MDIO_PCS_SPEED_* definitions. To see why this is wrong, look at these
>> >> > two definitions:
>> >> > 
>> >> > #define MDIO_PMA_SPEED_10               0x0040  /* 10M capable */
>> >> > #define MDIO_PCS_SPEED_2_5G             0x0040  /* 2.5G capable */
>> >> > 
>> >> > Note that they are the same value, yet above, you're testing for bit 6
>> >> > being clear effectively for both 10M and 2.5G speeds. I suspect this
>> >> > is *not* what you want.
>> >> > 
>> >> > MDIO_PMA_SPEED_* are only valid for the PMAPMD MMD (MMD 1).
>> >> > MDIO_PCS_SPEED_* are only valid for the PCS MMD (MMD 3).
>> >> 
>> >> Ugh. I almost noticed this from the register naming...
>> >> 
>> >> Part of the problem is that all the defines are right next to each other
>> >> with no indication of what you just described.
>> > 
>> > That's because they all refer to the speed register which is at the same
>> > address, but for some reason the 802.3 committees decided to make the
>> > register bits mean different things depending on the MMD. That's why the
>> > definition states the MMD name in it.
>> 
>> Well, then it's really a different register per MMD (and therefore the
>> definitions should be better separated). Grouping them together implies
>> that they share bits, when they do not (except for the 10G bit).
> 
> What about bits that are shared amongst the different registers.
> Should we have multiple definitions for the link status bit in _all_
> the different MMDs, despite it being the same across all status 1
> registers?

No, but for registers which are 95% difference we should at least separate
them and add a comment.

> Clause 45 is quite a trainwreck when it comes to these register
> definitions.

Maybe they should have randomized the bit orders in the first place to discourage this sort of thing :)

> As I've stated, there is a pattern to the naming. Understand it,
> and it isn't confusing.
> 

I don't have a problem with the naming, just the organization of the
source file.

--Sean
--Sean