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

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Message-ID: <6134025a-5262-bf90-72cf-9a1de7878546@seco.com>
Date:   Tue, 29 Nov 2022 11:57:36 -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 11:46, Russell King (Oracle) wrote:
> On Tue, Nov 29, 2022 at 11:29:39AM -0500, Sean Anderson wrote:
>> 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.
> 
> The organisation is sane. There are some shared bits in the SPEED
> register between different MMDs.
> 
> If we separate the PMA and PCS with a blink line, do we then seperate
> the register groups with two blank lines? No, people will complain
> about that (they already do if you think about doing that in source
> files.)
> 
> Sorry, but... one has to pay attention to the whole of the macro name,
> not just the last few characters... and think "is something that
> contains "_PCS_" in its name really suitable for use with a PMA/PMD
> MMD register when there's a PCS MMD? Now let me think... umm. no.
> 

Well, what I had in mind was

diff --git a/include/uapi/linux/mdio.h b/include/uapi/linux/mdio.h
index 75b7257a51e1..d700e9e886b9 100644
--- a/include/uapi/linux/mdio.h
+++ b/include/uapi/linux/mdio.h
@@ -127,16 +127,36 @@
 #define MDIO_AN_STAT1_PAGE             0x0040  /* Page received */
 #define MDIO_AN_STAT1_XNP              0x0080  /* Extended next page status */
 
-/* Speed register. */
+/* Speed register common. */
 #define MDIO_SPEED_10G                 0x0001  /* 10G capable */
+
+/* PMA/PMD Speed register. */
+#define MDIO_PMA_SPEED_10G             MDIO_SPEED_10G
 #define MDIO_PMA_SPEED_2B              0x0002  /* 2BASE-TL capable */
 #define MDIO_PMA_SPEED_10P             0x0004  /* 10PASS-TS capable */
 #define MDIO_PMA_SPEED_1000            0x0010  /* 1000M capable */
 #define MDIO_PMA_SPEED_100             0x0020  /* 100M capable */
 #define MDIO_PMA_SPEED_10              0x0040  /* 10M capable */
+#define MDIO_PMA_SPEED_10G1G           0x0080  /* 10/1G capable */
+#define MDIO_PMA_SPEED_40G             0x0100  /* 40G capable */
+#define MDIO_PMA_SPEED_100G            0x0200  /* 100G capable */
+#define MDIO_PMA_SPEED_10GP            0x0400  /* 10GPASS-XR capable */
+#define MDIO_PMA_SPEED_25G             0x0800  /* 25G capable */
+#define MDIO_PMA_SPEED_200G            0x1000  /* 200G capable */
+#define MDIO_PMA_SPEED_2_5G            0x2000  /* 2.5G capable */
+#define MDIO_PMA_SPEED_5G              0x4000  /* 5G capable */
+#define MDIO_PMA_SPEED_400G            0x8000  /* 400G capable */
+
+/* PCS et al. Speed register. */
+#define MDIO_PCS_SPEED_10G             MDIO_SPEED_10G
 #define MDIO_PCS_SPEED_10P2B           0x0002  /* 10PASS-TS/2BASE-TL capable */
+#define MDIO_PCS_SPEED_40G             0x0004  /* 450G capable */
+#define MDIO_PCS_SPEED_100G            0x0008  /* 100G capable */
+#define MDIO_PCS_SPEED_25G             0x0010  /* 25G capable */
 #define MDIO_PCS_SPEED_2_5G            0x0040  /* 2.5G capable */
 #define MDIO_PCS_SPEED_5G              0x0080  /* 5G capable */
+#define MDIO_PCS_SPEED_200G            0x0100  /* 200G capable */
+#define MDIO_PCS_SPEED_400G            0x0200  /* 400G capable */
 
 /* Device present registers. */
 #define MDIO_DEVS_PRESENT(devad)       (1 << (devad))

Really, these registers have almost nothing in common except their concept
and sub-address.

On another note: is BIT() allowed in uapi headers?

--Sean