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Date: Tue, 31 Mar 2020 16:53:50 +0100 From: Russell King - ARM Linux admin <linux@...linux.org.uk> To: David Jander <david@...tonic.nl> Cc: Florian Fainelli <f.fainelli@...il.com>, Oleksij Rempel <o.rempel@...gutronix.de>, Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org, Sascha Hauer <s.hauer@...gutronix.de>, linux-kernel@...r.kernel.org, Fabio Estevam <festevam@...il.com>, linux-imx@....com, kernel@...gutronix.de, Shawn Guo <shawnguo@...nel.org>, linux-arm-kernel@...ts.infradead.org, Heiner Kallweit <hkallweit1@...il.com> Subject: Re: [PATCH v2] ARM: imx: allow to disable board specific PHY fixups On Tue, Mar 31, 2020 at 05:41:03PM +0200, David Jander wrote: > > Dear Russell, > > On Tue, 31 Mar 2020 10:36:49 +0100 > Russell King - ARM Linux admin <linux@...linux.org.uk> wrote: > > > On Tue, Mar 31, 2020 at 10:44:59AM +0200, David Jander wrote: > > > On Mon, 30 Mar 2020 18:41:14 +0100 > > > Russell King - ARM Linux admin <linux@...linux.org.uk> wrote: > > > > > > > On Mon, Mar 30, 2020 at 10:33:03AM -0700, Florian Fainelli wrote: > > > > > > > > > > > > > > > On 3/29/2020 10:26 PM, Oleksij Rempel wrote: > > > > > > Hi Andrew, > > > > > > > > > > > > On Sun, Mar 29, 2020 at 05:08:54PM +0200, Andrew Lunn wrote: > > > > > >> On Sun, Mar 29, 2020 at 01:04:57PM +0200, Oleksij Rempel wrote: > > > > > >> > > > > > >> Hi Oleksij > > > > > >> > > > > > >>> +config DEPRECATED_PHY_FIXUPS > > > > > >>> + bool "Enable deprecated PHY fixups" > > > > > >>> + default y > > > > > >>> + ---help--- > > > > > >>> + In the early days it was common practice to configure PHYs by adding a > > > > > >>> + phy_register_fixup*() in the machine code. This practice turned out to > > > > > >>> + be potentially dangerous, because: > > > > > >>> + - it affects all PHYs in the system > > > > > >>> + - these register changes are usually not preserved during PHY reset > > > > > >>> + or suspend/resume cycle. > > > > > >>> + - it complicates debugging, since these configuration changes were not > > > > > >>> + done by the actual PHY driver. > > > > > >>> + This option allows to disable all fixups which are identified as > > > > > >>> + potentially harmful and give the developers a chance to implement the > > > > > >>> + proper configuration via the device tree (e.g.: phy-mode) and/or the > > > > > >>> + related PHY drivers. > > > > > >> > > > > > >> This appears to be an IMX only problem. Everybody else seems to of got > > > > > >> this right. There is no need to bother everybody with this new > > > > > >> option. Please put this in arch/arm/mach-mxs/Kconfig and have IMX in > > > > > >> the name. > > > > > > > > > > > > Actually, all fixups seems to do wring thing: > > > > > > arch/arm/mach-davinci/board-dm644x-evm.c:915: phy_register_fixup_for_uid(LXT971_PHY_ID, LXT971_PHY_MASK, > > > > > > > > > > > > Increased MII drive strength. Should be probably enabled by the PHY > > > > > > driver. > > > > > > > > > > > > arch/arm/mach-imx/mach-imx6q.c:167: phy_register_fixup_for_uid(PHY_ID_KSZ9021, MICREL_PHY_ID_MASK, > > > > > > arch/arm/mach-imx/mach-imx6q.c:169: phy_register_fixup_for_uid(PHY_ID_KSZ9031, MICREL_PHY_ID_MASK, > > > > > > arch/arm/mach-imx/mach-imx6q.c:171: phy_register_fixup_for_uid(PHY_ID_AR8031, 0xffffffef, > > > > > > arch/arm/mach-imx/mach-imx6q.c:173: phy_register_fixup_for_uid(PHY_ID_AR8035, 0xffffffef, > > > > > > > > As far as I'm concerned, the AR8035 fixup is there with good reason. > > > > It's not just "random" but is required to make the AR8035 usable with > > > > the iMX6 SoCs. Not because of a board level thing, but because it's > > > > required for the AR8035 to be usable with an iMX6 SoC. > > > > > > I have checked with the datasheet of the AR8035, and AFAICS, what the code > > > does is this: > > > > > > - Disable the SmartEEE feature of the phy. The comment in the code implies > > > that for some reason it doesn't work, but the reason itself is not given. > > > Anyway, disabling SmartEEE should IMHO opinion be controlled by a DT > > > setting. There is no reason to believe this problem is specific to the > > > i.MX6. Besides, it is a feature of the phy, so it seems logical to expose > > > that via the DT. Once that is done, it has no place here. > > > > > > - Set the external clock output to 125MHz. This is needed because the i.MX6 > > > needs a 125MHz reference clock input. But it is not a requirement to use > > > this output. It is perfectly fine and possible to design a board that uses > > > an external oscillator for this. It is also possible that an i.MX6 design > > > has such a phy connected to a MAC behind a switch or some other interface. > > > Independent of i.MX6 this setting can also be necessary for other hardware > > > designs, based on different SoC's. In summary, this is a feature of the > > > specific hardware design at hand, and has nothing to do with the i.MX6 > > > specifically. This should definitely be exposed through the DT and not be > > > here. > > > > > > - Enable TXC delay. To clarify, the RGMII specification version 1 specified > > > that the RXC and TXC traces should be routed long enough to introduce a > > > certain delay to the clock signal, or the delay should be introduced via > > > other means. In a later version of the spec, a provision was given for MAC > > > or PHY devices to generate this delay internally. The i.MX6 MAC interface > > > is unable to generate the required delay internally, so it has to be taken > > > care of either by the board layout, or by the PHY device. This is the > > > crucial point: The amount of delay set by the PHY delay register depends on > > > the board layout. It should NEVER be hard-coded in SoC setup code. The > > > correct way is to specify it in the DT. Needless to say that this too, > > > isn't i.MX6-specific. > > > > > > > So, having it registered by the iMX6 SoC code is entirely logical and > > > > correct. > > > > > > I'm afraid I don't agree. See above. This code really should never have been > > > here. It is not i.MX6-specific as I pointed out above, nor is it necessarily > > > applicable to all i.MX6 boards that use those phy devices. > > > > Then we will have to agree to disagree, sorry. > > Please forgive me if I am appearing a bit stubborn. > If it is not too much to ask, I would really like to know where my reasoning > is wrong? > Maybe you can explain to me how to solve the following real-life conflict that > this introduces: > > Suppose we have a board with an i.MX6Q and a KSZ9031 connected to it. Suppose > I now take a USB stick with a LAN7800 ethernet chip and a KSZ9031 PHY. These > USB sticks do exist, and it does not seem unthinkable to me that one would > connect them to such an i.MX6 system in order to get a second LAN port. Thanks. I've already covered how this can be delt with in some code I've posted in this thread. Therefore, I have nothing further to add to this point, apart from pointing out that I've provided a solution so as far as I'm concerned, it's entirely solvable, and warrants no further argument. Maybe a discussion about solutions would be appropriate, but merely re-raising the same point while ignoring proposed solutions is not a productive way forward. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up
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