linux-kernel - Re: [PATCH v2 1/2] net: phy: realtek: Add rtl8211e rx/tx delays config

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Date:   Mon, 13 May 2019 13:37:19 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Serge Semin <Sergey.Semin@...latforms.ru>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] net: phy: realtek: Add rtl8211e rx/tx delays
 config

Hello Guenter,

On Sun, May 12, 2019 at 10:41:32PM -0700, Guenter Roeck wrote:
> Hi,
> 
> On Sat, Apr 27, 2019 at 12:21:11AM +0300, Serge Semin wrote:
> > There are two chip pins named TXDLY and RXDLY which actually adds the 2ns
> > delays to TXC and RXC for TXD/RXD latching. Alas this is the only
> > documented info regarding the RGMII timing control configurations the PHY
> > provides. It turns out the same settings can be setup via MDIO registers
> > hidden in the extension pages layout. Particularly the extension page 0xa4
> > provides a register 0x1c, which bits 1 and 2 control the described delays.
> > They are used to implement the "rgmii-{id,rxid,txid}" phy-mode.
> > 
> > The hidden RGMII configs register utilization was found in the rtl8211e
> > U-boot driver:
> > https://elixir.bootlin.com/u-boot/v2019.01/source/drivers/net/phy/realtek.c#L99
> > 
> > There is also a freebsd-folks discussion regarding this register:
> > https://reviews.freebsd.org/D13591
> > 
> > It confirms that the register bits field must control the so called
> > configuration pins described in the table 12-13 of the official PHY
> > datasheet:
> > 8:6 = PHY Address
> > 5:4 = Auto-Negotiation
> > 3 = Interface Mode Select
> > 2 = RX Delay
> > 1 = TX Delay
> > 0 = SELRGV
> > 
> > Signed-off-by: Serge Semin <fancer.lancer@...il.com>
> > Reviewed-by: Andrew Lunn <andrew@...n.ch>
> 
> This patch results in a crash when running arm:ast2500-evb in qemu.
> 
> [    4.894572] [00000000] *pgd=00000000
> [    4.895329] Internal error: Oops: 80000005 [#1] ARM
> [    4.896066] CPU: 0 PID: 1 Comm: swapper Not tainted 5.1.0-09698-g1fb3b52 #1
> [    4.896364] Hardware name: Generic DT based system
> [    4.896823] PC is at 0x0
> [    4.897037] LR is at phy_select_page+0x3c/0x7c
> 
> Debugging shows that phydev->drv->write_page and phydev->drv->read_page
> are NULL, so the crash isn't entirely surprising.
> 
> What I don't understand is how this can work in the first place.
> The modified entry in realtek_drvs[] doesn't have read_page/write_page
> functions defined, yet rtl8211e_config_init() depends on it.
> What am I missing here ?
> 
> Thanks,
> Guenter

Thanks for sending the report. The problem has already been fixed in the net:
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=daf3ddbe11a2ff74c95bc814df8e5fe3201b4cb5

-Sergey