Re: [PATCH 01/20] net: phy: realtek: Fix events detection failure in LPI mode

[Heiner Kallweit <hkallweit1@gmail.com>]

On 09.02.2021 11:15, Serge Semin wrote:
> On Mon, Feb 08, 2021 at 09:14:02PM +0100, Heiner Kallweit wrote:
>> On 08.02.2021 15:03, Serge Semin wrote:
>>> It has been noticed that RTL8211E PHY stops detecting and reporting events
>>> when EEE is successfully advertised and RXC stopping in LPI is enabled.
>>> The freeze happens right after 3.0.10 bit (PC1R "Clock Stop Enable"
>>> register) is set. At the same time LED2 stops blinking as if EEE mode has
>>> been disabled. Notably the network traffic still flows through the PHY
>>> with no obvious problem. Anyway if any MDIO read procedure is performed
>>> after the "RXC stop in LPI" mode is enabled PHY gets to be unfrozen, LED2
>>> starts blinking and PHY interrupts happens again. The problem has been
>>> noticed on RTL8211E PHY working together with DW GMAC 3.73a MAC and
>>> reporting its event via a dedicated IRQ signal. (Obviously the problem has
>>> been unnoticed in the polling mode, since it gets naturally fixed by the
>>> periodic MDIO read procedure from the PHY status register - BMSR.)
>>>
>>> In order to fix that problem we suggest to locally re-implement the MMD
>>> write method for RTL8211E PHY and perform a dummy read right after the
>>> PC1R register is accessed to enable the RXC stopping in LPI mode.
>>>
>>> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
>>> ---
>>>  drivers/net/phy/realtek.c | 37 +++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 37 insertions(+)
>>>
>>> diff --git a/drivers/net/phy/realtek.c b/drivers/net/phy/realtek.c
>>> index 99ecd6c4c15a..cbb86c257aae 100644
>>> --- a/drivers/net/phy/realtek.c
>>> +++ b/drivers/net/phy/realtek.c
>>> @@ -559,6 +559,42 @@ static int rtl822x_write_mmd(struct phy_device *phydev, int devnum, u16 regnum,
>>>  	return ret;
>>>  }
>>>  
>>> +static int rtl8211e_write_mmd(struct phy_device *phydev, int devnum, u16 regnum,
>>> +			      u16 val)
>>> +{
>>> +	int ret;
>>> +
>>> +	/* Write to the MMD registers by using the standard control/data pair.
>>> +	 * The only difference is that we need to perform a dummy read after
>>> +	 * the PC1R.CLKSTOP_EN bit is set. It's required to workaround an issue
>>> +	 * of a partial core freeze so LED2 stops blinking in EEE mode, PHY
>>> +	 * stops detecting the link change and raising IRQs until any read from
>>> +	 * its registers performed. That happens only if and right after the PHY
>>> +	 * is enabled to stop RXC in LPI mode.
>>> +	 */
>>> +	ret = __phy_write(phydev, MII_MMD_CTRL, devnum);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	ret = __phy_write(phydev, MII_MMD_DATA, regnum);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	ret = __phy_write(phydev, MII_MMD_CTRL, devnum | MII_MMD_CTRL_NOINCR);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>
> 
>> Nice analysis. Alternatively to duplicating this code piece we could
>> export mmd_phy_indirect(). But up to you.
> 
> I also considered creating a generic method to access the MMD
> registers of a generic PHY, something like phy_read()/phy_write(), but
> for MMD (alas just exporting mmd_phy_indirect() would not be enough).
> But as I see it such methods need to be created only after we get to
> have at least several places with duplicating direct MMD-read/write
> patterns. Doing that just for a single place seems redundant. Anyway it's
> up to maintainers to decide whether they want to see a generic part
> of the phy_read_mmd()/phy_write_mmd() methods being detached and
> exported as something like genphy_{read,write}_mmd() methods. I can do
> that in v2 if you ask me to.
> 
Right, adding something like a genphy_{read,write}_mmd() doesn't make
too much sense for now. What I meant is just exporting mmd_phy_indirect().
Then you don't have to open-code the first three steps of a mmd read/write.
And it requires no additional code in phylib.
But that's not at all a showstopper here.

> -Sergey
> 
>>
>>> +	ret = __phy_write(phydev, MII_MMD_DATA, val);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	if (devnum == MDIO_MMD_PCS && regnum == MDIO_CTRL1 &&
>>> +	    val & MDIO_PCS_CTRL1_CLKSTOP_EN)
>>> +		ret =  __phy_read(phydev, MII_MMD_DATA);
>>> +
>>> +	return ret < 0 ? ret : 0;
>>> +}
>>> +
>>>  static int rtl822x_get_features(struct phy_device *phydev)
>>>  {
>>>  	int val;
>>> @@ -725,6 +761,7 @@ static struct phy_driver realtek_drvs[] = {
>>>  		.resume		= genphy_resume,
>>>  		.read_page	= rtl821x_read_page,
>>>  		.write_page	= rtl821x_write_page,
>>> +		.write_mmd	= rtl8211e_write_mmd,
>>>  	}, {
>>>  		PHY_ID_MATCH_EXACT(0x001cc916),
>>>  		.name		= "RTL8211F Gigabit Ethernet",
>>>
>>