netdev - Re: [PATCH net 1/3] lan78xx: PHY DSP registers initialization to address EEE link drop issues with long cables

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Date:   Fri, 06 Apr 2018 11:21:58 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     andrew@...n.ch
Cc:     raghuramchary.jallipalli@...rochip.com, netdev@...r.kernel.org,
        unglinuxdriver@...rochip.com, woojung.huh@...rochip.com
Subject: Re: [PATCH net 1/3] lan78xx: PHY DSP registers initialization to
 address EEE link drop issues with long cables

From: Andrew Lunn <andrew@...n.ch>
Date: Fri, 6 Apr 2018 16:43:42 +0200

> On Fri, Apr 06, 2018 at 11:42:02AM +0530, Raghuram Chary J wrote:
>> The patch is to configure DSP registers of PHY device
>> to handle Gbe-EEE failures with >40m cable length.
>> 
>> Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver")
>> Signed-off-by: Raghuram Chary J <raghuramchary.jallipalli@...rochip.com>
>> ---
>>  drivers/net/phy/microchip.c  | 123 ++++++++++++++++++++++++++++++++++++++++++-
>>  include/linux/microchipphy.h |   8 +++
>>  2 files changed, 130 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/net/phy/microchip.c b/drivers/net/phy/microchip.c
>> index 0f293ef28935..174ae9808722 100644
>> --- a/drivers/net/phy/microchip.c
>> +++ b/drivers/net/phy/microchip.c
>> @@ -20,6 +20,7 @@
>>  #include <linux/ethtool.h>
>>  #include <linux/phy.h>
>>  #include <linux/microchipphy.h>
>> +#include <linux/delay.h>
>>  
>>  #define DRIVER_AUTHOR	"WOOJUNG HUH <woojung.huh@...rochip.com>"
>>  #define DRIVER_DESC	"Microchip LAN88XX PHY driver"
>> @@ -66,6 +67,107 @@ static int lan88xx_suspend(struct phy_device *phydev)
>>  	return 0;
>>  }
>>  
>> +static void lan88xx_TR_reg_set(struct phy_device *phydev, u16 regaddr,
>> +			       u32 data)
>> +{
>> +	int val;
>> +	u16 buf;
>> +
>> +	/* Get access to token ring page */
>> +	phy_write(phydev, LAN88XX_EXT_PAGE_ACCESS,
>> +		  LAN88XX_EXT_PAGE_ACCESS_TR);
> 
> Hi Raghuram
> 
> You might want to look at phy_read_paged(), phy_write_paged(), etc.
> 
> There can be race conditions with paged access.

Yep, so something like:

static void lan88xx_TR_reg_set(struct phy_device *phydev, u16 regaddr,
			       u32 data)
{
	int save_page, val;
	u16 buf;

	save_page = phy_save_page(phydev);
	phy_write_paged(phydev, LAN88XX_EXT_PAGE_ACCESS_TR,
			LAN88XX_EXT_PAGE_TR_LOW_DATA, (data & 0xFFFF));
	phy_write_paged(phydev, LAN88XX_EXT_PAGE_ACCESS_TR,
			LAN88XX_EXT_PAGE_TR_HIGH_DATA,
			(data & 0x00FF0000) >> 16);

	/* Config control bits [15:13] of register */
	buf = (regaddr & ~(0x3 << 13));/* Clr [14:13] to write data in reg */
	buf |= 0x8000; /* Set [15] to Packet transmit */

	phy_write_paged(phydev, LAN88XX_EXT_PAGE_ACCESS_TR,
			LAN88XX_EXT_PAGE_TR_CR, buf);
	usleep_range(1000, 2000);/* Wait for Data to be written */

	val = phy_read_paged(phydev, LAN88XX_EXT_PAGE_ACCESS_TR,
			     LAN88XX_EXT_PAGE_TR_CR);
	if (!(val & 0x8000))
		pr_warn("TR Register[0x%X] configuration failed\n", regaddr);

	phy_restore_page(phydev, save_page, 0);
}

Since PHY accesses and thus things like phy_save_page() can fail, the
return type of this function should be changed to 'int' and some error
checking should be added.