linux-kernel - Re: [PATCH v2 3/3] net: ethernet: fec: fix refclk enable for SMSC LAN8710/20

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Message-ID: <30a94c72-2345-0649-6682-4826d31c3285@skidata.com>
Date:   Mon, 20 Nov 2017 13:55:14 +0100
From:   Richard Leitner <richard.leitner@...data.com>
To:     Andy Duan <fugang.duan@....com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>
CC:     Richard Leitner <dev@...l1n.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v2 3/3] net: ethernet: fec: fix refclk enable for SMSC
 LAN8710/20

On 11/20/2017 11:35 AM, Andy Duan wrote:
> From: Richard Leitner <richard.leitner@...data.com> Sent: Monday, November 20, 2017 5:57 PM
>> To: Andy Duan <fugang.duan@....com>; f.fainelli@...il.com;
>> andrew@...n.ch
>> Cc: Richard Leitner <dev@...l1n.net>; netdev@...r.kernel.org; linux-
>> kernel@...r.kernel.org
>> Subject: Re: [PATCH v2 3/3] net: ethernet: fec: fix refclk enable for SMSC
>> LAN8710/20
>>
>>
>> On 11/20/2017 10:47 AM, Andy Duan wrote:
>>> From: Richard Leitner <dev@...l1n.net> Sent: Monday, November 20, 2017
>>> 4:34 PM
>>>> To: f.fainelli@...il.com; Andy Duan <fugang.duan@....com>;
>>>> andrew@...n.ch
>>>> Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
>>>> richard.leitner@...data.com
>>>> Subject: [PATCH v2 3/3] net: ethernet: fec: fix refclk enable for
>>>> SMSC
>>>> LAN8710/20
>>>>
>>>> From: Richard Leitner <richard.leitner@...data.com>
>>>>
>>>> Some PHYs (for example the SMSC LAN8710/LAN8720) doesn't allow
>>>> turning the refclk on and off again during operation (according to their
>> datasheet).
>>>> Nonetheless exactly this behaviour was introduced for power saving
>>>> reasons by commit e8fcfcd5684a ("net: fec: optimize the clock
>>>> management to save power").
>>>> Therefore after enabling the refclk we detect if an affected PHY is
>>>> attached. If so reset and initialize it again.
>> ...
>>
>>>> +static int fec_enet_clk_ref_enable_reset_phy_quirk(struct net_device
>>>> +*ndev) {
>>>> +	struct phy_device *phy_dev = ndev->phydev;
>>>> +	u32 real_phy_id;
>>>> +	int ret;
>>>> +
>>>> +	/* some PHYs need a reset after the refclk was enabled, so we
>>>> +	 * reset them here
>>>> +	 */
>>>> +	if (!phy_dev)
>>>> +		return 0;
>>>> +	if (!phy_dev->drv)
>>>> +		return 0;
>>>> +	real_phy_id = phy_dev->drv->phy_id & phy_dev->drv->phy_id_mask;
>>>> +	switch (real_phy_id) {
>>>> +	case 0x0007c0f0: /* SMSC LAN8710/LAN8720 */
>>> Don't hard code here...
>>> I believe there have many other phys also do such operation, hardcode is
>> unacceptable...
>>> And these code can be put into phy_device.c as common interface.
>> Ok. Thank you for the feedback.
>> So it would be fine to hardcode the affected phy_id's in a common function in
>> phy_device.c?
>>
>>
>> Another possible solution that came to my mind is to add a flag called
>> something like "PHY_RST_AFTER_CLK_EN" to the flags variable in struct
>> phy_driver. This flag could then be set in the smsc PHY driver for affected
>> PHYs.
>>
>> Then instead of comparing the phy_id in the MAC driver this flag could be
>> checked:
>>
>> if (phydev->drv->flags & PHY_RST_AFTER_CLK_EN) {
>>    ret = fec_reset_phy(ndev);
>>    ...
>> }
>>
>> Would checking the flag be OK in fec_main.c?
> Yes, it is better than previous solution.
> But add new common API in phy_device.c is much better like: 
> 1. add a flag called "PHY_RST_AFTER_CLK_EN" to the flags variable in struct phy_driver,  all phy driver that need reset can set the flag.

OK.

> 2. add new common api interface phy_reset_after_clk_enable() in phy_device.c driver

OK. But see below...

> 3. add reset gpio descriptor for common phy device driver. 

... if I understood it correctly the patch called "Teach phylib
hard-resetting devices" by Geert and Sergei is exactly doing this:
	https://patchwork.ozlabs.org/cover/828503/
	https://lkml.org/lkml/2017/10/20/166

So I'll implement the phy_reset_after_clk_enable function atop of this
patch-set and add a note that my patch-series depends on it. Would that
be OK?

> 4. then any mac driver can directly call the common interface .phy_reset_after_clk_enable().

Sounds reasonable :-)

> 
> That is only my suggestion, maybe there have better idea.
> Thanks.
> 

Thanks for your quick feedback.

regards
Richard.L