Re: [PATCH net-next v3 4/4] net: fec: add phy_reset_after_clk_enable() support

Richard Leitner
2017-12-06T08:23:25Z

Hi Andy,

On 12/06/2017 02:50 AM, Andy Duan wrote:
> From: Richard Leitner <dev@g0hl1n.net> Sent: Tuesday, December 05, 2017 9:26 PM
>> 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 add support for the phy_reset_after_clk_enable function from
>> phylib to mitigate this issue.

...

>> diff --git a/drivers/net/ethernet/freescale/fec_main.c
>> b/drivers/net/ethernet/freescale/fec_main.c
>> index 610573855213..8c3d0fb7db20 100644
>> --- a/drivers/net/ethernet/freescale/fec_main.c
>> +++ b/drivers/net/ethernet/freescale/fec_main.c
>> @@ -1862,6 +1862,8 @@ static int fec_enet_clk_enable(struct net_device
>> *ndev, bool enable)
>> ret = clk_prepare_enable(fep->clk_ref);
>> if (ret)
>> goto failed_clk_ref;
>> +
>> + phy_reset_after_clk_enable(ndev->phydev);
>> } else {
>> clk_disable_unprepare(fep->clk_ahb);
>> clk_disable_unprepare(fep->clk_enet_out);
>> @@ -2860,6 +2862,11 @@ fec_enet_open(struct net_device *ndev)
>> if (ret)
>> goto err_enet_mii_probe;
>>
>> + /* reset phy if needed here, due to the fact this is the first time we
>> + * have the net_device to phy_driver link
>> + */
>> + phy_reset_after_clk_enable(ndev->phydev);
>> +
>
> The patch series look better.
> But why does it need to reset phy here since phy already is hard reset after clock enable.

The problem here is that in fec_enet_open() the fec_enet_clk_enable()
call is done before the phy is probed. Therefore (as mentioned in the
comment) there's no link from the net_device (ndev) to the phy_driver
(which holds the flags).

Any suggestions for a better solution are highly appreciated here! Thanks!

regards;Richard.L