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SubjectRe: [RFC] net: phy: read link status twice when phy_check_link_status()
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On 26.07.2019 11:53, Yonglong Liu wrote:
> According to the datasheet of Marvell phy and Realtek phy, the
> copper link status should read twice, or it may get a fake link
> up status, and cause up->down->up at the first time when link up.
> This happens more oftem at Realtek phy.
>
This is not correct, there is no fake link up status.
Read the comment in genphy_update_link, only link-down events
are latched. Means if the first read returns link up, then there
is no need for a second read. And in polling mode we don't do a
second read because we want to detect also short link drops.

It would be helpful if you could describe your actual problem
and whether you use polling or interrupt mode.

> I add a fake status read, and can solve this problem.
>
> I also see that in genphy_update_link(), had delete the fake
> read in polling mode, so I don't know whether my solution is
> correct.
>
> Or provide a phydev->drv->read_status functions for the phy I
> used is more acceptable?
>
> Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
> ---
> drivers/net/phy/phy.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> index ef7aa73..0c03edc 100644
> --- a/drivers/net/phy/phy.c
> +++ b/drivers/net/phy/phy.c
> @@ -1,4 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0+
> + err = phy_read_status(phydev);
> + if (err)
> + return err;

This seems to be completely wrong at that place.

> /* Framework for configuring and reading PHY devices
> * Based on code in sungem_phy.c and gianfar_phy.c
> *
> @@ -525,6 +528,11 @@ static int phy_check_link_status(struct phy_device *phydev)
>
> WARN_ON(!mutex_is_locked(&phydev->lock));
>
> + /* Do a fake read */
> + err = phy_read(phydev, MII_BMSR);
> + if (err < 0)
> + return err;
> +
> err = phy_read_status(phydev);
> if (err)
> return err;
>

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