Re: [PATCH net] amd-xgbe: read link status twice to avoid inconsistencies

[Rangoju, Raju]

On 5/15/2025 5:37 AM, Andrew Lunn wrote:
> On Thu, May 15, 2025 at 01:11:45AM +0530, Raju Rangoju wrote:
> > The link status is latched low, so read the register twice to get the
> > current status and avoid link inconsistencies.
> >
> > As per IEEE 802.3 "Table 22-8 - Status register bit definitions"
> > 1.2  Link Status  1 = link is up    0 = link is down    RO/LL
> >
> > Fixes: 4f3b20bfbb75 ("amd-xgbe: add support for rx-adaptation")
> > Signed-off-by: Raju Rangoju <Raju.Rangoju@xxxxxxx>
> > ---
> >   drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> > index 268399dfcf22..d233e3faa1a9 100644
> > --- a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> > +++ b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> > @@ -2914,6 +2914,10 @@ static int xgbe_phy_link_status(struct xgbe_prv_data *pdata, int *an_restart)
> >   		}
> >   
> >   		/* check again for the link and adaptation status */
> > +		/* Link status is latched low, so read once to clear
> > +		 * and then read again to get current state
> > +		 */
> > +		reg = XMDIO_READ(pdata, MDIO_MMD_PCS, MDIO_STAT1);
>
>
> Since this is not a phylib user, i don't care too much, but:
>
> https://elixir.bootlin.com/linux/v6.14.6/source/drivers/net/phy/phy_device.c#L2514
>
> 	/* The link state is latched low so that momentary link
> 	 * drops can be detected. Do not double-read the status
> 	 * in polling mode to detect such short link drops except
> 	 * the link was already down.
> 	 */
>
> So you don't care about short link drops? You don't want to tell user
> space the link went away and came back? It never happened.

Thanks Andrew for point this out. I'll re-spin v2 addressing these.

> 	Andrew