netdev - RE: [PATCH net-next v4 2/2] phy: mscc: Add support for RGMII delay configuration

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Date: Wed, 24 May 2023 11:38:15 +0000
From: "Katakam, Harini" <harini.katakam@....com>
To: Vladimir Oltean <vladimir.oltean@....com>
CC: "andrew@...n.ch" <andrew@...n.ch>, "hkallweit1@...il.com"
	<hkallweit1@...il.com>, "linux@...linux.org.uk" <linux@...linux.org.uk>,
	"davem@...emloft.net" <davem@...emloft.net>, "kuba@...nel.org"
	<kuba@...nel.org>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"pabeni@...hat.com" <pabeni@...hat.com>, "wsa+renesas@...g-engineering.com"
	<wsa+renesas@...g-engineering.com>, "simon.horman@...igine.com"
	<simon.horman@...igine.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "harinikatakamlinux@...il.com"
	<harinikatakamlinux@...il.com>, "Simek, Michal" <michal.simek@....com>,
	"Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
Subject: RE: [PATCH net-next v4 2/2] phy: mscc: Add support for RGMII delay
 configuration

Hi Vladimir,

> -----Original Message-----
> From: Vladimir Oltean <vladimir.oltean@....com>
> Sent: Wednesday, May 24, 2023 3:39 PM
> To: Katakam, Harini <harini.katakam@....com>
> Cc: andrew@...n.ch; hkallweit1@...il.com; linux@...linux.org.uk;
> davem@...emloft.net; kuba@...nel.org; edumazet@...gle.com;
> pabeni@...hat.com; wsa+renesas@...g-engineering.com;
> simon.horman@...igine.com; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; harinikatakamlinux@...il.com; Simek, Michal
> <michal.simek@....com>; Pandey, Radhey Shyam
> <radhey.shyam.pandey@....com>
> Subject: Re: [PATCH net-next v4 2/2] phy: mscc: Add support for RGMII delay
> configuration
> 
> On Mon, May 22, 2023 at 05:58:29PM +0530, Harini Katakam wrote:
> > diff --git a/drivers/net/phy/mscc/mscc_main.c
> b/drivers/net/phy/mscc/mscc_main.c
> > index 91010524e03d..9e856231e464 100644
> > --- a/drivers/net/phy/mscc/mscc_main.c
> > +++ b/drivers/net/phy/mscc/mscc_main.c
> > @@ -525,17 +525,14 @@ static int vsc85xx_rgmii_set_skews(struct
> phy_device *phydev, u32 rgmii_cntl,
> >  {
> >  	u16 rgmii_rx_delay_pos = ffs(rgmii_rx_delay_mask) - 1;
> >  	u16 rgmii_tx_delay_pos = ffs(rgmii_tx_delay_mask) - 1;
> > +	struct vsc8531_private *vsc8531 = phydev->priv;
> >  	u16 reg_val = 0;
> >  	int rc;
> >
> >  	mutex_lock(&phydev->lock);
> >
> > -	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID ||
> > -	    phydev->interface == PHY_INTERFACE_MODE_RGMII_ID)
> > -		reg_val |= RGMII_CLK_DELAY_2_0_NS << rgmii_rx_delay_pos;
> > -	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID ||
> > -	    phydev->interface == PHY_INTERFACE_MODE_RGMII_ID)
> > -		reg_val |= RGMII_CLK_DELAY_2_0_NS << rgmii_tx_delay_pos;
> > +	reg_val |= vsc8531->rx_delay << rgmii_rx_delay_pos;
> > +	reg_val |= vsc8531->tx_delay << rgmii_tx_delay_pos;
> 
> What about vsc8584_config_init() -> vsc85xx_rgmii_set_skews()? Who will
> have configured rx_delay and tx_delay for that call path?

In my current series "rx_delay" and "tx_delay" would end up 0 and a
delay of 0.2 ns will be programmed (default for that field).
I guess if the phy-mode is RGMII/-ID on VSC8584, 2ns will not be programmed.
This will be a problem for any device not using vsc85xx_config_init

> 
> Isn't it better to absorb the device tree parsing logic into
> vsc85xx_rgmii_set_skews(), I wonder?

Yes, that is possible, let me respin. That will ensure existing values are not broken
for any VSC85xx user, if they do not have delay properties in the DT.

> 
> And if we do that, is it still necessary to use struct vsc8531_private
> as temporary storage space from vsc85xx_config_init() to
> vsc85xx_rgmii_set_skews(),
> or will two local variables (rx_delay, tx_delay) serve that purpose just fine?

No need of the structure member, local variables will do.

> 
> >
> >  	rc = phy_modify_paged(phydev, MSCC_PHY_PAGE_EXTENDED_2,
> >  			      rgmii_cntl,
> > @@ -1808,10 +1805,34 @@ static irqreturn_t
> vsc8584_handle_interrupt(struct phy_device *phydev)
> >  	return IRQ_HANDLED;
> >  }
> >
> > +static const int vsc8531_internal_delay[] = {200, 800, 1100, 1700, 2000,
> 2300,
> > +					     2600, 3400};
> 
> Could you please avoid intermingling this with the function code, and
> move it at the top of mscc_main.c?
> 
> Also, vsc8531_internal_delay[] or vsc85xx_internal_delay[]? The values
> are also good for VSC8572, the other caller of vsc85xx_rgmii_set_skews().

vsc85xx_internal_delay is more appropriate, will change.

Thanks for the review.

Regards,
Harini