netdev - Re: [PATCH 2/3] net: socionext: Add dummy PHY register read in phy

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Date:   Thu, 18 Oct 2018 20:01:21 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     masahisa.kojima@...aro.org, netdev@...r.kernel.org
Cc:     ilias.apalodimas@...aro.org, jaswinder.singh@...aro.org,
        ard.biesheuvel@...aro.org, osaki.yoshitoyo@...ionext.com
Subject: Re: [PATCH 2/3] net: socionext: Add dummy PHY register read in
 phy_write()



On 10/18/2018 6:08 PM, masahisa.kojima@...aro.org wrote:
> From: Masahisa Kojima <masahisa.kojima@...aro.org>
> 
> There is a compatibility issue between RTL8211E implemented
> in Developerbox and netsec network controller IP(F_GMAC4).
> 
> RTL8211E expects MDC clock must be kept toggling for several
> clock cycle with MDIO high before entering the IDLE state.
> To meet this requirement, netsec driver needs to issue dummy
> read(e.g. read PHYID1(offset 0x2) register) right after write.
> 
> Signed-off-by: Masahisa Kojima <masahisa.kojima@...aro.org>
> Signed-off-by: Yoshitoyo Osaki <osaki.yoshitoyo@...ionext.com>
> ---
>  drivers/net/ethernet/socionext/netsec.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
> index 273cc5fc07e0..e7faaf8be99e 100644
> --- a/drivers/net/ethernet/socionext/netsec.c
> +++ b/drivers/net/ethernet/socionext/netsec.c
> @@ -431,9 +431,12 @@ static int netsec_mac_update_to_phy_state(struct netsec_priv *priv)
>  	return 0;
>  }
>  
> +static int netsec_phy_read(struct mii_bus *bus, int phy_addr, int reg_addr);
> +
>  static int netsec_phy_write(struct mii_bus *bus,
>  			    int phy_addr, int reg, u16 val)
>  {
> +	int status;
>  	struct netsec_priv *priv = bus->priv;
>  
>  	if (netsec_mac_write(priv, GMAC_REG_GDR, val))
> @@ -446,8 +449,19 @@ static int netsec_phy_write(struct mii_bus *bus,
>  			      GMAC_REG_SHIFT_CR_GAR)))
>  		return -ETIMEDOUT;
>  
> -	return netsec_mac_wait_while_busy(priv, GMAC_REG_GAR,
> -					  NETSEC_GMAC_GAR_REG_GB);
> +	status = netsec_mac_wait_while_busy(priv, GMAC_REG_GAR,
> +					    NETSEC_GMAC_GAR_REG_GB);
> +
> +	/* Developerbox implements RTL8211E PHY and there is
> +	 * a compatibility problem with F_GMAC4.
> +	 * RTL8211E expects MDC clock must be kept toggling for several
> +	 * clock cycle with MDIO high before entering the IDLE state.
> +	 * To meet this requirement, netsec driver needs to issue dummy
> +	 * read(e.g. read PHYID1(offset 0x2) register) right after write.
> +	 */
> +	netsec_phy_read(bus, phy_addr, 2);

MII_PHYSID1 instead of 0x2 would be preferable. It is not clear to me
from your commit message if this is a problem specific to your MDIO
controller implementation and the RTL8211E PHY or if this is a general
problem of the PHY irrespective of the MDIO controller it is interface
with. If the latter, then we should seek a solution at a different layer
such that other systems don't have that same problem.

Thank you!
-- 
Florian