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Date:   Fri, 10 May 2019 09:32:24 +0200
From:   Michael Grzeschik <mgr@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Tristram.Ha@...rochip.com, kernel@...gutronix.de,
        UNGLinuxDriver@...rochip.com, netdev@...r.kernel.org
Subject: Re: [RFC 1/3] mdio-bitbang: add SMI0 mode support

On Thu, May 09, 2019 at 04:29:25PM +0200, Andrew Lunn wrote:
> On Wed, May 08, 2019 at 11:13:28PM +0200, Michael Grzeschik wrote:
> > Some microchip phys support the Serial Management Interface Protocol
> > (SMI) for the configuration of the extended register set. We add
> > MII_ADDR_SMI0 as an availabe interface to the mdiobb write and read
> > functions, as this interface can be easy realized using the bitbang mdio
> > driver.
> > 
> > Signed-off-by: Sam Ravnborg <sam@...nborg.org>
> > Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> > ---
> >  drivers/net/phy/mdio-bitbang.c | 10 ++++++++++
> >  include/linux/phy.h            | 12 ++++++++++++
> >  2 files changed, 22 insertions(+)
> > 
> > diff --git a/drivers/net/phy/mdio-bitbang.c b/drivers/net/phy/mdio-bitbang.c
> > index 5136275c8e739..a978f8a9a172b 100644
> > --- a/drivers/net/phy/mdio-bitbang.c
> > +++ b/drivers/net/phy/mdio-bitbang.c
> > @@ -22,6 +22,10 @@
> >  #define MDIO_READ 2
> >  #define MDIO_WRITE 1
> >  
> > +#define SMI0_RW_OPCODE	0
> > +#define SMI0_READ_PHY	(1 << 4)
> > +#define SMI0_WRITE_PHY	(0 << 4)
> > +
> >  #define MDIO_C45 (1<<15)
> >  #define MDIO_C45_ADDR (MDIO_C45 | 0)
> >  #define MDIO_C45_READ (MDIO_C45 | 3)
> > @@ -157,6 +161,9 @@ static int mdiobb_read(struct mii_bus *bus, int phy, int reg)
> >  	if (reg & MII_ADDR_C45) {
> >  		reg = mdiobb_cmd_addr(ctrl, phy, reg);
> >  		mdiobb_cmd(ctrl, MDIO_C45_READ, phy, reg);
> > +	} else if (reg & MII_ADDR_SMI0) {
> > +		mdiobb_cmd(ctrl, SMI0_RW_OPCODE,
> > +			   (reg & 0xE0) >> 5 | SMI0_READ_PHY, reg);
> >  	} else
> >  		mdiobb_cmd(ctrl, MDIO_READ, phy, reg);
> >  
> > @@ -188,6 +195,9 @@ static int mdiobb_write(struct mii_bus *bus, int phy, int reg, u16 val)
> >  	if (reg & MII_ADDR_C45) {
> >  		reg = mdiobb_cmd_addr(ctrl, phy, reg);
> >  		mdiobb_cmd(ctrl, MDIO_C45_WRITE, phy, reg);
> > +	} else if (reg & MII_ADDR_SMI0) {
> > +		mdiobb_cmd(ctrl, SMI0_RW_OPCODE,
> > +			   (reg & 0xE0) >> 5 | SMI0_WRITE_PHY, reg);
> >  	} else
> >  		mdiobb_cmd(ctrl, MDIO_WRITE, phy, reg);
> >  
> > diff --git a/include/linux/phy.h b/include/linux/phy.h
> > index 073fb151b5a99..f011722fbd5c2 100644
> > --- a/include/linux/phy.h
> > +++ b/include/linux/phy.h
> > @@ -199,6 +199,18 @@ static inline const char *phy_modes(phy_interface_t interface)
> >     IEEE 802.3ae clause 45 addressing mode used by 10GIGE phy chips. */
> >  #define MII_ADDR_C45 (1<<30)
> >  
> > +/* Serial Management Interface (SMI) uses the following frame format:
> > + *
> > + *       preamble|start|Read/Write|  PHY   |  REG  |TA|   Data bits      | Idle
> > + *               |frame| OP code  |address |address|  |                  |
> > + * read | 32x1´s | 01  |    00    | 1xRRR  | RRRRR |Z0| 00000000DDDDDDDD |  Z
> > + * write| 32x1´s | 01  |    00    | 0xRRR  | RRRRR |10| xxxxxxxxDDDDDDDD |  Z
> > + *
> > + * The register number is encoded with the 5 least significant bits in REG
> > + * and the 3 most significant bits in PHY
> > + */
> > +#define MII_ADDR_SMI0 (1<<31)
> > +
> 
> Michael
> 
> This is a Micrel Proprietary protocol. So we should reflect this in
> the name. MII_ADDR_MICREL_SMI? Why the 0? Are there different
> versions? Maybe replace all SMI0 with MICREL_SMI in mdio-bitbang.c

There are two variants of the SMI interface.

The KSZ8863/73/93 Products use the above Variant described as "SMI0".

The KSZ8864/95 Products use another layout:

      preamble|start|Read/Write|  PHY   |  REG  |TA|   Data bits      | Idle
              |frame| OP code  |address |address|  |                  |
read | 32x1´s | 01  |    10    | RR11R  | RRRRR |Z0| 00000000DDDDDDDD |  Z
write| 32x1´s | 01  |    01    | RR11R  | RRRRR |10| xxxxxxxxDDDDDDDD |  Z

So they describe their write/read operation in the OP code rather then
the PHY address.

We could change the SMI index to SMI_KSZ88X3 for the current SMI0 to
give it a more descriptive name. Beside we never know if Microchip
will add the same protocol to other numbered switches. What naming
would you prefer?

> When i look at this, i don't see how a normal MDIO bus driver is going
> to support this. Only the bit banging driver, or maybe a Micrel MDIO
> bus master hardware driver. So i think the diagram should be placed
> into mdio-bitbang.c, and it would be nice to add a diagram of standard
> SMI.

Right. I will move the description to mdio-bitbang.c.

Thanks,
Michael

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