Re: [PATCH net-next v3 06/12] net: ethernet: oa_tc6: implement internal PHY initialization

[<Parthiban.Veerasooran@microchip.com>]

Hi Andrew,

On 07/03/24 10:06 pm, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
>>>> +static int oa_tc6_mdiobus_register(struct oa_tc6 *tc6)
>>>> +{
>>>> +     int ret;
>>>> +
>>>> +     tc6->mdiobus = mdiobus_alloc();
>>>> +     if (!tc6->mdiobus) {
>>>> +             netdev_err(tc6->netdev, "MDIO bus alloc failed\n");
>>>> +             return -ENODEV;
>>>> +     }
>>>> +
>>>> +     tc6->mdiobus->priv = tc6;
>>>> +     tc6->mdiobus->read = oa_tc6_mdiobus_direct_read;
>>>> +     tc6->mdiobus->write = oa_tc6_mdiobus_direct_write;
>>>
>>> This might get answered in later patches. PLCA registers are in C45
>>> address space, VEND1 if i remember correctly. You don't provide any
>>> C45 access methods here. Does TC6 specify that C45 over C22 must be
>>> implemented?
>> No the spec doesn't say anything like this. But, as C22 registers are
>> mapped in the MMS 0, registers 0xD and 0xE can be used to access C45
>> registers indirectly. That's why the driver implemented the above
>> functions. I agree that indirect access is slower and requires more
>> control commands than direct access. So implementing the direct access
>> of C45 registers will overcome this issue.
> 
> It is not just about performance. It is about compliance to the
> standard. The standard does not say anything about C45 over C22. So
> there is no reason to expect a PHY device to implement it. It might,
> but its optional.
Yes, understood.
> 
>>> The standard does say:
>>>
>>> Vendor specific registers may be mapped into MMS 10 though MMS
>>> 15. When directly mapped, PHY vendor specific registers in MMD 30 or
>>> MMD 31 would be mapped into the vendor specific MMS 10 through MMS 15.
>>>
>>> So i'm thinking you might need to provide C45 access, at least MMD 30,
>>> via MMS 10-15?
>> Thanks for this detailed comment. If understand you correctly by
>> consolidating all your above explanations, the driver should provide C45
>> access to the PHY vendor specific and PLCA registers (MMD 31). As per
>> the specification, Table 6 describes the Register Memory Map Selector
>> (MMS) Assignment. In this, MMS 4 maps the PHY vendor specific and PLCA
>> registers. They are in the MMD 31 address space as per spec. They can be
>> directly accessed using read_c45 and write_c45 functions in the mdio bus.
> 
> Yes. I think this is required to conform to the standard.
Ok then let's implement like below.
> 
>> In Microchip's MAC-PHY (LAN8650), PHY – Vendor Specific and PLCA
>> Registers (MMD 31) mapped in the MMS 4 as per the table 6 in the spec.
>> There is no other PHY vendor specific registers are mapped in the MMS 10
>> through 15. No idea whether any other vendor's MAC-PHY uses MMS 10
>> through 15 to map PHY – Vendor Specific and PLCA Registers (MMD 31).
>>
>> I have given the code below for the C45 access methods. Kindly check is
>> this something you expected?
> 
> The code got mangled by your mail client :-(
Oh sorry.
> 
>> --- Code starts ---
>>
>> /* PHY – Vendor Specific and PLCA Registers (MMD 31) */
>>
>> #define OA_TC6_PHY_VS_PLCA_REG_ADDR_BASE        0x40000
>> ,,,
>>
>> static int oa_tc6_mdiobus_read_c45(struct mii_bus *bus, int addr, int
>> devnum, int regnum)
>> {
>>
>>           struct oa_tc6 *tc6 = bus->priv;
>>
>>           u32 regval;
>>
>>           bool ret;
>>
>>
>>
>>           ret = oa_tc6_read_register(tc6,
>> OA_TC6_PHY_VS_PLCA_REG_ADDR_BASE | regnum, &regval);
> 
> You appear to ignore devnum. I don't think you can do that. The core
> phylib code might try to access other MMDs, e.g. it might try to see
> if EEE is supported, by reading MDIO_MMD_PCS, MDIO_PCS_EEE_ABLE.
Ok, as per the table 6 in the spec, PHY C45 registers are mapped in the 
MMS like below,

PHY – PCS Registers (MMD 3)  --->  MMS 2
PHY – PMA/PMD Registers (MMD 1)  --->   MMS 3
PHY – Vendor Specific and PLCA Registers (MMD 31)  --->  MMS 4
PHY – Auto-Negotiation Registers (MMD 7)  --->  MMS 5
PHY – Power Unit (MMD 13)  --->  MMS 6

MMD 13 for PHY - Power Unit is not defined in the mdio.h. So in the 
below code I have defined it locally (MDIO_MMD_POWER_UNIT). May be 
needed to do this in the mdio.h file when coming to this patch.

https://elixir.bootlin.com/linux/v6.8-rc7/source/include/uapi/linux/mdio.h

Hope you are expecting like below? I believe this time the code will not 
get mangled. If happens then sorry for that.

--- Code starts here ---

/* PHY – Clause 45 registers memory map selector (MMS) as per table 6 in 
the OPEN Alliance specification.
  */
#define OA_TC6_PHY_PCS_MMS2                     2       /* MMD 3 */
#define OA_TC6_PHY_PMA_PMD_MMS3                 3       /* MMD 1 */
#define OA_TC6_PHY_VS_PLCA_MMS4                 4       /* MMD 31 */
#define OA_TC6_PHY_AUTO_NEG_MMS5                5       /* MMD 7 */
#define OA_TC6_PHY_POWER_UNIT_MMS6              6       /* MMD 13 */

/* MDIO Manageable Device (MMD) for PHY Power Unit */
#define MDIO_MMD_POWER_UNIT                     13      /* PHY Power Unit */

static int oa_tc6_mdiobus_read_c45(struct mii_bus *bus, int addr, int 
devnum, int regnum)
{ 

         struct oa_tc6 *tc6 = bus->priv; 

         u32 regval; 

         bool ret; 

         u32 mms; 

 

         if (devnum == MDIO_MMD_PCS) 

                 mms = OA_TC6_PHY_PCS_MMS2; 

         else if (devnum == MDIO_MMD_PMAPMD) 

                 mms = OA_TC6_PHY_PMA_PMD_MMS3; 

         else if (devnum == MDIO_MMD_VEND2) 

                 mms = OA_TC6_PHY_VS_PLCA_MMS4; 

         else if (devnum == MDIO_MMD_AN) 

                 mms = OA_TC6_PHY_AUTO_NEG_MMS5; 

         else if (devnum == MDIO_MMD_POWER_UNIT) 

                 mms = OA_TC6_PHY_POWER_UNIT_MMS6; 

         else 

                 return -ENOTSUPP; 

 

         ret = oa_tc6_read_register(tc6, (mms << 16) | regnum, &regval); 

         if (ret) 

                 return -ENODEV; 

 

         return regval; 

} 


static int oa_tc6_mdiobus_write_c45(struct mii_bus *bus, int addr, int 
devnum, int regnum, u16 val)
{ 

         struct oa_tc6 *tc6 = bus->priv; 

         u32 mms; 

 

         if (devnum == MDIO_MMD_PCS) 

                 mms = OA_TC6_PHY_PCS_MMS2; 

         else if (devnum == MDIO_MMD_PMAPMD) 

                 mms = OA_TC6_PHY_PMA_PMD_MMS3; 

         else if (devnum == MDIO_MMD_VEND2) 

                 mms = OA_TC6_PHY_VS_PLCA_MMS4; 

         else if (devnum == MDIO_MMD_AN) 

                 mms = OA_TC6_PHY_AUTO_NEG_MMS5; 

         else if (devnum == MDIO_MMD_POWER_UNIT) 

                 mms = OA_TC6_PHY_POWER_UNIT_MMS6; 

         else 

                 return -ENOTSUPP; 

 

         return oa_tc6_write_register(tc6, (mms << 16) | regnum, val); 

} 


--- Code ends here ---

Best regards,
Parthiban V
> 
>          Andrew
>