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

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Message-ID: <372a45c3-1372-4956-8d42-8e989f86d131@microchip.com>
Date: Mon, 18 Mar 2024 11:01:12 +0000
From: <Parthiban.Veerasooran@...rochip.com>
To: <andrew@...n.ch>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <horms@...nel.org>, <saeedm@...dia.com>,
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	<Selvamani.Rajagopal@...emi.com>, <Nicolas.Ferre@...rochip.com>,
	<benjamin.bigler@...nformulastudent.ch>
Subject: Re: [PATCH net-next v3 06/12] net: ethernet: oa_tc6: implement
 internal PHY initialization

Hi Andrew,

On 08/03/24 7:03 pm, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
>> 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.
> 
> Yes, please add it to mdio.h
Sure will add it in the mdio.h file.
> 
>> /* 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;
> 
> I would probably use a switch statement.
Ah ok, I will use switch here.
> 
>>
>>           else
>>
>>                   return -ENOTSUPP;
> 
> 802.3 says:
> 
>    If a device supports the MDIO interface it shall respond to all
>    possible register addresses for the device and return a value of
>    zero for undefined and unsupported registers. Writes to undefined
>    registers and read-only registers shall have no effect. The
>    operation of an MMD shall not be affected by writes to reserved and
>    unsupported register bits, and such register bits shall return a
>    value of zero when read.
> 
> So maybe return 0. ENOTSUPP is wrong, that is an NFS only error
> code. The generic one is EOPNOTSUPP. I would say -EOPNOTSUPP is also
> O.K.
Sure, I will use -EOPNOTSUPP in the next version instead of -ENOTSUPP.
> 
>>           ret = oa_tc6_read_register(tc6, (mms << 16) | regnum, &regval);
>>
>>           if (ret)
>>
>>                   return -ENODEV;
> 
> oa_tc6_read_register() should return an error code, so return whatever
> is returns. Don't overwrite error codes. It makes it harder to track
> errors through the call stack.
Ah ok, will return the error code from oa_tc6_read_register() in the 
next version.

Best regards,
Parthiban V
> 
>         Andrew
>