Re: [PATCH net-next 08/30] net: dsa: mt7530: change p{5,6}_interface to p{5,6}_configured

Arınç ÜNAL
2023-06-10T10:58:51Z

On 4.06.2023 19:14, Arınç ÜNAL wrote:
> On 4.06.2023 19:06, Russell King (Oracle) wrote:
>> On Sun, Jun 04, 2023 at 05:00:11PM +0100, Russell King (Oracle) wrote:
>>> On Sun, Jun 04, 2023 at 04:13:39PM +0100, Russell King (Oracle) wrote:
>>>> On Sun, Jun 04, 2023 at 04:14:31PM +0300, Arınç ÜNAL wrote:
>>>>> On 4.06.2023 16:07, Russell King (Oracle) wrote:
>>>>>> On Sun, Jun 04, 2023 at 03:55:17PM +0300, Vladimir Oltean wrote:
>>>>>>> On Sun, Jun 04, 2023 at 01:18:04PM +0100, Russell King (Oracle)
>>>>>>> wrote:
>>>>>>>> I don't remember whether Vladimir's firmware validator will fail
>>>>>>>> for
>>>>>>>> mt753x if CPU ports are not fully described, but that would be well
>>>>>>>> worth checking. If it does, then we can be confident that phylink
>>>>>>>> will always be used, and those bypassing calls should not be
>>>>>>>> necessary.
>>>>>>>
>>>>>>> It does, I've just retested this:
>>>>>>>
>>>>>>> [    8.469152] mscc_felix 0000:00:00.5: OF node
>>>>>>> /soc/pcie@1f0000000/ethernet-switch@0,5/ports/port@4 of CPU port
>>>>>>> 4 lacks the required "phy-handle", "fixed-link" or "managed"
>>>>>>> properties
>>>>>>> [    8.494571] mscc_felix 0000:00:00.5: error -EINVAL: Failed to
>>>>>>> register DSA switch
>>>>>>> [    8.502151] mscc_felix: probe of 0000:00:00.5 failed with
>>>>>>> error -22
>>>>>>
>>>>>> ... which isn't listed in dsa_switches_apply_workarounds[], and
>>>>>> neither is mt753x. Thanks.
>>>>>>
>>>>>> So, that should be sufficient to know that the CPU port will always
>>>>>> properly described, and thus bypassing phylink in mt753x for the CPU
>>>>>> port should not be necessary.
>>>>>
>>>>> Perfect! If I understand correctly, there's this code - specific to
>>>>> MT7531
>>>>> and MT7988 ports being used as CPU ports - which runs in addition
>>>>> to what's
>>>>> in mt753x_phylink_mac_config():
>>>>>
>>>>>     mt7530_write(priv, MT7530_PMCR_P(port),
>>>>>              PMCR_CPU_PORT_SETTING(priv->id));
>>>>>
>>>>> This should be put on mt753x_phylink_mac_config(), under priv->id ==
>>>>> ID_MT7531, priv->id == ID_MT7988, and dsa_is_cpu_port(ds, port)
>>>>> checks?
>>>>
>>>> Please remember that I have very little knowledge of MT753x, so in
>>>> order to answer this question, I've read through the mt7530 driver
>>>> code.
>>>>
>>>> Looking at mt7530.h:
>>>>
>>>> #define  PMCR_CPU_PORT_SETTING(id)      (PMCR_FORCE_MODE_ID((id)) | \
>>>>                                           PMCR_IFG_XMIT(1) |
>>>> PMCR_MAC_MODE | \
>>>>                                           PMCR_BACKOFF_EN |
>>>> PMCR_BACKPR_EN | \
>>>>                                           PMCR_TX_EN | PMCR_RX_EN | \
>>>>                                           PMCR_TX_FC_EN |
>>>> PMCR_RX_FC_EN | \
>>>>                                           PMCR_FORCE_SPEED_1000 | \
>>>>                                           PMCR_FORCE_FDX |
>>>> PMCR_FORCE_LNK)
>>>>
>>>> This seems to be some kind of port control register that sets amongst
>>>> other things parameters such as whether flow control is enabled, the
>>>> port speed, the duplex setting, whether link is forced up, etc.
>>>>
>>>> Looking at what mt753x_phylink_mac_link_up() does:
>>>>
>>>> 1. it sets PMCR_RX_EN | PMCR_TX_EN | PMCR_FORCE_LNK.
>>>> 2. it sets PMCR_FORCE_SPEED_1000 if speed was 1000Mbps, or if using
>>>>     an internal, TRGMII, 1000base-X or 2500base-X phy interface mode.
>>>> 3. it sets PMCR_FORCE_FDX if full duplex was requested.
>>>> 4. it sets PMCR_TX_FC_EN if full duplex was requested with tx pause.
>>>> 5. it sets PMCR_RX_FC_EN if full duplex was requested with rx pause.
>>>>
>>>> So, provided this is called with the appropriate parameters, for a
>>>> fixed link, that will leave the following:
>>>>
>>>>     PMCR_FORCE_MODE_ID(id)
>>>>     PMCR_IFG_XMIT(1)
>>>>     PMCR_MAC_MODE
>>>>     PMCR_BACKOFF_EN
>>>>     PMCR_BACKPR_EN
>>>>
>>>> If we now look at mt753x_phylink_mac_config(), this sets
>>>> PMCR_IFG_XMIT(1), PMCR_MAC_MODE, PMCR_BACKOFF_EN, PMCR_BACKPR_EN,
>>>> and PMCR_FORCE_MODE_ID(priv->id), which I believe is everything that
>>>> PMCR_CPU_PORT_SETTING(priv->id) is doing.
>>>>
>>>> So, Wouldn't a fixed-link description indicating 1Gbps, full duplex
>>>> with pause cause phylink to call both mt753x_phylink_mac_config() and
>>>> mt753x_phylink_mac_link_up() with appropriate arguments to set all
>>>> of these parameters in PMCR?
>>>>
>>>> Now, I'm going to analyse something else. mt7531_cpu_port_config()
>>>> is called from mt753x_cpu_port_enable(), which is itself called from
>>>> mt7531_setup_common(). That is ultimately called from the DSA switch
>>>> ops .setup() method.
>>>>
>>>> This method is called from dsa_switch_setup() for each switch in the
>>>> DSA tree. dsa_tree_setup_switches() calls this, and is called from
>>>> dsa_tree_setup().  Once dsa_tree_setup_switches() finishes
>>>> successfully, dsa_tree_setup_ports() will be called. This will then
>>>> setup DSA and CPU ports, which will then setup a phylink instance
>>>> for these ports. phylink will parse the firmware description for
>>>> the port. DSA will then call dsa_port_enable().
>>>>
>>>> dsa_port_enable() will then call any port_enable() method in the
>>>> mt7530.c driver, which will be mt7530_port_enable(). This then...
>>>>
>>>>          mt7530_clear(priv, MT7530_PMCR_P(port),
>>>> PMCR_LINK_SETTINGS_MASK);
>>>>
>>>> which is:
>>>>
>>>> #define  PMCR_LINK_SETTINGS_MASK        (PMCR_TX_EN |
>>>> PMCR_FORCE_SPEED_1000 | \
>>>>                                           PMCR_RX_EN |
>>>> PMCR_FORCE_SPEED_100 | \
>>>>                                           PMCR_TX_FC_EN |
>>>> PMCR_RX_FC_EN | \
>>>>                                           PMCR_FORCE_FDX |
>>>> PMCR_FORCE_LNK | \
>>>>                                           PMCR_FORCE_EEE1G |
>>>> PMCR_FORCE_EEE100)
>>>>
>>>> So it wipes out all the PMCR settings that mt7531_cpu_port_config()
>>>> performed - undoing *everything* below that switch() statement in
>>>> mt7531_cpu_port_config()!
>>>>
>>>> Once the port_enable() method returns, DSA will then call
>>>> phylink_start(), which will trigger phylink to bring up the link
>>>> according to the settings it has, which will mean phylink calls
>>>> the mac_config(), pcs_config(), pcs_link_up() and mac_link_up()
>>>> with the appropriate parameters for the firmware described link.
>>>>
>>>> So I think I have the answer to my initial thought: do the calls in
>>>> mt7531_cpu_port_config() to the phylink methods have any use what so
>>>> ever? The answer is no, they are entirely useless. The same goes for
>>>> the other cpu_port_config() methods that do something similar. The
>>>> same goes for the PMCR register write that's changing any bits
>>>> included in PMCR_LINK_SETTINGS_MASK.
>>>>
>>>> What that means is that mt7988_cpu_port_config() can be entirely
>>>> removed, it serves no useful purpose what so ever. For
>>>> mt7531_cpu_port_config(), it only needs to set priv->p[56]_interface
>>>> which, as far as I can see, probably only avoids mac_config() doing
>>>> any pad setup (that's a guess.)
>>>>
>>>> At least that's what I gather from reading through the driver and
>>>> DSA code. It may be I've missed something, but currently, I think
>>>> that these cpu_port_config() functions aren't doing too much that
>>>> is actually useful work.
>>>
>>> Essentially, I think this change will have no effect at all on the
>>> driver, because any effect this code has is totally undone when the
>>> driver's port_enable() method is called:
>>>
>>> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
>>> index 9bc54e1348cb..447e63d74e0c 100644
>>> --- a/drivers/net/dsa/mt7530.c
>>> +++ b/drivers/net/dsa/mt7530.c
>>> @@ -2859,8 +2859,6 @@ mt7531_cpu_port_config(struct dsa_switch *ds,
>>> int port)
>>>   {
>>>       struct mt7530_priv *priv = ds->priv;
>>>       phy_interface_t interface;
>>> -    int speed;
>>> -    int ret;
>>>       switch (port) {
>>>       case 5:
>>> @@ -2880,36 +2878,6 @@ mt7531_cpu_port_config(struct dsa_switch *ds,
>>> int port)
>>>           return -EINVAL;
>>>       }
>>> -    if (interface == PHY_INTERFACE_MODE_2500BASEX)
>>> -        speed = SPEED_2500;
>>> -    else
>>> -        speed = SPEED_1000;
>>> -
>>> -    ret = mt7531_mac_config(ds, port, MLO_AN_FIXED, interface);
>>> -    if (ret)
>>> -        return ret;
>>> -    mt7530_write(priv, MT7530_PMCR_P(port),
>>> -             PMCR_CPU_PORT_SETTING(priv->id));
>>> -    mt753x_phylink_pcs_link_up(&priv->pcs[port].pcs, MLO_AN_FIXED,
>>> -                   interface, speed, DUPLEX_FULL);
>>> -    mt753x_phylink_mac_link_up(ds, port, MLO_AN_FIXED, interface, NULL,
>>> -                   speed, DUPLEX_FULL, true, true);
>>> -
>>> -    return 0;
>>> -}
>>> -
>>> -static int
>>> -mt7988_cpu_port_config(struct dsa_switch *ds, int port)
>>> -{
>>> -    struct mt7530_priv *priv = ds->priv;
>>> -
>>> -    mt7530_write(priv, MT7530_PMCR_P(port),
>>> -             PMCR_CPU_PORT_SETTING(priv->id));
>>> -
>>> -    mt753x_phylink_mac_link_up(ds, port, MLO_AN_FIXED,
>>> -                   PHY_INTERFACE_MODE_INTERNAL, NULL,
>>> -                   SPEED_10000, DUPLEX_FULL, true, true);
>>> -
>>>       return 0;
>>>   }
>>> @@ -3165,7 +3133,6 @@ const struct mt753x_info mt753x_table[] = {
>>>           .phy_read_c45 = mt7531_ind_c45_phy_read,
>>>           .phy_write_c45 = mt7531_ind_c45_phy_write,
>>>           .pad_setup = mt7988_pad_setup,
>>> -        .cpu_port_config = mt7988_cpu_port_config,
>>>           .mac_port_get_caps = mt7988_mac_port_get_caps,
>>>           .mac_port_config = mt7988_mac_config,
>>>       },
>>
>> ... and with that patch we can remove the definition of
>> PMCR_CPU_PORT_SETTING() as well!
>>
>> There is one possibility why we may not be able to remove this code -
>> whether there's something in this which requires the CPU port to be
>> setup prior to something else. Only someone knowledgeable of the
>> hardware, or who has the hardware in front and can test would be able
>> to work that out.
>
> I am on the same page with your explanation so far. I will test this out
> on MT7531. Thanks a lot for looking at this!

I was able to confirm all user ports of the MT7531BE switch
transmit/receive traffic to/from the SGMII CPU port and computer fine
after getting rid of priv->info->cpu_port_config().

Tried all user ports being affine to the RGMII CPU port, that works too.

https://github.com/arinc9/linux/commit/4e79313a95d45950cab526456ef0030286ba4d4e

Arınç