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

["Arınç ÜNAL" <arinc.unal@arinc9.com>]

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!

Arınç