Message-ID: <24ce3ff9-22b3-4d5d-ade4-3b8521aeadfe@arinc9.com>
Date: Sun, 4 Feb 2024 20:14:27 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Daniel Golle <daniel@...rotopia.org>, DENG Qingfang <dqfext@...il.com>,
 Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
 Florian Fainelli <f.fainelli@...il.com>, Vladimir Oltean
 <olteanv@...il.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
 Bartel Eerdekens <bartel.eerdekens@...stell8.be>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next v3 4/7] net: dsa: mt7530: move XTAL check to
 mt7530_setup()

On 4.02.2024 20:07, Russell King (Oracle) wrote:
> On Sun, Feb 04, 2024 at 07:51:49PM +0300, Arınç ÜNAL wrote:
>> On 4.02.2024 19:38, Russell King (Oracle) wrote:
>>> On Sun, Feb 04, 2024 at 06:55:14PM +0300, Arınç ÜNAL wrote:
>>>> On 4.02.2024 17:18, Russell King (Oracle) wrote:
>>>>> On Sun, Feb 04, 2024 at 04:55:40PM +0300, Arınç ÜNAL wrote:
>>>>>> This is not about laziness. This is before patch 2:
>>>>>>
>>>>>> phylink_mac_ops :: mac_config() -> dsa_port_phylink_mac_config()
>>>>>> -> dsa_switch_ops :: phylink_mac_config() -> mt753x_phylink_mac_config()
>>>>>>       -> mt753x_mac_config()
>>>>>>          -> mt753x_info :: mac_port_config() -> mt7530_mac_config()
>>>>>>             -> mt7530_setup_port5()
>>>>>>       -> mt753x_pad_setup()
>>>>>>          -> mt753x_info :: pad_setup() -> mt7530_pad_clk_setup()
>>>>>>
>>>>>> This is after:
>>>>>>
>>>>>> phylink_mac_ops :: mac_config() -> dsa_port_phylink_mac_config()
>>>>>> -> dsa_switch_ops :: phylink_mac_config() -> mt753x_phylink_mac_config()
>>>>>>       -> mt753x_mac_config()
>>>>>>          -> mt753x_info :: mac_port_config() -> mt7530_mac_config()
>>>>>>             -> mt7530_setup_port5()
>>>>>>             -> mt7530_setup_port6()
>>>>>>
>>>>>> Patch 2 does not move mt7530_setup_port6() to be called from
>>>>>> phylink_mac_ops :: mac_config(), it already is. There is no valid reason to
>>>>>> reorder the patches.
>>>>>>
>>>>>> My response to Russell should've stated this instead of focusing on his
>>>>>> second sentence.
>>>>>
>>>>> This patch moves the test for a 20MHz crystal to mt7530_setup(),
>>>>> which is something that is entirely orthogonal to patch 2, which
>>>>> can be done cleanly (I've just applied the patches in the original
>>>>> order and then reordered them:
>>>>>
>>>>> 98c481f5d706 net: dsa: mt7530: do not clear config->supported_interfaces
>>>>> 93c6b53b17f4 net: dsa: mt7530: correct port capabilities of MT7988
>>>>> c9c6d4c51a1d net: dsa: mt7530: simplify mt7530_setup_port6() and change to void
>>>>> adfa948253e0 net: dsa: mt7530: remove pad_setup function pointer
>>>>> 57e21e6c2fc0 net: dsa: mt7530: call port 6 setup from mt7530_mac_config()
>>>>> 959a0f9323c8 net: dsa: mt7530: move XTAL check to mt7530_setup()
>>>>> 856ab64a22ef net: dsa: mt7530: empty default case on mt7530_setup_port5()
>>>>>
>>>>> No problems. The end result is identical comparing the git tree at the
>>>>> original "move XTAL" patch with adfa948253e0.
>>>>>
>>>>> Now, if we look at "net: dsa: mt7530: remove pad_setup function pointer"
>>>>> we can see that yes, the pad_setup() method was called from mac_confing,
>>>>> but this is the exact contents of that patch removing the callsite:
>>>>>
>>>>> -               mt753x_pad_setup(ds, state);
>>>>>
>>>>> This returns an integer, which may be an error code, which is ignored.
>>>>> Therefore, if the XTAL frequency check fires, and mt753x_pad_setup()
>>>>> returns an error, it is ignored today.
>>>>>
>>>>> After "net: dsa: mt7530: call port 6 setup from mt7530_mac_config()"
>>>>> the renamed pad_setup() method is now called from mac_config() thusly:
>>>>>
>>>>> +               ret = mt7530_setup_port6(priv->ds, interface);
>>>>> +               if (ret)
>>>>> +                       return ret;
>>>>>
>>>>> So now the error checks cause mt7530_mac_config() to return an error
>>>>> which in turn causes mt753x_mac_config() to fail, and therefore
>>>>> mt753x_phylink_mac_config() has different behaviour.
>>>>>
>>>>> So, patch 2 changes the driver behaviour in the case of a 20MHz XTAL,
>>>>> which is then changed again by patch 4.
>>>>>
>>>>> It would be better to have only one change of behaviour by moving
>>>>> patch 4 before patch 2.
>>>>
>>>> If the idea is to not bring any more error returns to mt753x_mac_config()
>>>> because the return code is actually checked for that, I should do a bit
>>>> more effort and put patch 5 before patch 2 as well, to live up to what you
>>>> originally requested.
>>>
>>> I assume you are referring to getting rid of the default case in
>>> mt7530_pad_clk_setup().
>>>
>>> In patch "net: dsa: mt7530: call port 6 setup from mt7530_mac_config()"
>>> where you move this to be called from mt7530_mac_config(), you add it
>>> as:
>>>
>>> +       } else if (port == 6) {
>>> +               ret = mt7530_setup_port6(priv->ds, interface);
>>> +               if (ret)
>>> +                       return ret;
>>> +       }
>>>
>>> So it is only called for port 6. The switch within the called function
>>> deals with PHY_INTERFACE_MODE_RGMII and PHY_INTERFACE_MODE_TRGMII.
>>> Anything else results in the use of the default case, and thus
>>> returning an error.
>>>
>>> Since mt7530_mac_port_get_caps() does this for port 6:
>>>
>>>                   __set_bit(PHY_INTERFACE_MODE_RGMII,
>>>                             config->supported_interfaces);
>>>                   __set_bit(PHY_INTERFACE_MODE_TRGMII,
>>>                             config->supported_interfaces);
>>>
>>> mt7530_setup_port6() will only ever be called for these two modes,
>>> which means that the default case is unreachable, thus we will never
>>> execute that path, thus whether that path returns an error or not is
>>> completely irrelevant.
>>>
>>> The only case in mt7530_setup_port6() / mt7530_pad_clk_setup() which
>>> can today return an error is the XTAL check.
>>>
>>> Therefore, my suggestion makes complete sense, and there is no need
>>> to also move patch 5.
>>
>> Understood. I've already submitted v4 which moves patch 5. The remaining
>> benefit is that there're fewer code changes as I don't need to add an error
>> return for mt7530_setup_port6() and then remove it.
> 
> I'm pretty sure netdev has a rule _not_ to submit the next version of
> a patch series if discussion about the previous is still ongoing...
> but I can't find any of the netdev rules in Documentation/networking
> anymore, and nothing stands out in Documentation/process... ah,
> Documentation/process/maintainer-netdev.rst, and here we are:
> 
> "Make sure you address all the feedback in your new posting. Do not post
> a new
> version of the code if the discussion about the previous version is
> still
> ongoing, unless directly instructed by a reviewer."
> 
> Discussion was still ongoing over this point, so ideally you should
> have waited instead of presenting a fait-accompli _during_ the
> ongoing discussion.

Thank you for bringing this to my attention. Next time I will be more
careful when deciding whether the discussion was over.

Arınç

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