Message-ID: <850064fb-59c6-4e07-962a-6a213e9e7f90@arinc9.com>
Date: Sun, 4 Feb 2024 19:51:49 +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 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.

Arınç

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