Re: [PATCH net] Revert "net: stmmac: platform: Fix MDIO init for platforms without PHY"

[Robin Murphy <robin.murphy@arm.com>]

On 07/01/2020 12:14 pm, Sriram Dash wrote:
>> From: Robin Murphy <robin.murphy@arm.com>
>> Subject: Re: [PATCH net] Revert "net: stmmac: platform: Fix MDIO init for
>> platforms without PHY"
>>
>> On 07/01/2020 5:46 am, Sriram Dash wrote:
>>>> From: Florian Fainelli <f.fainelli@gmail.com>
>>>> Subject: [PATCH net] Revert "net: stmmac: platform: Fix MDIO init for
>>> platforms
>>>> without PHY"
>>>>
>>>> This reverts commit d3e014ec7d5ebe9644b5486bc530b91e62bbf624 ("net:
>>>> stmmac: platform: Fix MDIO init for platforms without PHY") because
>>>> it
>>> breaks
>>>> existing systems with stmmac which do not have a MDIO bus sub-node
>>>> nor a 'phy-handle' property declared in their Device Tree. On those
>>>> systems, the stmmac MDIO bus is expected to be created and then
>>>> scanned by
>>>> of_mdiobus_register() to create PHY devices.
>>>>
>>>> While these systems should arguably make use of a more accurate
>>>> Device
>>> Tree
>>>> reprensentation with the use of the MDIO bus sub-node an appropriate
>>>> 'phy- handle', we cannot break them, therefore restore the behavior
>>>> prior to the
>>> said
>>>> commit.
>>>>
>>>> Fixes: d3e014ec7d5e ("net: stmmac: platform: Fix MDIO init for
>>>> platforms without PHY")
>>>> Reported-by: Heiko Stuebner <heiko@sntech.de>
>>>> Reported-by: kernelci.org bot <bot@kernelci.org>
>>>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>>> Nacked-by: Sriram Dash <Sriram.dash@samsung.com>
>>>
>>>> ---
>>>> Heiko,
>>>>
>>>> I did not add the Tested-by because the patch is a little bit
>>>> different
>>> from what
>>>> you tested, even if you most likely were not hitting the other part
>>>> that I
>>> was
>>>> changing. Thanks!
>>>>
>>>>    drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> index cc8d7e7bf9ac..bedaff0c13bd 100644
>>>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
>>>> @@ -320,7 +320,7 @@ static int stmmac_mtl_setup(struct
>>>> platform_device *pdev,  static int stmmac_dt_phy(struct
>> plat_stmmacenet_data *plat,
>>>>    			 struct device_node *np, struct device *dev)  {
>>>> -	bool mdio = false;
>>>> +	bool mdio = true;
>>>
>>>
>>> This is breaking for the platforms with fixed-link.
>>> stih418-b2199.dts and 169445.dts to name a few.
>>>
>>> For the newer platforms, they should provide the mdio/ snps,dwmac-mdio
>>> property in the device tree as we are checking the mdio/
>>> snps,dwmac-mdio property in the stmmac_platform driver for the mdio bus
>> memory allocation.
>>> For existing platforms, I agree we should not break them, but we
>>> should make the code correct. And make the existing platforms adapt to the
>> proper code.
>>> There is a proposed solution.
>>> https://protect2.fireeye.com/url?k=d075c0fc-8da69942-d0744bb3-0cc47a31
>>> ba82-60be9f5a0fb38a27&u=https://lkml.org/lkml/2020/1/7/14
>>>
>>> What do you think?
>>
>> The binding says that the phy handle and mdio child node are optional, so
>> "update all of the DTBs!" is not a viable solution. I'm far from an expert here, but
> 
> I get your point Robin. Because the mdio child or snps,dwmac-mdio is not mandatory,
> there has been this problem.
> 
>> AFAICS the fault of the current code is that it assumes the lack of a phy handle
>> implies a fixed link, so the obvious answer is to actually check whether the
> 
> Kind of.
> 
>> "fixed-link" property is present.
> 
> 
> I agree to have a fixed link check. Possibly this can be done:

FWIW, given the 4th case in the kerneldoc table I think this check might 
need to come first. On the upside, there appears to be a handy helper 
already, so it may just be as simple as:

	bool mdio = !of_phy_is_fixed_link(np);

Robin.

> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> @@ -320,7 +320,9 @@ static int stmmac_mtl_setup(struct platform_device *pdev,
>   static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
>                           struct device_node *np, struct device *dev)
>   {
> -       bool mdio = false;
> +       bool mdio = true;
> +       struct device_node *fixed_link;
> +
>          static const struct of_device_id need_mdio_ids[] = {
>                  { .compatible = "snps,dwc-qos-ethernet-4.10" },
>                  {},
> @@ -340,9 +342,8 @@ static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
>                  }
>          }
> 
> -       if (plat->mdio_node) {
> -               dev_dbg(dev, "Found MDIO subnode\n");
> -               mdio = true;
> +       if (of_get_child_by_name(np, "fixed-link")) {
> +               mdio = false;
>          }
> 
>          if (mdio) {
> 
> Neil and Heiko,
> 
> Can you guys please test this on your platforms?
> We can post a more cleaner version of the patch if all agree to it.
> 
>>
>> Robin.
>>
>>>
>>>>    	static const struct of_device_id need_mdio_ids[] = {
>>>>    		{ .compatible = "snps,dwc-qos-ethernet-4.10" },
>>>>    		{},
>>>> --
>>>> 2.19.1
>>>
>>>
>>>
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>