Re: [PATCH 0/4] net: ti: am65-cpsw-nuss: Fix DT binding handling of pinctrl

[Ravi Gunasekaran <r-gunasekaran@ti.com>]

Maxime,

On 7/20/23 7:42 PM, Maxime Ripard wrote:
> Hi
> 
> Sorry, I didn't receive Roger mail so I'll reply here
> 
> On Thu, Jul 20, 2023 at 09:00:19AM -0500, Nishanth Menon wrote:
>> On 16:56-20230720, Roger Quadros wrote:
>>> Hi,
>>>
>>> On 20/07/2023 16:33, Ravi Gunasekaran wrote:
>>>>
>>>>
>>>> On 7/20/2023 3:25 PM, Maxime Ripard wrote:
>>>>> Hi,
>>>>>
>>>>> This series is based on:
>>>>> https://lore.kernel.org/all/20230713072019.3153871-1-nm@ti.com/
>>>>>
>>>>> It fixes the issue of Linux booting from the DT embedded by U-boot. The
>>>>> main issue there is that U-Boot doesn't handle the MDIO child node that
>>>>> might have resources attached to it.
>>>>>
>>>>> Thus, any pinctrl configuration that could be attached to the MDIO
>>>>> child node is effectively ignored. Unfortunately, starting with 6.5-rc1,
>>>>> Linux does just that.
>>>
>>> I didn't get this part. Linux does not ignore pinctrl configuration attached
>>> to MDIO child node. What changed in 6.5-rc1?
> 
> Linux doesn't ignore it, but Linux started putting pinctrl configuration
> on the MDIO node, which is ignored by U-Boot.
> 
>>>>> This was solved by duplicating the pinctrl configuration onto the MAC
>>>
>>> If I remember right, there is no driver model driver for MDIO in u-boot and
>>> adding the mdio pinctrl into CPSW DT node was a hack in u-boot.
> 
> Yeah, but we now have in the U-Boot DT two nodes referencing the same
> pinctrl configuration: the CPSW and the MDIO node. Linux then tries to
> assign that configuration to both devices and it fails.

This response might be late, as I know things have moved ahead after this
discussion. But I just wanted to understand the root cause little bit more.
Is the issue mainly because the same mdio pinctrl node(phandle) is referenced in
two other nodes? Or is it because of same pins being updated in two different
places in the kernel?

If it is the former, then would a duplicate mdio node help keep the changes
to minimum?


> 
>>>>> device node. Unfortunately, this doesn't work for Linux since now it has
>>>>> two devices competing for the same pins.
>>>
>>> What has really changed here is that you are passing u-boot's device
>>> tree to Linux.
> 
> I didn't change anything. This is the default boot process if you don't
> provide a DT in the ESP partition.
> 
>>> This has nothing to do with 6.5-rc1 right?
> 
> The issue started to occur with Nishanth patch to sync with Linux
> 6.5-rc1 device trees, so there's definitely a connection.
> 
>>> I suppose your solution is still a hack but of lesser evil than
>>> duplicating MDIO pinctrl in CPSW node.
>>>
>>> The proper solution would be to implement driver model for the
>>> davinci MDIO driver. Siddharth has been working on this. If that is
>>> close to ready we should just use that instead.
>>
>> But this allows for a cleaner device tree while the driver can be fixed
>> up independently, correct? Unfortunately, Siddharth's driver model work,
>> from what I understand, is around 2024 timeframe.. which is probably not
>> something that helps us in the community at this point.
> 
> Yeah, at the moment I have to choose between getting the MMC to work in
> Linux or the Ethernet ports. The former is working thanks to your patch,
> the latter is broken because of it. Ideally I'd like both :)
> 
> Maxime

-- 
Regards,
Ravi