[PATCH] usb: cdns3: fix cdns3_bind() to avoid returning error and probe parent

[Marek Vasut]

On 3/4/26 7:46 AM, Siddharth Vadapalli wrote:
> On 03/03/26 19:37, Marek Vasut wrote:
>> On 3/1/26 6:25 AM, Siddharth Vadapalli wrote:
>>
>>>>> There are two users of cdns3_bind() which have registered their 
>>>>> own .bind() callback as cdns3_bind():
>>>>> 1. cdns3-starfive.c driver
>>>>> 2. cdns3-ti.c driver
>>>>> Since .bind() is called before .probe()
>>>>
>>>> .bind callback is meant to BIND the driver instance (to a DT node), 
>>>> it is not meant to initialize the hardware. .probe callback is meant to 
>>>
>>> I agree. But that's exactly where the issue lies. When 'dr_mode' is 
>>> set to OTG, cdns3_bind() is unable to determine if the driver to bind 
>>> to the DT node is "cdns-usb3-host" or "cdns-usb3-peripheral".
>>>
>>> Since [0], we attempt to identify if OTG should imply 'peripheral' or 
>>> 'host'. But to do that, [0] needs to read the VBUS Valid field of the 
>>> OTG Status register. And register access requires the USB Controller 
>>> to be powered ON.
>>
>> Correct, so bind is the wrong place to do any HW access .
>>
>>> [0]: bfb530e06ca6 ("usb: cdns3: use VBUS Valid to determine role for 
>>> dr_mode OTG")
>>>
>>>> initialize the hardware. This is fundamental part of the U-Boot DM 
>>>> lazy initialization scheme. If something does initialize hardware 
>>>> in .bind, then it is very likely wrong.
>>>>
>>>>> , and, since cdns3_bind() is also the .bind() callback of the above 
>>>>> drivers, device_probe() has to be added here itself. Moreover, it 
>>>>> is only due to the register accesses being performed by the 
>>>>> recently introduced cdns3_get_otg_mode() function that we need the 
>>>>> USB Controller to be powered ON at this stage.
>>>> So, can we fix this so the HW initialization won't be happening in 
>>>> bind, but instead in .probe ?
>>>
>>> That isn't possible
>>
>> Can you investigate how to make that possible ? Maybe by having some 
>> common .probe implementation that would determine the OTG state, or by 
>> having some stub driver which handles the OTG selection ?
> A common .probe will not work because the .id has to be either
> UCLASS_USB_GADGET_GENERIC OR UCLASS_USB
> for the new stub driver (say cdns-usb3-otg). By fixing .id beforehand, 
> we will always fail to probe the driver for the case where the desired 
> role is the opposite of the role corresponding to .id.

Looking at this one more time, drivers/usb/cdns3/cdns3-ti.c is already 
UCLASS_NOP , that is the parent driver that you are trying to probe in 
bind here, right ?

Could you instead flag that cdns3-ti.c with dev_or_flags(dev, 
DM_FLAG_PROBE_AFTER_BIND); so it would probe early ? Would that resolve 
this problem too ?

And just a follow up idea, if you were to stop DM scan at DT compatible 
= "ti,j721e-usb"; in 
dts/upstream/src/arm64/ti/k3-j784s4-j742s2-main-common.dtsi (i.e. the 
cdns3 driver wouldn't bind at all), maybe you could make the cdns3-ti.c 
bind the right driver (peripheral or host) the same way e.g. block 
device partitions or USB devices are bound during 'mmc rescan' or 'usb 
reset' . All those devices are instantiated after the initial DM scan 
and after the controller to which they are attached has been probed. 
This might be the way to avoid probe in bind too ?