Re: [PATCH 10/12] platform/early: implement support for early platform drivers

[Rob Herring]

On Tue, May 15, 2018 at 9:06 AM, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> 2018-05-14 15:37 GMT+02:00 Rob Herring <robh+dt@xxxxxxxxxx>:
>> On Fri, May 11, 2018 at 11:20 AM, Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
>>> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
>>>
>>> This introduces the core part of support for early platform drivers
>>> and devices.
>>>
>>
>> It looks like most of your prep patches are to separate the alloc and
>> init of platform devices because you are essentially making early
>> devices/drivers a sub-class. Maybe you could avoid doing that and
>> simplify things a bit. Comments below based on doing that...
>>
>
> My aim was to change as little as possible for everybody else while
> fixing our problem. These changes are already controversial enough
> without risky reusing of existing fields in common structures. I was
> just afraid that there are too many intricacies for it to be safe.

I don't think those intricacies would go away just by having separate
fields. Perhaps it would make things fail more explicitly. After all,
I think it needs to be a very atomic operation when a device is
switched.

>>> +/**
>>> + * struct early_platform_driver
>>> + *
>>> + * @pdrv: real platform driver associated with this early platform driver
>>> + * @list: list head for the list of early platform drivers
>>> + * @early_probe: early probe callback
>>> + */
>>> +struct early_platform_driver {
>>> +       struct platform_driver pdrv;
>>> +       struct list_head list;
>>
>> Couldn't you use an existing list in driver_private until you move
>> over to the normal bus infra.
>>
>
> This is something that the previous implementation did. It was quite
> unreadable, so I decided to go with a separate list.
>
>>> +       int (*early_probe)(struct platform_device *);
>>
>> Just add this to platform_driver.
>>
>
> This would extend the structure for everybody else while there'll be
> very few such devices and not all systems would even require it.
>
>>> +};
>>> +
>>> +/**
>>> + * struct early_platform_device
>>> + *
>>> + * @pdev: real platform device associated with this early platform device
>>> + * @list: list head for the list of early platform devices
>>> + * @deferred: true if this device's early probe was deferred
>>> + * @deferred_drv: early platform driver with which this device was matched
>>> + */
>>> +struct early_platform_device {
>>> +       struct platform_device pdev;
>>> +       struct list_head list;
>>
>> Use a list in device_private?
>>
>>> +       bool deferred;
>>> +       struct early_platform_driver *deferred_drv;
>>
>> Can't you use the existing deferred probe list?
>>
>
> I thought about it, but I was afraid there could be some timing issues
> with that and decided against it. The early deferral also doesn't work
> in a workque, but is synchronous instead.

I didn't mean use the wq, but just the list fields. You'd still have
the early list and normal list with different list heads. If you ever
had a device wanting to be on both lists at the same time, then you've
got major problems.

Rob