[U-Boot] [PATCH v2 1/1] core/uclass: iterate over all devices of a uclass

[Simon Glass]

Hi Andreas,

On 19 April 2017 at 10:37, Andreas Färber <afaerber at suse.de> wrote:
> Am 19.04.2017 um 17:52 schrieb Simon Glass:
>> Hi Andreas,
>>
>> On 19 April 2017 at 09:14, Simon Glass <sjg at chromium.org> wrote:
>>> Hi Andreas,
>>>
>>> On 19 April 2017 at 08:43, Andreas Färber <afaerber at suse.de> wrote:
>>>> Hi Simon,
>>>>
>>>> Am 19.04.2017 um 16:28 schrieb Simon Glass:
>>>>> On 19 April 2017 at 05:26, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>>>>>> When iterating over the devices of an uclass the iteration stops
>>>>>> at the first device that cannot be probed.
>>>>>> When calling booefi this will result in no block device being
>>>>>> passed to the EFI executable if the first device cannot be probed.
>>>>>>
>>>>>> The problem was reported by Andreas Färber in
>>>>>> https://lists.denx.de/pipermail/u-boot/2017-April/287432.html
>>>>>>
>>>>>> For testing I used an odroid-c2 with a dts including
>>>>>> &sd_emmc_a {
>>>>>>         status = "okay";
>>>>>> }
>>>>>> This device does not exist on the board and cannot be initialized.
>>>>>>
>>>>>> With the patch uclass_first_device and uclass_next_device
>>>>>> iterate internally until they find the first device that can be
>>>>>> probed or the end of the device list is reached.
>>>>>
>>>>> I would like to avoid changing the API that much. Can you please
>>>>> change it to stop calling the tail function and always set the device,
>>>>> like you did in v1?
>>>>
>>>> I fear you're missing the key point I made in my lengthy explanation:
>>>
>>> That's not entirely impossible.
>>>
>>>>
>>>> Our caller (EFI) wants to iterate over the available devices. SDIO is
>>>> not available. If we return a non-NULL device it will try to scan the
>>>> disk. Therefore I think v2 is more correct (not yet tested).
>>>>
>>>> So really the question is what your desired semantics of this function
>>>> are and how callers here and elsewhere are handling it. If we want to
>>>> return non-probed devices to the caller, as you now suggest, then we
>>>> would need to audit and amend all callers of the API with some "if
>>>> !is_probed() then continue" check. If we simply skip them internally, as
>>>> done here IIUC, we require no changes on the caller side, thus much less
>>>> invasive.
>>>
>>> Well the value of 'ret' gives you that information if you want it. But
>>> yes it is a change and on second thoughts I'm not entirely comfortable
>>> with it.
>>>
>>>>
>>>> Maybe we need a new API uclass_{first,next}_available_device() to make
>>>> this clear? The change would then only affect callers of the new API,
>>>> and EFI and possibly others would again need to be audited and updated.
>>
>> If you think this is generally useful then you could add this. I think
>> it would be something like:
>>
>> for (ret = uclass_first_avail_device(UCLASS_..., &dev; dev; ret =
>> uclass_next_avail_device(&dev)) {
>>     if (!ret) {
>>        // do something
>>    }
>> }
>>
>> Does that sounds right?
>
> No. I think that should be the semantics of uclass_first_device(), i.e.
> Heinrich's v1, possibly moved out of _tail() as you requested.
>
> The idea behind a separate ..._available_device() implementation was to
> not have to do that ret check and to simply replace the function name to
> change the semantics, i.e. Heinrich's v2 implementation, but not inside
> uclass_{first,next}_device() but in copies with different name.

How do you know what the error was? If you return a 'dev' then how do
you know whether it is OK to process it? I'd prefer that this is
provided via the return value rather than checking device_active(),
etc.

>
> What use case is there for an incomplete enumeration as done by
> uclass_first_device() today? In order to continue enumeration devp needs
> to be set IIUC.

The existing API returns a NULL device when it gets an error, meaning
that the device cannot be used. The use case is for devices which
don't fail on probe. While I understand that removeable devices can
fail to probe today and then succeed later, many devices are not like
that, and failing to probe is an error.

Regards,
Simon