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

[Andreas Färber]

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.

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.

Regards,
Andreas

-- 
SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)