[U-Boot] [PATCH] pci: restore initialization for DM_PCI

[Stephen Warren]

On 01/22/2016 01:32 PM, Simon Glass wrote:
> Hi Stephen,
>
> On 22 January 2016 at 12:38, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>
>> On 01/21/2016 09:03 PM, Simon Glass wrote:
>>>
>>> Hi Bin,
>>>
>>> On 21 January 2016 at 20:53, Bin Meng <bmeng.cn at gmail.com> wrote:
>>>>
>>>> On Fri, Jan 22, 2016 at 11:36 AM, Simon Glass <sjg at chromium.org> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> On 21 January 2016 at 18:39, Bin Meng <bmeng.cn at gmail.com> wrote:
>>>>>>
>>>>>> Hi Stephen,
>>>>>>
>>>>>> On Fri, Jan 22, 2016 at 7:35 AM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>>>>>>
>>>>>>> From: Stephen Warren <swarren at nvidia.com>
>>>>>>>
>>>>>>> PCI controllers should be enumerated at startup so that PCI devices
>>>>>>> such as Ethernet controllers are available at startup. Fix board_init_r()
>>>>>>> not to skip calling pci_init() when CONFIG_DM_PCI is defined, and provide
>>>>>>> an implementation of pci_init() for the DM case.
>>>>>>>
>>>>>>
>>>>>> What exact issue are you trying to fix? I posted the same question on
>>>>>> Simon's patch [1] before. Does your patch and Simon's fix the same
>>>>>> issue?
>>>>>>
>>>>>> Note I submitted a similar patch [2] last year for x86 only, to
>>>>>> explicitly trigger the PCI enueration. But it was not accepted.
>>>>>>
>>>>>>> Fixes: 96350f729c42 ("dm: tegra: net: Convert tegra boards to driver model
>>>>>>> for Ethernet")
>>>>>>> Signed-off-by: Stephen Warren <swarren at nvidia.com>
>>>>>>> ---
>>>>>>> I'm not sure if relying on the side-effects of calling
>>>>>>> uclass_{first,ext}_device is the correct approach; is there a more explicit
>>>>>>> way to probe all PCI controllers?
>>>>>>>
>>>>>>> Arguably, perhaps we should introduce a "pci start" command instead of
>>>>>>> this change to be consistent with e.g. USB. However, that would be a
>>>>>>> regression relative to earlier versions of U-Boot.
>>>>>>> ---
>>>>>>
>>>>>>
>>>>>> [1] http://patchwork.ozlabs.org/patch/569323/
>>>>>> [2] http://patchwork.ozlabs.org/patch/500246/
>>>>>>
>>>>>> Regards,
>>>>>> Bin
>>>>>
>>>>>
>>>>> This does go against the driver-model philosophy of lazy init. I
>>>>> wonder if we should add this patch with a Kconfig option to enable it?
>>>>> Then it can be enabled only for boards that need it.
>>>>>
>>>>
>>>> I suspect the issue is somewhere else. On Intel Galileo with a PCI
>>>> ethernet, it works fine without such explicit pci init. Which PCI
>>>> ethernet driver does not work on Tegra?
>>>
>>>
>>> It could be because that board probes PCI to get its serial to work.
>>>
>>> This could be fixed on Tegra by adding an Ethernet node to the device
>>> tree to cause it to be probed. But I don't think that should be a
>>> requirement.
>>
>>
>> Since PCI devices are automatically probed via standard bus protocols, I believe we shouldn't have to add them to the DT.
>>
>> However, I could accept that we should add the PCI controller to DT in order for the controller to be probed, and when that happens, the bus should be enumerated thus causing all the Ethernet devices to be probed. However, the PCI controller is already in DT, and this process isn't being kicked off, so if that's the way it's supposed to work, there's a bug there.
>
> So what do you think about a Kconfig option that tells U-Boot that PCI
> must be probed after relocation?

I'm puzzled why anyone would turn off that option.

If PCI is to be used at all, it needs to be probed. The only way I'm 
aware of that it can be probed today is by accidental side-effect of 
some board forcibly probing some device that happens to be on a PCI bus 
(i.e. Bin's case). In other case, PCI doesn't get automatically probed 
at boot, and I don't see any command that allows it to be probed 
manually. Don't we need this patch (or your patch linked above) in order 
to make PCI usable at all? If so, why would anyone turn this off?