[U-Boot] [PATCH] serial: ns16550: Fix serial output on Tegra186

[Alexandre Courbot]

Hi Paul,

On 09/30/2016 06:47 PM, Paul Burton wrote:
> * PGP Signed by an unknown key
> 
> On Friday, 30 September 2016 17:53:38 BST Alexandre Courbot wrote:
>> On 09/30/2016 05:46 PM, Thierry Reding wrote:
>>> From: Thierry Reding <treding at nvidia.com>
>>>
>>> For Tegra186 there are currently no UART clocks wired up in device tree.
>>> This exposes a regression introduced in commit 50fce1d5d874 ("serial:
>>> ns16550: Support clocks via phandle"), which causes the p2771-0000-500
>>> board (and probably any Tegra186-based board as well) to fail to boot.
>>>
>>> The reason is that if no clocks property exists, then clk_get_by_index()
>>> returns -ENOENT (via fdtdec_parse_phandle_with_args()) rather than
>>> -ENODEV as the above-mentioned commit expects.
>>>
>>> Fix this by checking for the right error code.
>>
>> Tested-by: Alexandre Courbot <acourbot at nvidia.com>
>>
>> I sent a similar patch ~10 minutes before this one, but Thierry's commit
>> message is clearer than mine (and his handling of -ENODEV probably more
>> correct as well), so let's go with this version!
> 
> 
> Hi Thierry & Alexandre,
> 
> Apologies for the breakage!
> 
> If a DT contains a clock & the UART node references it by phandle then I 
> believe clk_get_by_index() could return -ENODEV via 
> uclass_get_device_by_of_offset & uclass_find_device_by_of_offset. So we 
> probably need to handle both -ENOENT for the "no clocks property" case & -
> ENODEV for the "clocks property but no driver" case, as Alexandre's patch 
> does?

But if a DT contains a clock, shouldn't it simply take precedence over
the legacy method? (not very familiar with this code so my comment may
not make sense).

IOW, do we have a case where clk_get_by_index() returns -ENODEV and
fdtdec_get_int() returns a valid clock?