[U-Boot] [PATCH] common: add board specific hook for os preboot config

[Stefan Agner]

On 24.09.2018 16:56, Michael Nazzareno Trimarchi wrote:
> Hi
> 
> On Mon., 24 Sep. 2018, 4:51 pm Stefan Agner, <stefan at agner.ch> wrote:
> 
>> On 24.09.2018 16:43, Michael Nazzareno Trimarchi wrote:
>>> Hi
>>>
>>> On Thu., 16 Aug. 2018, 3:09 pm Stefan Agner, <stefan at agner.ch>
>> wrote:
>>>
>>>> On 13.08.2018 09:30, Gerard Salvatella wrote:
>>>>> Some boards require specific configuration prior to booting the
>>>> kernel.
>>>>> For instance, our boards require shutting down the display to
>>>> avoid
>>>>> fading transitions before the drivers are reloaded by the
>> kernel.
>>>> This
>>>>> could be facilitated by adding an extra hook during the os
>> booting
>>>>> process.
>>>>
>>>> Maybe I can extend on what we are trying to achieve here:
>>>>
>>>> We enable display backlight using board code.
>>>
>>> You can make it works almost easily.
>>>
>>> I enable simple fb, inject allocated display parameters in dts to
>>> reserve area, pass the area to the graphics controller and dismiss
>> it
>>> during probing
>>>
>>> This is mainline in linux support.
>>>
>>> I have couple of patches need to clean up for imx architecture
>>> (imx6ull and imx25)
>>
>> Definitely interested in those patches! Of course using this
>> approach
>> leads to the most seamless booting experience.
> 
> Yes but there are a lot of reason to have when you deal multi-image
> update and so on.
> 
>> But as far as I know it also needs proper (driver specific) Linux
>> support, is that correct?
> 
> No that is wrong. imx6ull need a small patches right now I have
> applied in kernel in legacy driver and not in drm one. 
> 

In what way is that different to what I wrote above?

In the end, the OS needs support for this.

> sunxi already implement everything in their side
> 
>> So, I think its anyway worth having an option to properly disable
>> the
>> display and backlight for older kernels/non-Linux OS.
> 
> gpio clear gpio-6 ; bootm ?

That is very board specific scripting required. We enable the backlight
in code, so we should disable it, especially if we disable the
controller (which we do currently).

--
Stefan

> 
> Michael
> 
>> --
>> Stefan
>>
>>>
>>> You can still scripting it using cmd interface
>>>
>>> Michael
>>>
>>>> The architecture code then shuts down the display controller just
>>>> before
>>>> booting Linux (e.g. on i.MX, by calling
>>>> ipuv3_fb_shutdown/lcdif_power_down in arch_preboot_os).
>>>>
>>>> This leads to a display which has backlight enabled, but no data
>>>> driven... Depending on display this leads to noisy/fading
>>>> transitions
>>>> between U-Boot and Linux.
>>>>
>>>> So we would like to disable the backlight in board code.
>>>>
>>>> In a first version we used a weak display_shutdown() function,
>> but
>>>> with
>>>> that we would have to add it to every architecture.
>>>>
>>>> This approach uses a generic board specific preeboot_os callback
>>>> which
>>>> can be used for different purpose too.
>>>>
>>>> Does this sound like an approach which is acceptable upstream?
>>>>
>>>> --
>>>> Stefan
>>>>
>>>>>
>>>>> Signed-off-by: Gerard Salvatella <gerard.salvatella at toradex.com>
>>>>> ---
>>>>> common/bootm_os.c | 7 +++++++
>>>>> 1 file changed, 7 insertions(+)
>>>>>
>>>>> diff --git a/common/bootm_os.c b/common/bootm_os.c
>>>>> index f4bd905909..1e7af56b64 100644
>>>>> --- a/common/bootm_os.c
>>>>> +++ b/common/bootm_os.c
>>>>> @@ -505,9 +505,16 @@ __weak void arch_preboot_os(void)
>>>>> /* please define platform specific arch_preboot_os() */
>>>>> }
>>>>>
>>>>> +/* Allow for board specific config before we boot */
>>>>> +__weak void board_preboot_os(void)
>>>>> +{
>>>>> +       /* please define board specific board_preboot_os() */
>>>>> +}
>>>>> +
>>>>> int boot_selected_os(int argc, char * const argv[], int state,
>>>>> bootm_headers_t *images, boot_os_fn *boot_fn)
>>>>> {
>>>>> +       board_preboot_os();
>>>>> arch_preboot_os();
>>>>> boot_fn(state, argc, argv, images);
>>>>>
>>>>> --
>>>>> 2.18.0
>>>>>
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