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

Mon Sep 24 14:56:01 UTC 2018

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.

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 ?

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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