[RFC 0/3] drm/msm+clk: handover of bootloader display

[Geert Uytterhoeven]

Hi Rob,

On Tue, Jul 11, 2017 at 8:20 PM, Rob Clark <robdclark at gmail.com> wrote:
> So now that this is working (at least on a single device), I figured
> it was a good time to send out an RFC to start discussion about how
> to do this properly, in particular the CCF/powerdomain parts.
>
> The first patch adds flags so we can mark power domains and leaf
> node clocks which might (or might not) be enabled by bootloader and
> which we want to inherit when real display driver is probed.  (There
> might be use-cases outside of display.. such as debug serial port?
> I guess display is the most common/complex/useful use-case.)  From
> the CCF/genpd standpoint, "inherit" really just means "fixup enable/
> prepare_count and don't automatically switch off in lateinit".  The
> rest of the complexity is in the display driver.
>
> For display, there are two different cases depending on whether the
> display driver is built as a module (ie. probes after lateinit) or
> not.  If the display driver is built as a module, then we want efifb
> to keep working after the clk_disable_unused + genpd_power_off_unused
> late_initcall's.  And in either case, we want the display driver to
> be able to detect that display is already on (by checking whether
> various clocks are already enabled) so that it knows to readback the
> hw state.  (And not try to do things like clk_set_rate() on already
> running clocks.)

For the PM domains: won't these just stay enabled if efifb would
call pm_runtime_enable() and pm_runtime_get_sync()?

For clocks, can't efifb enable all clocks tied to the device in DT?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds