[PATCH v5 21/27] clk: bcm: rpi: Discover the firmware clocks

[Stephen Boyd]

Quoting Maxime Ripard (2020-06-15 01:41:01)
> The RaspberryPi4 firmware actually exposes more clocks than are currently
> handled by the driver and we will need to change some of them directly
> based on the pixel rate for the display related clocks, or the load for the
> GPU.
> 
> Since the firmware implements DVFS, this rate change can have a number of
> side-effects, including adjusting the various PLL voltages or the PLL
> parents. The firmware also implements thermal throttling, so even some
> thermal pressure can change those parameters behind Linux back.
> 
> DVFS is currently implemented on the arm, core, h264, v3d, isp and hevc
> clocks, so updating any of them using the MMIO driver (and thus behind the
> firmware's back) can lead to troubles, the arm clock obviously being the
> most problematic.
> 
> In order to make Linux play as nice as possible with those constraints, it
> makes sense to rely on the firmware clocks as much as possible. However,
> the firmware doesn't seem to provide some equivalents to their MMIO
> counterparts, so we can't really replace that driver entirely.
> 
> Fortunately, the firmware has an interface to discover the clocks it
> exposes.
> 
> Let's use it to discover, register the clocks in the clocks framework and
> then expose them through the device tree for consumers to use them.
> 
> Cc: Michael Turquette <mturquette at baylibre.com>
> Cc: Stephen Boyd <sboyd at kernel.org>
> Cc: linux-clk at vger.kernel.org
> Acked-by: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>
> Reviewed-by: Stephen Boyd <sboyd at kernel.org>
> Tested-by: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>
> Signed-off-by: Maxime Ripard <maxime at cerno.tech>
> ---

Applied to clk-next