[PATCH v4 40/68] drm/tegra: sor: Add a determine_rate hook

[Maxime Ripard]

The Tegra sor pad clock implements a mux with a set_parent hook, but
doesn't provide a determine_rate implementation.

This is a bit odd, since set_parent() is there to, as its name implies,
change the parent of a clock. However, the most likely candidates to
trigger that parent change are either the assigned-clock-parents device
tree property or a call to clk_set_rate(), with determine_rate()
figuring out which parent is the best suited for a given rate.

The other trigger would be a call to clk_set_parent(), but it's far less
used, and it doesn't look like there's any obvious user for that clock.

Similarly, it doesn't look like the device tree using that clock driver
uses any of the assigned-clock properties on that clock.

So, the set_parent hook is effectively unused, possibly because of an
oversight. However, it could also be an explicit decision by the
original author to avoid any reparenting but through an explicit call to
clk_set_parent().

The latter case would be equivalent to setting the determine_rate
implementation to clk_hw_determine_rate_no_reparent(). Indeed, if no
determine_rate implementation is provided, clk_round_rate() (through
clk_core_round_rate_nolock()) will call itself on the parent if
CLK_SET_RATE_PARENT is set, and will not change the clock rate
otherwise.

And if it was an oversight, then we are at least explicit about our
behavior now and it can be further refined down the line.

Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: David Airlie <airlied at gmail.com>
Cc: Jonathan Hunter <jonathanh at nvidia.com>
Cc: Mikko Perttunen <mperttunen at nvidia.com>
Cc: Thierry Reding <thierry.reding at gmail.com>
Cc: dri-devel at lists.freedesktop.org
Cc: linux-tegra at vger.kernel.org
Signed-off-by: Maxime Ripard <maxime at cerno.tech>
---
 drivers/gpu/drm/tegra/sor.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/tegra/sor.c b/drivers/gpu/drm/tegra/sor.c
index fbb63d755496..abd6e3b92293 100644
--- a/drivers/gpu/drm/tegra/sor.c
+++ b/drivers/gpu/drm/tegra/sor.c
@@ -586,6 +586,7 @@ static u8 tegra_clk_sor_pad_get_parent(struct clk_hw *hw)
 }
 
 static const struct clk_ops tegra_clk_sor_pad_ops = {
+	.determine_rate = clk_hw_determine_rate_no_reparent,
 	.set_parent = tegra_clk_sor_pad_set_parent,
 	.get_parent = tegra_clk_sor_pad_get_parent,
 };

-- 
2.40.0