| Message ID | 20221018-clk-range-checks-fixes-v4-29-971d5077e7d2@cerno.tech (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | clk: Make determine_rate mandatory for muxes | expand |
On Fri, May 5, 2023 at 7:27 PM Maxime Ripard <maxime@cerno.tech> wrote: > > The Mediatek cpumux 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 consumer, the cpufreq driver, assumes the original parent to be the dedicated PLL that drives it. It gets a reference to the original parent with clk_get_parent(). It also gets an intermediate (stable) clock via DT. It does explicit clk_set_parent() calls to switch to/from the stable clock, and does clk_set_rate() on the dedicated PLL in between. So yeah, they only use set_parent hook. > 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: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> > Cc: Matthias Brugger <matthias.bgg@gmail.com> > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-mediatek@lists.infradead.org > Signed-off-by: Maxime Ripard <maxime@cerno.tech> Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
diff --git a/drivers/clk/mediatek/clk-cpumux.c b/drivers/clk/mediatek/clk-cpumux.c index da05f06192c0..a03826db4dcb 100644 --- a/drivers/clk/mediatek/clk-cpumux.c +++ b/drivers/clk/mediatek/clk-cpumux.c @@ -53,6 +53,7 @@ static int clk_cpumux_set_parent(struct clk_hw *hw, u8 index) } static const struct clk_ops clk_cpumux_ops = { + .determine_rate = clk_hw_determine_rate_no_reparent, .get_parent = clk_cpumux_get_parent, .set_parent = clk_cpumux_set_parent, };
The Mediatek cpumux 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: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Cc: Matthias Brugger <matthias.bgg@gmail.com> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-mediatek@lists.infradead.org Signed-off-by: Maxime Ripard <maxime@cerno.tech> --- drivers/clk/mediatek/clk-cpumux.c | 1 + 1 file changed, 1 insertion(+)