| Message ID | 20221018-clk-range-checks-fixes-v3-56-9a1358472d52@cerno.tech (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | clk: Make determine_rate mandatory for muxes | expand |
Hi Maxime, Le mardi 04 avril 2023 à 12:11 +0200, Maxime Ripard a écrit : > The Ingenic CGU clocks 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 candidate to > trigger that parent change is 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. > > 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(). As I said in the v2 (IIRC), clk_set_parent() is used when re-parenting from the device tree. > > The driver does implement round_rate() though, which means that we > can > change the rate of the clock, but we will never get to change the > parent. > > However, It's hard to tell whether it's been done on purpose or not. > > Since we'll start mandating a determine_rate() implementation, let's > convert the round_rate() implementation to a determine_rate(), which > will also make the current behavior explicit. And if it was an > oversight, the clock behaviour can be adjusted later on. So just to be sure, this patch won't make clk_set_rate() automatically switch parents, right? Allowing automatic re-parenting sounds like a huge can of worms... Cheers, -Paul > > Signed-off-by: Maxime Ripard <maxime@cerno.tech> > --- > drivers/clk/ingenic/cgu.c | 15 ++++++++------- > 1 file changed, 8 insertions(+), 7 deletions(-) > > diff --git a/drivers/clk/ingenic/cgu.c b/drivers/clk/ingenic/cgu.c > index 1f7ba30f5a1b..0c9c8344ad11 100644 > --- a/drivers/clk/ingenic/cgu.c > +++ b/drivers/clk/ingenic/cgu.c > @@ -491,22 +491,23 @@ ingenic_clk_calc_div(struct clk_hw *hw, > return div; > } > > -static long > -ingenic_clk_round_rate(struct clk_hw *hw, unsigned long req_rate, > - unsigned long *parent_rate) > +static int ingenic_clk_determine_rate(struct clk_hw *hw, > + struct clk_rate_request *req) > { > struct ingenic_clk *ingenic_clk = to_ingenic_clk(hw); > const struct ingenic_cgu_clk_info *clk_info = > to_clk_info(ingenic_clk); > unsigned int div = 1; > > if (clk_info->type & CGU_CLK_DIV) > - div = ingenic_clk_calc_div(hw, clk_info, > *parent_rate, req_rate); > + div = ingenic_clk_calc_div(hw, clk_info, req- > >best_parent_rate, > + req->rate); > else if (clk_info->type & CGU_CLK_FIXDIV) > div = clk_info->fixdiv.div; > else if (clk_hw_can_set_rate_parent(hw)) > - *parent_rate = req_rate; > + req->best_parent_rate = req->rate; > > - return DIV_ROUND_UP(*parent_rate, div); > + req->rate = DIV_ROUND_UP(req->best_parent_rate, div); > + return 0; > } > > static inline int ingenic_clk_check_stable(struct ingenic_cgu *cgu, > @@ -626,7 +627,7 @@ static const struct clk_ops ingenic_clk_ops = { > .set_parent = ingenic_clk_set_parent, > > .recalc_rate = ingenic_clk_recalc_rate, > - .round_rate = ingenic_clk_round_rate, > + .determine_rate = ingenic_clk_determine_rate, > .set_rate = ingenic_clk_set_rate, > > .enable = ingenic_clk_enable, >
Hi Paul, On Wed, Apr 05, 2023 at 03:04:05PM +0200, Paul Cercueil wrote: > Le mardi 04 avril 2023 à 12:11 +0200, Maxime Ripard a écrit : > > The Ingenic CGU clocks 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 candidate to > > trigger that parent change is 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. > > > > 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(). > > As I said in the v2 (IIRC), clk_set_parent() is used when re-parenting > from the device tree. Yep, it's indeed an oversight in the commit log. > > The driver does implement round_rate() though, which means that we > > can > > change the rate of the clock, but we will never get to change the > > parent. > > > > However, It's hard to tell whether it's been done on purpose or not. > > > > Since we'll start mandating a determine_rate() implementation, let's > > convert the round_rate() implementation to a determine_rate(), which > > will also make the current behavior explicit. And if it was an > > oversight, the clock behaviour can be adjusted later on. > > So just to be sure, this patch won't make clk_set_rate() automatically > switch parents, right? > > Allowing automatic re-parenting sounds like a huge can of worms... The behaviour is strictly equivalent before that patch and after: the driver will not reparent on a rate change. It just makes it explicit. Maxime
diff --git a/drivers/clk/ingenic/cgu.c b/drivers/clk/ingenic/cgu.c index 1f7ba30f5a1b..0c9c8344ad11 100644 --- a/drivers/clk/ingenic/cgu.c +++ b/drivers/clk/ingenic/cgu.c @@ -491,22 +491,23 @@ ingenic_clk_calc_div(struct clk_hw *hw, return div; } -static long -ingenic_clk_round_rate(struct clk_hw *hw, unsigned long req_rate, - unsigned long *parent_rate) +static int ingenic_clk_determine_rate(struct clk_hw *hw, + struct clk_rate_request *req) { struct ingenic_clk *ingenic_clk = to_ingenic_clk(hw); const struct ingenic_cgu_clk_info *clk_info = to_clk_info(ingenic_clk); unsigned int div = 1; if (clk_info->type & CGU_CLK_DIV) - div = ingenic_clk_calc_div(hw, clk_info, *parent_rate, req_rate); + div = ingenic_clk_calc_div(hw, clk_info, req->best_parent_rate, + req->rate); else if (clk_info->type & CGU_CLK_FIXDIV) div = clk_info->fixdiv.div; else if (clk_hw_can_set_rate_parent(hw)) - *parent_rate = req_rate; + req->best_parent_rate = req->rate; - return DIV_ROUND_UP(*parent_rate, div); + req->rate = DIV_ROUND_UP(req->best_parent_rate, div); + return 0; } static inline int ingenic_clk_check_stable(struct ingenic_cgu *cgu, @@ -626,7 +627,7 @@ static const struct clk_ops ingenic_clk_ops = { .set_parent = ingenic_clk_set_parent, .recalc_rate = ingenic_clk_recalc_rate, - .round_rate = ingenic_clk_round_rate, + .determine_rate = ingenic_clk_determine_rate, .set_rate = ingenic_clk_set_rate, .enable = ingenic_clk_enable,
The Ingenic CGU clocks 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 candidate to trigger that parent change is 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. 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 driver does implement round_rate() though, which means that we can change the rate of the clock, but we will never get to change the parent. However, It's hard to tell whether it's been done on purpose or not. Since we'll start mandating a determine_rate() implementation, let's convert the round_rate() implementation to a determine_rate(), which will also make the current behavior explicit. And if it was an oversight, the clock behaviour can be adjusted later on. Signed-off-by: Maxime Ripard <maxime@cerno.tech> --- drivers/clk/ingenic/cgu.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)