Re: [PATCH v2 6/8] clk: Allow parents to be specified without string names

[Jerome Brunet <jbrunet@baylibre.com>]

On Fri, 2019-03-15 at 10:16 -0700, Stephen Boyd wrote:
> Quoting Jerome Brunet (2019-03-15 03:01:53)
> > On Tue, 2019-02-26 at 14:34 -0800, Stephen Boyd wrote:
> > > ---
> > >  drivers/clk/clk.c            | 260 ++++++++++++++++++++++++++---------
> > >  include/linux/clk-provider.h |  19 +++
> > >  2 files changed, 217 insertions(+), 62 deletions(-)
> > 
> > Sorry for the delay.
> > 
> > With the fix you sent to Jeffrey
> > Tested by porting the aoclk controller of Amlogic g12a SoC.
> > This allowed to test
> >  * hws only table
> >  * parent_data with a mix of hw pointers and fw_name (with different input
> > controllers and also an input that is optional and never provided)
> > 
> > Tested-by: Jerome Brunet <jbrunet@baylibre.com>
> > 
> > With the small comment below
> > 
> > Reviewed-by Jerome Brunet <jbrunet@baylibre.com>
> > 
> 
> Awesome. Thanks! I need to Cc Rob H to hopefully get an ack on the
> concept of relying on DT so I'll resend this series again next week. It
> would also be nice if I can throw in a couple more patches to let
> drivers specify a DT node when registering a clk if they don't have a
> struct device on hand and let drivers lookup with clk_lookups somehow.
> 
> > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > index 937b8d092d17..3d01e8c56400 100644
> > > --- a/drivers/clk/clk.c
> > > +++ b/drivers/clk/clk.c
> > > @@ -39,6 +39,13 @@ static LIST_HEAD(clk_notifier_list);
> > >  
> > 
> > [...]
> > 
> > >  
> > > +static int clk_cpy_name(const char *dst, const char *src, bool must_exist)
> > > +{
> > > +     if (!src) {
> > > +             if (must_exist)
> > > +                     return -EINVAL;
> > > +             return 0;
> > > +     }
> > > +
> > > +     dst = kstrdup_const(src, GFP_KERNEL);
> > > +     if (!dst)
> > > +             return -ENOMEM;
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +static int clk_core_populate_parent_map(struct clk_core *core)
> > > +{
> > > +     const struct clk_init_data *init = core->hw->init;
> > > +     u8 num_parents = init->num_parents;
> > > +     const char * const *parent_names = init->parent_names;
> > > +     const struct clk_hw **parent_hws = init->parent_hws;
> > > +     const struct clk_parent_data *parent_data = init->parent_data;
> > > +     int i, ret = 0;
> > > +     struct clk_parent_map *parents, *parent;
> > > +
> > > +     if (!num_parents)
> > > +             return 0;
> > > +
> > > +     /*
> > > +      * Avoid unnecessary string look-ups of clk_core's possible parents by
> > > +      * having a cache of names/clk_hw pointers to clk_core pointers.
> > > +      */
> > > +     parents = kcalloc(num_parents, sizeof(*parents), GFP_KERNEL);
> > > +     core->parents = parents;
> > > +     if (!parents)
> > > +             return -ENOMEM;
> > > +
> > > +     /* Copy everything over because it might be __initdata */
> > > +     for (i = 0, parent = parents; i < num_parents; i++, parent++) {
> > > +             if (parent_names) {
> > > +                     /* throw a WARN if any entries are NULL */
> > > +                     WARN(!parent_names[i],
> > > +                             "%s: invalid NULL in %s's .parent_names\n",
> > > +                             __func__, core->name);
> > > +                     ret = clk_cpy_name(parent->name, parent_names[i],
> > > +                                        true);
> > > +             } else if (parent_data) {
> > 
> > While testing, I mistakenly left both parent_names and parent_data. I was
> > surprised that parent_data did not take precedence of parent_names.
> > 
> > Maybe it should ? (... but I understand we are not supposed to provide both)
> 
> I don't think we can. We have a problem where drivers don't initialize
> the init structure properly, opting to just throw it on the stack and
> leave junk in there that they overwrite. We'd have to go through all the
> init structures and initialize them. I suppose we could make a macro for
> that:
> 
> 	DECLARE_CLK_INIT_DATA(init);
> 
> or something like that that does this. We could bury a magic number in
> there under some debug option too so that we can make sure drivers are
> doing this properly. Otherwise we're left to doing these weird tricks
> like I've done here.
> 
> Regardless. I'll have to add a comment to this fact in the code. Thanks.
> 
> > > +                     parent->hw = parent_data[i].hw;
> > > +                     ret = clk_cpy_name(parent->fw_name,
> > > +                                        parent_data[i].fw_name, false);
> > > +                     if (!ret)
> > > +                             ret = clk_cpy_name(parent->name,
> > > +                                                parent_data[i].name,
> > > +                                                false);
> > > +             } else if (parent_hws) {
> > > +                     parent->hw = parent_hws[i];
> > > +             } else {
> > 
> > Maybe there should also some kinda of check to verify if more than one option
> > (among hws, parent_data and parent_names) was provided and throw a warn ?
> > 
> > Could be useful with drivers move away from parent_names ?
> 
> Same thing. It would be nice but we're sort of unable to do so unless we
> do what I suggest above. Should we do it?
> 

I was not thinking about anything complicated:
* Among the 3 pointers, just throw a warn if more than one is not NULL
* In the if/elseif/else, I would have put parent_data before parent_names

Nothing critical about that comment though