Re: [PATCH v4 61/68] clk: sprd: composite: Switch to determine_rate

[Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>]

Hi Maxime,

On 05/05/23 4:56 pm, Maxime Ripard wrote:
> The Spreadtrum composite 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.
> 
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Chunyan Zhang <zhang.lyra@gmail.com>
> Cc: Orson Zhai <orsonzhai@gmail.com>
> Acked-by: Chunyan Zhang <zhang.lyra@gmail.com>
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> ---
>   drivers/clk/sprd/composite.c | 16 +++++++++++-----
>   1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/clk/sprd/composite.c b/drivers/clk/sprd/composite.c
> index ebb644820b1e..d3a852720c07 100644
> --- a/drivers/clk/sprd/composite.c
> +++ b/drivers/clk/sprd/composite.c
> @@ -9,13 +9,19 @@
>   
>   #include "composite.h"
>   
> -static long sprd_comp_round_rate(struct clk_hw *hw, unsigned long rate,
> -				unsigned long *parent_rate)
> +static int sprd_comp_determine_rate(struct clk_hw *hw,
> +				    struct clk_rate_request *req)
>   {
>   	struct sprd_comp *cc = hw_to_sprd_comp(hw);
> +	unsigned long rate;
>   
> -	return sprd_div_helper_round_rate(&cc->common, &cc->div,
> -					 rate, parent_rate);
> +	rate = sprd_div_helper_round_rate(&cc->common, &cc->div,
> +					  req->rate, &req->best_parent_rate);
> +	if (rate < 0)
> +		return rate;

As rate is unsigned long, it can never be less than zero, so the above 
if condition is never true. Smatch detected this.

Also if we just change the type of rate from unsigned long to long, will 
the return type of the function "sprd_comp_determine_rate" being int is 
correct?

Thanks,
Harshit

> +
> +	req->rate = rate;
> +	return 0;
>   }
>   
>   static unsigned long sprd_comp_recalc_rate(struct clk_hw *hw,
> @@ -53,7 +59,7 @@ const struct clk_ops sprd_comp_ops = {
>   	.get_parent	= sprd_comp_get_parent,
>   	.set_parent	= sprd_comp_set_parent,
>   
> -	.round_rate	= sprd_comp_round_rate,
> +	.determine_rate	= sprd_comp_determine_rate,
>   	.recalc_rate	= sprd_comp_recalc_rate,
>   	.set_rate	= sprd_comp_set_rate,
>   };
>